Philosophia Scientiæ Travaux d'histoire et de philosophie des sciences

8-1 | 2004 Le problème de l’incommensurabilité, un demi- siècle après

Léna Soler (dir.)

Electronic version URL: http://journals.openedition.org/philosophiascientiae/584 DOI: 10.4000/philosophiascientiae.584 ISSN: 1775-4283

Publisher Éditions Kimé

Printed version Date of publication: 1 May 2004 ISBN: 2-84174-338-1 ISSN: 1281-2463

Electronic reference Léna Soler (dir.), Philosophia Scientiæ, 8-1 | 2004, “Le problème de l’incommensurabilité, un demi-siècle après” [Online], Online since 01 May 2004, connection on 15 January 2021. URL: http:// journals.openedition.org/philosophiascientiae/584; DOI: https://doi.org/10.4000/philosophiascientiae. 584

Tous droits réservés Introduction The Incommensurability Problem: Evolution, Current Approaches and Recent Issues

Léna Soler

The idea that competing scientific theories may be incommensurable was introduced in philosophy of science in 1962, simultaneously and independently by Thomas Kuhn and Paul Feyerabend1. Thereafter, in- commensurability promptly became one of the most central and contro- versial issues of 20th century philosophy of science. Half a century later, how has this issue evolved? The present volume of Philosophia Scientiae aims at providing the elements of an answer to this question. I will begin by stating the problem as it can be formulated today, from a point of view that allows us to distance ourselves from the most sig- nificant misunderstandings involved in the earliest discussions on incom- mensurability2 (and unfortunately still present in some recent works). This choice will allow us, at the same time, to profit by some useful distinctions that are nowadays available, but that were elaborated only at the price of careful and thorough analyses carried out over the past forty years.

1[Feyerabend 1962]; [Kuhn 1962]. On Kuhn’s conception of incommensurability and its evolution, see [Hoyningen 1989]; [Hoyningen 1990]; [Sankey 1993]; [Hoyningen 1998]. For recent books on Kuhn considering incommensurability as a particular aspect of Kuhn’s thought, see [Bird 2000]; [Laugier 2003]; [Nickless 2003]; [Read & Sharrock 2002a]. For a precise comparison of Kuhn’s and Feyerabend’s conceptions of incommensurability, conducted both at the historical and at the analytical levels, see [Hoyningen 2004]. 2For a list and an analysis of such misunderstandings, see [Hoyningen 1989, section 6.3].

Philosophia Scientiæ, 8 (1), 2004, 1–38. 2 Introduction

Yet, before beginning to state the incommensurability problem from a contemporary perspective, a brief clarification seems desirable if not required. The term ‘incommensurability’ often operates in certain areas of philosophy of science, today just as much as in the recent past, as a repulsive-term, whose rhetorical function is to stigmatize some rejected relativist-antirealist-sociological combination. As a result, a simple will- ingness to talk about the ‘incommensurability problem’ and to mani- fest interest in it is often equated with the acceptance of a relativistic- antirealist-sociological position, in a sense that remains vague but car- ries nevertheless the precise accusation of denigrating science up to an intolerable point. This may encourage to talk of the incommensurabil- ity/commensurability problem instead of the incommensurability prob- lem tout court, precisely in order to stress that there is here a philosoph- ical question — the only commitment implied being the conviction that such question potentially offers something important and interesting to think about. Now, I will not systematically use the rather unwieldy lo- cution ‘incommensurability/commensurability problem’, but it is in this spirit that I approach the problem.

The Incommensurability/Commensurability Problem

Let us now state the incommensurability/commensurability problem3. At the most general level, it is the problem of characterizing a par- ticular kind of deep transformations occurred in the history of science. The main related epistemological issues coincide with some central issues of 20th century general philosophy of science, namely, scientific realism, scientific rationality and scientific progress. It is not by chance that such problem became increasingly important in the course of the last century. Indeed, the 20th century saw the devel- opment of new scientific theories showing unexpected characteristics that seemed to break in many central respects with earlier theories. This was notably the case in physics4, that is, in the field functioning at the time as the paradigmatic object of epistemology. These deep transformations have appeared to some philosophers as a refutation of scientific realism; have led them to weaker and weaker conceptions of scientific progress

3For panoramic presentations of the problem, see [Hoyningen & Sankey 2001, vii- xxx]; [Sankey 1994a]; [Sankey 1997b]; [Soler 2000a, 180-191]. These references are most of the time useful with respect to the different particular aspects that will be examined below, although I will not systematically repeat them each time. 4Especially with quantum physics. See for example [Bitbol 1996], [D’Espagnat 2002]. The incommensurability problem 3

(so weak that their foes equate them with the claim that there is no scientific progress); and have correlatively led them to deny that there may be rational grounds for the judgement that one theory is objectively better than another. To go a little bit further, two kinds of scientific changes, and correlatively two kinds of incommensurabilities, have been pro- gressively recognized as different in principle, and are currently distin- guished in contemporary philosophy of science: the so-called ‘semantic’ and ‘methodological’ ones. 1. Let us begin with changes (and possibly incommensurability) arising at the level of theoretical contents (or at the level of content tout court 5). They are most of the time called semantical changes, and I will also label them ‘descriptive changes’6. These changes concern what rival theories ‘say’ about the object under study. They concern ontological changes in the broader sense of

5I use the expression ‘content tout court’ because I think that, at the level of contents, a generic expression in which the adjective ‘theoretical’ does not appear is needed. This in order to include, within the category of ‘contents’, propositions that the philosopher of science supposes to be assumed by scientists but that he is reluctant to label ‘theoretical’. My concern, here, is to free as much as possible the characterization of incommensurability from the ambiguities and disagreements as- sociated to the terms ‘theory’, ‘theoretical’, etc. Contemporary philosophy of science shows that the usages of the word ‘theory’ are not at all homogeneous, and that there are disagreements about what can be legitimately labeled ‘theoretical’. Such disagreements and shifts in usage can be understood as a undesirable effect of some (in themselves beneficial) insights of the last century philosophy of science. The now widely accepted thesis of the theory-ladeness of any observation, the recognition that measurement instruments are ‘materialized theories’ (according to Bachelard’s famous expression), and many other assumptions of the same kind, had together the effect that any aspect of scientific practices — experimental instrumented actions and manipulations included — can in a sense be said ‘theoretical’. But in that case, the label ‘theoretical’, being unable to discriminate anything, is useless. And if, taking the later conclusion into account, we accept that non-theoretical contents (or rela- tively less theoretical contents) are involved in scientific practices, we have to decide what we are ready to call non- or less- theoretical. Taking all that into account, I am looking for a conception of ‘contents’ sufficiently wide to cover, if required, propo- sitions not extracted from systematic high level theories. Propositions such as, for example, more or less implicit — but up to a point articulable — assumptions about the working of material devices involved in laboratory life. 6Although ‘semantic changes’ and ‘semantic incommensurability’ are the standard expressions found nowadays in the specialized literature, I prefer to talk of ‘changes in (theoretical) contents’ or ‘changes in descriptive contents’, in order to avoid possible ambiguities resulting from the fact that the semantic lexicon is used with a pecu- liar technical meaning in particular areas of our philosophy of science (for example the structural approach of science) or in fields closely linked to this philosophy (for example logic). 4 Introduction the word, that is, changes in the kinds of beings and processes supposed to populate the world according to the theory. Content changes are often analysed relying on a linguistic theory that distinguishes meaning and reference as well as intension and extension. At the level of meaning, we have the well known problem of ‘meaning change’, that comprises the question of understanding how such changes arise, how to delimitate the meaning units and legitimately conclude that they are sufficiently equivalent (synonymy) or significantly different (genuine meaning change), and with what kinds of epistemological con- sequences. And at the level of references, we find notably the question of determining whether references of key scientific terms have indeed changed in the actual history of science, as well as the question of elab- orating theories of language according to which reference is sufficiently independent of meaning to allow reference invariance despite of drastic meaning change7. 2. Side by side with changes of contents, there may be changes (and possibly incommensurability) arising at the level of the norms of research. They are most of the time called methodological changes, and I will also label them ‘axiological changes’. These are changes in the answers (often tacitly) given to questions of the kind: what is the aim of scientific research? What are the central features of a genuine investigation, of a genuine scientific theory, or of a genuine scientific explanation? What kinds of problems and solutions are authentically scientific, and what kinds are not? What are the features of a good proof, what is a convincing argument? In short, the category ‘norms of research’ comprises the whole set of values underlying scientific investigation. Changes at the level of ‘norms of research’ covers all types of axiological changes8, from the most local and apparently anecdotal ones, to the most global and visibly conse- quential ones that culminate in massive transformations of the general

7See below for more details, and notes 15 et 35 for references. 8That is why I prefer to talk of ‘norms of research’ rather than of ‘methodology’ (or ‘methodological changes’, or ‘methodological incommensurability’), despite the fact that the later expressions, and not the former, are commonly employed in the specialized literature. It is of course always possible to demand that ‘methodology’ be understood in a broad sense, so as to be able to meet all kinds of axiological changes. However, ‘methodology’ is usually understood in a narrower and stronger sense (according to which one could be reluctant to include, for example, exemplars in the Kuhnian sense). Moreover, the ‘methodology’ lexicon has quite inevitable undesirable connotations, being associated to the (now famously refuted) idea of universal algorithmic rules and procedures allowing to prove scientific hypotheses and to choose between scientific theories. The incommensurability problem 5 idea of scientificity itself. 3. The incommensurability of contents, or descriptive incom- mensurability, is more currently named ‘semantic incommensurability’ or again — in a somewhat particular interpretation of what is at is- sue — taxonomic incommensurability. It designates important differ- ences of a particular type between competing scientific theories, scientific paradigms or scientific traditions. The problem of the incommensurability of contents9 has several facets. First it consists, adopting a synchronic approach to compare two historical cross sections artificially extracted from the continuous flow of the history of science, in achieving a fine-grained characterization of the descriptive differences at stake. Roughly speaking, these differences manifest an incompatibility that is not reducible to a simple logical con- tradiction. This incompatibility is apparently related to differences in the linguistic (and more generally symbolic) resources themselves, so that intuitively, one is inclined to say that there is no common measure at the very level of what is thinkable, expressible or symbolizable. Such an incompatibility has been characterized by the late Kuhn, and is currently described in recent works, as the impossibility of translating the words of one theory (or more exactly some key words of one theory) into the vocabulary or the symbols of the other. It is in such framework that the label ‘taxonomic incommensurability’ is used10. Kuhn’s conception of taxonomic incommensurability is deeply ground- ed in a definite holistic conception of language. Roughly speaking, Kuhn’s idea — here largely re-expressed in my words — is that the set of signs used by scientists involves non-decomposable sub-systems. These sub-systems are non-decomposable, in the sense that they are clusters in which all terms reciprocally delimit their content, so that none of them can be determined without recourse to the others, nor, therefore, be taken apart without being deeply denatured. In other words, each single sig- nifier is defined by its relations to other signifiers. Put differently, each signifier takes its sense (or — depending of the chosen framework, and with nuances that will be ignored here — each takes its meaning, or con- ceptual content, or intension, or linguistic value. . . ) from the structure

9See references note 3. 10The expression ‘taxonomic incommensurability’ seems to have been introduced by H. Sankey in a paper headed, precisely, “taxonomic incommensurability” [Sankey 1998]. In addition to the references given in note 3, see [Bird 2000, chapter 5]; [Chen 1997]; [Hacking 2003]; [Kuhn 1983a]; [Kuhn 1991]; [Kuhn 1993]; [Sankey 1990]; [Sankey 1991b]; [Sankey 1992]; [Sankey 1998]; [Soler 2000b]; [Soler 2003]; [Soler 2004b]. 6 Introduction of the vocabulary (possibly including observational terms11) at the heart of which it lies. Such a fragment of taxonomy, also called by Kuhn a “lexicon”, encapsulates a network of similarity and dissimilarity relations that are applied to the world as a whole and determine what is of the same kind and what is of different kind. Kuhn talks about “local holism” [Kuhn 1983a]. In this framework, “taxonomic incommensurability” des- ignates the non-homology — or the impossibility of superimposition — of the two lexicons underlying the two theories under comparison. Kuhn insists — and this is in my opinion a very important point not always integrated by people working on incommensurability — that this non homology, which defines incommensurability and is responsible for the untranslatability, does not at all mean the impossibility of mastering the incommensurable theory. One can become bilingual, even if it requires effort and even if it is more usually the task of historians of science than the one of scientists. And once bilingual, it is possible to understand the rival incommensurable theory although it is still impossible to translate the words of one into the words of the other12. Second, the problem of semantic incommensurability also consists in the discussion, again in a synchronic perspective, about how deep the differences of contents encountered in the actual history of science are and about whether invariants can be found. Third, the problem of semantic incommensurability understood in the broader sense requires the examination, this time in a diachronic approach concerning transformations that arise along a temporal line, of the historical reasons that have led to major descriptive bifurcations. It requires the analysis of their nature and the evaluation of their cognitive value The most obvious and most debated epistemological issue pertaining to the incommensurability of scientific contents is the problem of scien- tific realism13. The simple claim that there are scientific revolutions at the descriptive level, i.e. the claim that there are, in the actual history of science, massive and deep ruptures at the level of ‘what science tells

11‘Observational’ has of course to be understood here in a contextually determined and pragmatic sense : in the sense of ‘taken to be observational for a given (indi- vidual or collective) subject at a given stage of knowledge’, that is, ‘taken to name unproblematically directly perceptible and given states of affairs’. Kuhn is ready to maintain the distinction observational/theoretical, provided that one understands the boundary as an historically-moving one (see [Kuhn 1993], and the analysis given by Emiliano Trizio in the present volume). 12[Kuhn 1983a]; [Sankey 1991c]. 13[Sankey 1994a]; [Sankey 1997c]. For recent contributions especially centred on incommensurability and realism, see for example [Brown 2001] and [Devitt 2001]. The incommensurability problem 7 us about the world’, is, in itself, already a threat for any variety of corre- spondentist or convergent realism. Yet, the more precise claim that these descriptive scientific disruptions originate from deep differences rooted in the very resources of what is expressible, is far more subversive, since it incites to question the very formulation of the problem of the rela- tion between human theories and their non-human referent. At least, it forces us to face seriously the idea of a constitutive power of language in science. And the positions adopted concerning such questions engage determined positions about scientific progress14. 4. The incommensurability of research-norms, or axiologic in- commensurability, is more currently called ‘methodological incommen- surability’. It designates important differences, tensions and incompat- ibilities between the normative idea of scientificity underlying two rival research traditions: differences between the conceptions of what is a genuine science, of what is a sound scientific explanation, of what is a scientifically acceptable proof or convincing argument, and so on. The problem of the incommensurability of research-norms15 consists, first, in the search for a fine-grained analytical characterization of such differences. Second, it consists correlatively in the discussion — conducted from a synchronic perspective contrasting two frozen pictures isolated from our history of science — about how deep are the axiological transformations encountered in the practices that we are ready to categorize as ‘science’ — considering the actual human history and the evolutions of the nor- mative idea of scientificity that this history manifests. An important aspect of such discussion corresponds to the search for invariant axio- logical features that human activities should possess to be legitimately labelled ‘scientific’. Such a quest today no longer amounts to the ques- tion about the existence of a universal and quasi-automatic scientific method enabling to find the truth, but it is, no doubt, an heir of that question reshaped in a way that allows the integration of the teachings

14On incommensurability of contents and the intertwined questions of meaning change, reference change and realism, see for example: [Achinstein 1964]; [Andersen 2001]; [Andersen 2002]; [Baltas 1990]; [Bartels 1995]; [Bird 2000]; [Carrier 2000]; [Carrier 2001]; [Carrier 2002]; [Feyerabend 1965a]; [Feyerabend 1987a]; [Field 1973]; [Kitcher 1978]; [Kitcher 1983]; [Kordig 1971]; [Kroon 1985]; [Kroon 1987]; [Kuhn 1983a]; [Kuhn 1983b]; [Kuhn 1984]; [Kuhn 1987]; [Kuhn 1989]; [Kuhn 1990]; [Kuhn 1991]; [Kuhn 1993]; [Nercessian 2001]; [Nola 1980]; [Norris 1997]; [Papineau 1979]; [Papineau 1996]; [Putnam 1973]; [Putnam 1975a]; [Putnam 1975b]; [Rasmussen 1987]; [Sankey 1991d]; [Sankey 1994a]; [Sankey 1997b]; [Shapere 1966]; [Soler 2000b]; [Soler 2003]; [Soler 2004a]; [Soler 2004b]. 15For an overview, see [Sankey 1997a]. 8 Introduction of the post-positivist philosophy of science. In any case, we cannot com- pletely avoid the question of the axiological features that are ‘essentially’ or ‘analytically’ associated with science — even if the later adjectives are most of the time understood today in a evolving and pragmatical sense referred to the scheme of family resemblances rather than to the one of necessary and sufficient conditions. Third — and maybe more important with respect to epistemologi- cal consequences that have been, in the history of philosophy of science, intimately associated with incommensurability –, the problem of axio- logical incommensurability corresponds to the task of characterizing, on a diachronic axis, the historical reasons having led to major axiological bifurcations. The central epistemological issue commonly associated with the in- commensurability of scientific norms is the problem of relativism. Rel- ativism is here understood as the problem of knowing whether human beings — and in particular human being categorized as ‘scientists’ — have at their disposal genuine justifications — or at least sufficiently good reasons — for comparing the merits of incompatible systems of cognitive norms, and especially in order to decide what is good or what is better at the level of validation procedures. The term ‘incommensura- bility’ refers here to the idea that no universal ultimate standard of that sort is available, so that there is ‘no common measure’ between different incompatible axiological options, in the sense that there is in principle no ultimate legitimate tribunal before which all different options should appear in order to be situated on a trans-historic scale of ‘cognitive sat- isfiability’. In such an epistemological configuration, widely perceived as dramatic by philosophers of science, one is quite irresistibly inclined to conclude, from the human impossibility of deciding in the absolute what is cognitively better, to the idea that all human practices and elabora- tions are on the same level and have the same value. In other words one is inclined to conclude — with despair or delectation according to one’s temperament — that relativism is inescapable. Following these lines, axiological incommensurability seems to imply relativism, and the former has often been equated with the later. Philosophy of science at the end of the 20th century showed that such a conclusion is not at all necessary — although the terminology of incom- mensurability remains widely and quasi-automatically associated with the adoption of a relativistic stance. This conclusion looks necessary only against the background of a (more or less tacit) foundationalist frame- work. Yet, several non-foundationalist strategies have been proposed in response to radically sceptical conclusions of the kind explained above: The incommensurability problem 9 forms of naturalism, revised conceptions of transcendentalism, new ex- perimentalism. . . These approaches led to non-foundationalist and non- realist – or realist in a shifted sense — accounts of scientific progress16. 5. It is worth rendering explicit that the distinction between the two kinds of incommensurability, although analytically very useful for it allows us to deal with the questions one by one, is in most real cases not a separation in re. Actual historical situations show complex inter- actions between the available scientific contents and the scientific cogni- tive values shaping the idea of scientificity in a given state of knowledge. It remains nevertheless possible, at least as a step in a philosophical re- search program labouring under the generic label of incommensurability, to isolate and explore separately circumscribed problems coming more particularly under one of the two headings of descriptive or normative incommensurability. It has moreover to be said that the methodological versus semantic incommensurability distinction is not just an analytical distinction be- tween two forms of incommensurability. It is also a distinction grounded in the social fact that there are two separate literatures on incommen- surability. The main literature that normally goes under the head of incommensurability is about semantic issues like meaning variance, ref- erence change, translation failure, etc. There is, however, an even larger literature on variation of methods, standards, norms, criteria, etc., which surrounds the topic of rational theory choice and epistemological rela- tivism and which thus concerns what have been called above ‘method- ological incommensurability’, but this literature does not currently use the term ‘incommensurability’ — although Kuhn himself started it with his talk of ‘incommensurability of standards’ in [Kuhn 1962]17. 6. Machinic-literal incommensurability. Semantical and methodological incommensurability exhaust the kinds of incommensurability commonly mentioned in most contemporary sys- tematic global presentations of the problem. However in the last decades,

16On the problem of axiological incommensurability and the intertwined questions of norm variance, rationality and relativism, see for example: Doppelt’s papers men- tioned in the bibliography; [Feyerabend 1975]; [Feyerabend 1983]; [Feyerabend 1987b]; [Forster 2000]; [Hoyningen & Sankey 2001, 159-205]; [Kitcher 1983]; [Kitcher 1993]; [Kuhn 1962]; [Lakatos & Musgrave 1970]; Laudan’s papers mentioned in the bib- liography; [Nola & Sankey 2001]; [Nola & Sankey 2000b]; [Sankey 1994b]; [Sankey 1995]; [Sankey 1996a]; [Sankey 1996b]; [Sankey 1997a]; [Shapere 1984]; [Shapere 2001]; Siegel’s papers mentioned in the bibliography; [Zheng 1988]. 17Contributors to the latter literature are people like Laudan, Doppelt, Siegel, etc., whereas contributors to the former literature are for example Putnam, Devitt, Kitcher, etc. (see references in the bibliography). 10 Introduction authors like Andrew Pickering and Ian Hacking claimed to have discov- ered “a new and fundamental type of incommensurability”18 ignored by traditional philosophers of science. Such an incommensurability concerns competing scientific practices having stabilized on the basis of different measurement processes, in- struments, machines, and laboratory practices, so that at a point they became, in Hacking’s terms, “literally” incommensurable, in the sense that there is, properly speaking, no shared physical measure between them. Pickering calls the same kind of configuration “machinic incom- mensurability” [Pickering 1995, 189]. The relation between the 1960s and the 1970s particle physics offers for example, according to Pickering, a striking example of machinic incommensurability19. The idea of literal or machinic incommensurability has been rela- tively recently introduced and has not been widely discussed — at least with reference to the traditional incommensurability problem and if we compare with the immense literature devoted to traditional forms of in- commensurability. Pickering and Hacking presented it as new and intro- duced it in contrast with language-based characterizations and theory- dominated orientations — claiming for example that it “has nothing to do with ‘meaning change’ and other semantic notions that have been associated with incommensurability” [Hacking 1992, 56-57]. However, the novelty of what is at stake and, more important, its ex- act relations with the traditional forms of incommensurability, deserve in my opinion more discussion20. As far as I can understand the situa- tion on the basis of the fragmentary investigations already undertaken, my provisional conclusion is the following. ‘Machinic-literal incommen- surability’ is not a new kind of incommensurability, in the sense that

18[Hacking 1992, 54]. Also quoted by [Pickering 1995, 187]. 19For the detailed study of the historical case, see [Pickering 1984]. The relations between such historical case itself and incommensurability is first characterized in [Pickering 1984, section 14.3]. For later developments and re-qualification in the framework of Pickering’s conception of the “Mangle of practice”, see [Pickering 1995]. It is only in that last book that the expression “machinic incommensurability” ap- pears. For studies not all especially centered on incommensurability but that provide elements connected with the idea of a ‘pragmatic incommensurability’ arising at the level of experimental practices, see also [Ackermann 1985], [Bensaude-Vincent 1993], [Bensaude-Vincent & Stenger 2001], [Buchwald 1995], [Collier 1984], [Galison 1987], [Gooding 1992], [Hacking 1983], [Hacking 1988], [Hacking 1999], [Latour 1997], [Pick- ering 1994]. 20I recently examined the question in three talks: a first one given in Montreal in September 2003 at a conference organized by the SOPHA (now submitted for publication); and in two later talks given in October and March 2004, in the context of my seminar devoted to the incommensurability problem at the Collège International de Philosophie, Paris. The incommensurability problem 11 what it refers to does not require the introduction of a third additional category side by side with those of incommensurability of contents and incommensurability of norms. However, the study of what is at stake may introduce some novelty in the classical characterization of the in- commensurability problem, since ‘machinic-literal incommensurability’ involves a shift in the grammatical subject of incommensurability. In- deed, what is classically termed ‘incommensurable’ is ‘something’ at the level of theoretical practices, whereas here, it is ‘something’ at the level of experimental practices (the problem being then: what exactly? With what epistemological consequences? And: do such consequences legit- imize the recourse to the incommensurable lexicon?). 7. Understood according to the presentation given above, the in- commensurability problem covers a broad and complex network of ques- tions. Thus choices had to be made concerning the composition of the present volume. The volume takes incommensurability of con- tents as the starting point, and it is led from there to touch on other dimensions or species of incommensurability. Two papers are especially devoted to machinic-literal incommensurability. However, axiological in- commensurability is not directly tackled and remains more or less in the background21. Such a choice follows, in a way, the historical movement of the in- commensurability debate — hoping that this will serve the aim of under- standing better the present state of the problem. Indeed the incommen- surability problem, after its introduction and the early attempts of clar- ifications in the sixties, progressively shrank, in the actual discussions of philosophers of science, to the more restricted problem of semantic incommensurability. This arose notably under the influence of Kuhn’s later stress on language, taxonomic structures and translation, as a sort of retarded incidence of the so-called ‘linguistic turn’. Philosophers of science did not, in this movement, completely abandon the constellation of questions listed above under the heading of ‘axiological incommensu- rability’. But they did not establish a systematic and explicit association between these questions and the incommensurability label22. Now in re- cent decades, the previously circumscribed incommensurability problem has been re-enlarged afresh, with attempts to include in the picture the instrumental, experimental layer of scientific activities, this time in the broader context of the so-called ‘pragmatic turn’.

21For a recent book on incommensurability making room to methodological in- commensurability side by side with semantic incommensurability, see [Hoyningen & Sankey 2001]. 22See [Sankey 1994a]. 12 Introduction

Current Approaches to Incommensurability

Before presenting one by one the different papers constituting the present book, let us have a brief overview of the main methodological options nowadays available and alive in studies on incommensurability. Without claiming that the contributions of the book offer an exhaustive sample of the existing options, I have been anxious to make room to different and often opposed ones. Not surprisingly, the main trends constituting contemporary reflec- tions on science are also found in special studies focused on the incom- mensurability problem. We will consider here, first the analytical ver- sus historical ways of examining science, then the linguistic, pragmatic and cognitive approaches of incommensurability, and finally, more spe- cific and sometimes overlapping orientations such as the Wittgenstein- inspired one. 1. The distinction between the analytical and the historical approaches of science has often been thought, especially in the anglo- saxon world before the sixties, as an opposition and a quite strong one. Even today, it is still conceived as an opposition in certain areas of phi- losophy of science. However, this general tendency became less and less important within the group of philosophers studying incommensurabil- ity. Within this group the analytical and the historical determinations widely appear today to be two complementary and required approaches rather than two mutually exclusive ones. Almost all authors working on incommensurability today are anxious to examine available historical case studies (if not to explore themselves particular historical scientific episodes), in order to achieve a characterization of incommensurability both inspired by and conformed to historical ‘data’ about scientific de- velopment. One of the ‘fathers of incommensurability’, namely Kuhn, himself contributed very much, as it is well-known, to the progressive recognition, in the anglo-saxon world, of the necessity of taking the his- torical dimension into account when tackling many central questions of philosophy of science and notably the incommensurability problem23. 2. The linguistic approach has been adopted by Feyerabend in his early characterization of incommensurability24, as well as by the late Kuhn25, and it is through it that incommensurability has been most widely and deeply explored. In the present volume, this approach is typically represented by the works of Alexander Bird, Martin Carrier

23See especially [Kuhn 1962] and [Kuhn 1992]. 24See reference note 1. 25See references note 10. The incommensurability problem 13 and Léna Soler. The papers of Hanne Andersen, Soazig Le Bihan and Emiliano Trizio, although they are less prototypical of works committed to the linguistic approach and although they explicitly aim at considering non-linguistic aspects of incommensurability, are also closely linked to the linguistic dimension in several important respects. The linguistic approach to science is often accused of reducing science to language or of being too restricted to achieve a sound characterization of science. However, it is in my opinion neither fair to much work focused on the linguistic dimension, nor philosophically fruitful, to equate it with the positive strong thesis that science is essentially a linguistic reality and nothing more. The emphasis on the linguistic dimension may more productively be understood as a methodological orientation aiming at characterizing an important but not exhaustive dimension of the studied object. This being said, to choose to characterize incommensurability by a linguistic approach is of course not a neutral choice. Assuming that it is coherent, such a choice presupposes the minimal belief that incommensurability of scientific contents corresponds to drastic linguistic changes. The task is then to analyse such changes with the help of a suitable theory of language: to find or elaborate a linguistic framework able to account for the phenomena associated with incommensurability. We can classify the possible theories by means of schematic traditional oppo- sitions, such as atomistic versus holistic conceptions; extensive versus intensive characterizations; non-descriptive models centred on reference (the most famous being the so-called ‘causal theory of reference’) versus models focused on sense and descriptive aspects; theories relying on the idea of necessary and sufficient conditions governing the ascriptions of meaning and reference, versus theories relying on the weaker, Wittgen- steinian idea of family resemblances. . . The question concerning the most suitable linguistic framework is still a much debated issue today. However, dominant trends emerged in the course of the 20th century that influenced the discussion of the incommensurability problem. First, it has been largely recognized that the paradigm of necessary and sufficient conditions did not govern actual scientific linguistic usage. Such a recognition led philosophers to cope with indeterminacies linked to the working of language — the most famous one being the Quinian indeterminacy of translation — and to analyse the way these indetermi- nacies affect judgments of incommensurability26. Correlatively, it gave

26See [Field 1973]; [Norris 1997]; [Quine 1960], [Quine 1969] and [Quine 1987]; 14 Introduction rise to developmental perspectives focused on linguistic learning pro- cesses, often in close connexion to empirical studies coming from cultural anthropology or, more recently, cognitive sciences. Second, it has been widely admitted that holistic aspects of scientific languages had to be taken seriously and to be integrated in the charac- terization of incommensurability. Consequently the discussion has been directed to the strength of such holism and on the associated problem of extracting and delimitating significant linguistic units (units that can be legitimately considered to have a sufficient autonomy relatively to the larger linguistic system to which they pertain). This gave rise to the problem of local/global incommensurability27. It has been realised, thirdly, that reference-determination of sci- entific terms was never absolutely independent of meaning- or sense- determinations, and this led to the elaboration of mixed theories of reference combining descriptive and non-descriptive (often conceived as causal) factors. Many people wishing to show that incommensurabil- ity is not a threat for realism since it can be conciliated with trans- paradigmatic continuity of the reference of scientific terms, have built on such mixed accounts28. Fourth, as it is well known, the impossibility of drawing an absolute- invariant-natural frontier between the observational and the theoreti- cal levels has appeared ineluctable. We are thus left with the problem of reconciliating the need of the distinction with the inescapability of its relativization. This problem is of course intimately associated with holism and with the dependence of reference on sense: the observa- tional/theoretical demarcation is a moving one since intuitively obser- vational terms are not independent of other terms, including intuitively theoretical terms. These intertwined recognitions and their associated difficulties lead to what has often appeared as an important paradox. Incommensurable theories have to be competing theories, otherwise the judgment of incom- mensurability is epistemologically trivial and deprived of any interesting consequence (think, for example, of the claim that thermodynamics and the theory of the unconscious are incommensurable). Yet by definition, competing theories target a common realm of phenomena, which means that they must admit shared observations (observations for which they

[Sankey 1991a]; [Soler 2004a]; [Weed 1997]. 27Kuhn introduced local holism and incommensurability in [Kuhn 1983a]; see [Hoyningen 1989, 112ff]. See also [Carrier 2001], [Chen 1990], [Soler 2000b] and [Soler 2003]. 28For more details and references, see note 35. The incommensurability problem 15 both claim responsibility). Thus we must be able to extract a com- mon observational layer assumed by both of them. This amounts to saying that we must retain something of the observational/theoretical dichotomy and make its sense clear. And this amounts at the same time to the assumption of local holism and to tackling the difficulty of stating how to recognize sufficiently independent clusters of terms and statement in concrete cases, how to separate incommensurable concepts from commensurable ones. But if all of this is admitted, it seems now that the so-called incommensurable theories are not so incommensurable after all, since they have a phenomenal common measure29. Aspects of this paradox are examined in some works of the present volume. People working within the linguistic approach may have very differ- ent philosophical aims and outlooks. The latter are most of the time already apparent in the linguistic options that each author favours. As an illustration, we can compare Bird’s and Carrier’s work on incommen- surability. Bird ultimately aims at defending scientific realism and at showing that incommensurability is harmless for scientific realism. In order to do so he favours, like many realist-oriented thinkers, to rely on an accommodated causal theory of reference. Carrier, for his part, assumes that there indeed are drastic descriptive revolutions involving drastic changes in reference, so that common versions of scientific realism are indeed threatened; and he assumes correlatively that causal theories of reference are of little use to save realism (which does not mean, Carrier insists, that we are committed to strong relativism, since rival incom- mensurable theories, although untranslatable, can be compared with re- spect to their empirical adequacy). This being admitted, Carrier favours a Wittgenstein-inspired (contextual and pragmatic) theory of meaning, and intends to provide in such framework a refined characterization of Kuhn’s taxonomic incommensurability. 3. Approaching incommensurability with a pragmatic perspective constitutes another option, more and more praised, along the 20th cen- tury, in studies of incommensurability as well in other areas of studies re- flecting on sciences. Although part of Kuhn’s originality in [Kuhn 1962] was to emphasize pragmatic and implicit factors inherent to scientific activity, Kuhn’s later language-based characterization of incommensu- rability took little notice of this dimension, to the regret of some of his readers. In this volume, the pragmatic approach to incommensurability is represented by the papers of Michel Bitbol and Emiliano Trizio. Pragmatic oriented studies interested in the incommensurability prob- 29Around these lines of thought, see [Carrier 2001], [Feyerabend 1972]; [Shapere 1964]; [Soler 2003]; [Soler 2004a]. 16 Introduction lem have most of the time grown in opposition to language- and high- level-theory-centred accounts. Science, they urged, cannot be reduced to language and is an activity involving many other essential dimensions. No more can science be reduced to the production of high-level theories aiming at describing the world: science is as much — and in some ac- counts primarily — an empirical and most of the time experimental con- crete activity involving concrete material objects and concrete actions- manipulations (for example the ones constituting laboratory life). Thus, a complete characterization of incommensurability cannot itself be re- duced to linguistic characterizations and theory comparison. It must include non-linguistic, non-theoretical concrete aspects of scientific prac- tices. And it must take into account the non-explicit and in principle not totally verbalizable elements that irreducibly constitute scientific activities. This is maintained, not only with respect to the level of the- orization (for example more or less local know-how concerning abstract problems resolution, partially tacit goals and values constraining theo- retical options, etc.), but also with respect to the level of laboratory life (for example more or less local know-how concerning the manipulation of instruments and the interpretation of machinic termini, partially tacit goals and values constraining experimental options, etc.). On the basis of these shared requirements, the problem is how to elaborate an adequate framework allowing us to describe scientific prac- tices in all their richness and variety. It is at this level that some dis- agreements arise. Some concern the elaboration and the choice of the relevant variables30. Others concern the allowed and best ways to access to the tacit aspects of science and render them graspable. Still others concern the relations that can hold in principle, or that actually hold in concrete historical cases, between high-level theoretical practices and experimental laboratory practices. What is the most suitable model? A model in which one of the two poles is understood (possibly alternately) as the driving force conditioning the evolution of the other, if not as the cause determining such evolution? Or an interactionist model in which each actual scientific stage of development is understood as the emergent symbiotic result of a complex holistic equilibrium in which all elements mutually support each other? Do the two poles have a certain relative autonomy, and if it is the case, to what extent? And so on31. It is in such a framework that the incommensurability labelled “lit- eral” by Hacking and “machinic” by Pickering takes place. As for the present volume, Michel Bitbol examines the idea of an incommensura-

30See for example [Hacking 1992, sections 6-9] 31For references, see note 19. The incommensurability problem 17 bility of laboratory life, on the one hand with reference to the Kuhnian and traditional linguistic-based characterizations of incommensurability, and on the other hand in the light of Pickering’s and Hacking’s account of science and literal incommensurability. Emiliano Trizio, for his part, explores the relations between literal incommensurability and taxonomic incommensurability, arguing that the alleged gap between them can be filled. 4. It would be and exaggeration to talk about a cognitive approach to incommensurability, since incommensurability is not a special focus of the proliferating field of cognitive studies. There are, nevertheless, analyses of the incommensurability problem that intend to rely on the results of some cognitive studies, or that want to confront such results with the hypotheses involved in a particular characterization of incom- mensurability32. The paper of Andersen included in the present book is linked with this trend. As it is well known, the so called cognitive sciences intend to achieve a characterization of cognition grounded in empirical results and informed by studies produced by a cluster of different disciplines. As language is an aspect of cognition, connections have been established between cog- nitive sciences and the linguistic approach to incommensurability. This holds especially for the taxonomic characterization of incommensurabil- ity. The taxonomic characterization historically developed in close asso- ciation with considerations about language acquisition and conceptual learning processes (Kuhn himself has been committed to this trend and strongly contributed to reinforcing it, if not to inaugurating it). Cog- nitive sciences have something to say about such processes. This part of cognitive studies is certainly the most exploited one in cognitively- informed philosophical reflections on the incommensurability problem — usually for the purpose of finding empirical support in favour of philo- sophical theses. This is the line followed by Hanne Andersen in the present volume, cognitive sciences being convened in order to sustain a conception of incommensurability based on dynamical frames. 5. What can be called the Wittgensteinian approach to sci- ence and incommensurability33 has a certain autonomy with respect to the linguistic and pragmatic approaches even if it is intertwined with them in several respects. The paper of Aristides Baltas contained in the

32[Andersen, Barker & Chen 1996]; [Barker 2001]; [Barker, Chen & Andersen 2003]; [Bird 2002b]; [Bird 2004]; [Chen, Andersen & Barker 1998]; [Nercessian & Andersen 1997]. 33See for example the works of A. Baltas, M. Bitbol, M. Carrier, V. Kindi and R. Read mentioned in the bibliography. See also [Andersen 2000]. 18 Introduction present volume represents this tendency. The one of Martin Carrier is also linked to it, although less directly, since it is developed on the basis of a Wittgensteinian-inspired theory of language. Wittgenstein-inspired accounts of incommensurability have become more and more praised in recent decades and constitute a living active tendency today. They are often part of a broader project aiming at reading Kuhn from a Wittgensteinian perspective. Kuhn, as he explic- itly recognized, has been influenced by the philosophy of Wittgenstein, especially by Wittgenstein’s conception of language. Many followers of Wittgenstein appreciate Kuhn’s work because of its intimate proximity to their orientation. One has even been up to call Kuhn “a Wittgen- steinian of the sciences”34. Approaching incommensurability in a Wittgensteinian framework con- sists most of the time in the adoption of some Wittgenstenian key- concepts and fundamental insights for the purpose of clarifying what is really at stake. Language-games, forms of life, grammar, ‘meaning is use’, family resemblances, etc., are put at the service of the task of clarifying incommensurability and renewing its characterization. Such attempts integrate most of the time some pragmatic aspects of incom- mensurability, without ignoring its linguistic dimension (the later being — depending of the authors — more or less important in the whole pic- ture), so that many connexions and reciprocal teachings can be found between the Wittgensteinian approach on the one hand, and the neo- pragmatic and linguistic ones on the other. In his article, Aristides Baltas intends to understand incommensurability as a change of gram- matical space. In order to do so he takes into account linguistic changes involving non-explicit aspects of language, without reducing incommen- surability to a purely linguistic phenomenon.

Survey of the Contributions

1. Alexander Bird gives a contribution to a debate that began in the Seventies and is still alive nowadays through ever more refined argu- ments. At the most general level, the question is to know up to what point incommensurability threatens trans-paradigmatic stability of the refer- ence of scientific terms. The central epistemological issue at stake is scientific realism. Indeed, it is difficult to support realism without a min- imum of historical continuity. Yet, the thesis that the history of science

34[Read 2003]. The incommensurability problem 19 shows the existence of scientific revolutions with corresponding pre- and post-revolutionary incommensurable theories, is precisely the negation of cumulative scientific development. The strategy of many realists have been to try to save cumulativity by preserving a certain continuity at the level of reference. They have intended to show that, although there indeed are scientific revolutions at the level of concepts and meanings, the reference of most scientific terms is nevertheless preserved. To achieve that goal, most realists tried, at the beginning at least, to rely on the so-called ‘causal theory of reference’ (CTR). As it is well known, the CTR has first been elaborated by Kripke for proper names [Kripke, 1980], and has later been tentatively applied to kind terms. Roughly speaking, the idea is that human dubbing is rigidly linked to — since it is caused by — bits of reality through inaugural acts of baptism, so that the name continues to refer through time, despite any possible later changes of human beliefs, to the original reference — the real sub- stance, thing, property. . . — actually involved in the original baptism. Many authors tried to use the idea, or variants of it, against unde- sirable epistemological consequences of incommensurability. Hilary Put- nam’s attempt is certainly the most famous one [Putnam 1973], [Putnam 1975a], [Putnam 1975b]. It initiated a quite famous dialogue with Kuhn ([Kuhn 1989], [Kuhn 1990]) and developed well-known exemplars such as the one of twin-earth and twin-H2O. But since then, there have been many other less known interesting attempts to apply the CTR to theory change as well as to modify the CTR. Attempts to modify it have often developed in response to the criticism that a pure CTR deprived of any descriptive elements is untenable (or is useless because it is impossible to apply it to concrete historical cases). Refined versions of CTR, espe- cially mixed versions including a minimum of descriptive elements side by side with the causal non-descriptive ones, have then been elaborated, providing the basis of a rich and sometimes technical literature on the relations between incommensurability, realism and the CTR35. In his book published in 2000, T. Kuhn, Alexander Bird defends the thesis that, in most historical scientific transitions commonly considered as revolutionary, reference continuity is indeed preserved. Discussing the situation of incommensurable theories in the framework of the CTR, he

35See for example [Bird 2000, chapter 5]; [Devitt & Sterelny 1987]; [Kitcher 1978]; [Kitcher 1983]; [Kordig 1971]; [Kroon 1985]; [Kroon 1987]; [Kroon & Nola 2001]; [Nola 1980]; [Norris 1997]; [Papineau 1979]; [Papineau 1996]; [Putnam 1973]; [Putnam 1975a]; [Putnam 1975b]; [Sankey 1991d]; [Sankey 1994a]; [Sankey 1997b]. For critical reactions to realist attempts based on CTR, see for example [Feyerabend 1987a], [Kuhn 1989], [Kuhn 1990] and [Read & Sharrok 2002b]. 20 Introduction admits Kuhn’s last definition of incommensurability as untranslatability, but argues that untranslatability names transformations circumscribed to the level of sense, so that the reference remains untouched. In so doing he studies Kuhn’s reply to Putnam, reconsidering Kuhn’s arguments about cases such as ‘gold’ and ‘water’. In response to Bird’s book, Rupert Read and Wes Sharrock promptly criticized Bird’s arguments in a paper published in 2002 [Read & Sharrok 2002b]. The paper of Bird published in the present volume is a reply to these criticisms. Bird understands these criticism as claiming the incompatibility, not only in fact but also in principle, of the referentialist versions of scientific realism on the one hand, and incommensurability as conceived by the last Kuhn on the other hand. This is the central general claim he wants to refute, but he also turns to several more specific ones. Having sketched the general content and central issues of the debate, Bird began to distinguish two “entirely distinct” but often conflated posi- tions: on the one hand referentialism, defined as “the idea that reference is a key concept in assessing the progress of science and that there has been a large measure of referential continuity over time, even over rev- olutions”; and on the other hand essentialism, defined as “the view that natural kinds and perhaps also natural properties have essential charac- teristics”. He regards as inaccurates Read and Sharrock’s characteriza- tion of referentialism as “a kind of essentialism” — although he recognizes intimate relations between essentialism and putnamian referentialism. Bird examines two versions of referentialism. The first one, called the “Fregean version” (although it is certainly not literally fregean), holds that sense determines reference. Bird argues that it is not a good re- sponse to incommensurabilism, firstly because too much of the theory may contribute to the reference determination, so that theory change may well imply reference change, and secondly because it moreover presents internal troubles, arising from the impossibility to draw a sharp dividing line between propositions contributing to sense and proposi- tions contributing to reference. The second version of referentialism, called the “Kripke-Putnam version” and described as a “causal (...) ex- ternalist conception of reference determination”, has Bird’s favor, at least as far as kind terms are concerned. True, “the causal theory of reference does not in itself guarantee continuity of reference”. But according to Bird, it “shows how there can be continuity of reference despite even revolutionary scientific changes, and shows how scientific realism is not threatened by the thesis of incommensurability as Kuhn formulated it”. In such a framework, Bird scrutinizes one by one the objections of Kuhn, Read and Sharrock against the Kipke-Putnam version of the The incommensurability problem 21

CTR, relying mainly on the example of the H2O case. The first ob- jection, raised by Kuhn, concerns the impossibility – in the sense of an incompatibility with modern chemistry — of an XYZ substance having all the superficially observable properties of our H2O. Against it, Bird first insists that Putnam’s scenario has only to be imaginable, and not realizable in our world. The next objection examined reflects on a variation of Putnam’s ini- tial scenario involving Twin-Earth. Such an alternative scenario had been introduced by Bird in his book on Kuhn. Bird suggests we recon- sider Putnam’s argument, situating it in the early nineteenth century, that is, at a time where scientists did already know that water is H2O but were not sure that there is no distinct compound sharing the su- perficial properties of water. In such a situation, Bird claims, “it is not open to a putative forerunner of Kuhn’s to object that there could be no such XYZ that has the superficial properties of water but is a different compound”. Read and Sharrock protest that in such situation, “there no longer is a thought-experiment”, since the impossibility mentionned by Kuhn is an impossibility that refers to a given scientific state and taxonomic structure characterized by a strong solidarity between the assumption that water is H2O and the assumption that XYZ does not exist. Bird dissects this interpretation of this answer in three assertions that he successively intends to refute, accusing Read and Sharrock at the same time of misunderstanding Putnam’s argument, assuming what Putnam’s argument wants to disprove, and standing in opposition to the commitments of chemists. From this and other considerations, Bird comes to the strong con- clusion that water “functions like a name and so is a rigid designator” picking out natural kinds, and that in consequence, “ ‘water is H2O’ is a necessary truth” — now making the connection between (putnamian) referentialism and essentialism. He reflects then on the delicate clause ‘to be a sample of a particular kind’ or ‘to be a sample of the same kind’, ad- mitting at the same time that “members of the same kind must bear some deeper similarity than mere superficial resemblances” and that “’same- ness in kind’ may be fixed contextually” by chemist’s interests. This leads him to consider another objection of Read and Sharrock, address- ing the fact that much of what is ordinary called water is not exclusively H2O (due to impurities). For this reason, referentialists like Bird com- monly appeal to modalities in their quasi-essentialist statements, saying, for example, that “’in al possible worlds water consists (largely) ofH2O” (my emphasizes). But then there arises the question, posed by Read and Sharrock and recurrently addressed to the CTR, of whether “essentialism 22 Introduction would look so attractive if the impurities included XYZ, in significant proportions (say 25%)”. Bird answers, first in appealing to the contextuality of the sameness in kind relation. According to the context, we have to distinguish different extensions of the term ‘water’. Now, the extension of ‘water’ as used in the context of chemistry is not the same than the extension of our everyday term ‘water’. The first one covers exclusively H2O, whereas the second one includes impure samples. Bird admits in consequence that the adjective ‘largely’ should be dropped in the essentialist assertion above, as long as we are dealing with the chemical term ‘water’. He focuses then, second, on the empirically not forbidden case in which all our samples of water would be discovered by chemists to contain a large proportion of XYZ. In such case, Bird concludes, “we would have to admit that pure water is not a single chemical kind but is a mixture of two compounds. And it would certainly be plausible to argue that water has no real essence (although some might reasonably argue that it is essentially a mixture of H2O and XYZ)”. But such a possibility, he continues, “does not show that in the actual case, where our samples are not such a mixture, water is not essentially H2O”. Hence, Bird is finally committed to what I would call a ‘revisable es- sentialism’, according to which essence ascriptions are in principle always destabilizable by in principle always possible future scientific revolution- ary discoveries of the kind just mentioned above. The necessity of “all water consists in H2O” is therefore a conditional necessity, hanging on the assumption that our science will not meet such destabilizations, the latter assumption being in turn fed by the realist credo that our science has indeed grasped enough of the actual elements composing the world. Bird also examines Kuhn’s developments about the evolutions of our beliefs concerning the three states of water. Kuhn emphasizes the taxo- nomic transformation having accompanied the transition from the belief that liquidity is an essential property of water, to the belief that some- thing else is and that ice and steam as genuine water. Bird argues, first that Kuhn’s point is historically inaccurate (many people including Aris- totle equated ice and steam with water). Second, that even if it were true that some chemists considered steam and ice as different species, it is not enough to prove that the extension of the term ‘water’ does not cover steam and ice. And third, that even if ‘water’ analytically entailed ‘liquid’ in 1750, it would not be damaging for the essentialist, who could continue to hold that water1750 essentially contains H2O. Finally, Bird makes some brief remarks on the relation between super- ficial and ‘deep’ properties with respect to the question their necessity. The incommensurability problem 23

This is a response to a development of Kuhn, in which Kuhn points out the fundamental solidarity between the elements of the lexical scien- tific structure, from which he emphasizes that “the so called superficial properties are no less necessary than their apparent essential successors”. Bird remains very allusive here, but he accuses Kuhn of irrelevancy and call for more refined analytical distinctions and studies. He insists on the need to scrutinize the multiplicity of the plausible configurations (neces- sary superficial properties and necessary laws of nature; contingent laws of nature and contingent superficial properties; contingent laws of nature and necessary superficial properties. . . ). And he points that necessary properties are not in every case essential properties. On the whole Bird concludes that Kuhn’s arguments, despite of the efforts of Read an Sharrock to resurrect and develop them, in themselves “do not give the scientific realist a reason to doubt her view”. According to him, the referentialist defense of scientific realism is not threatened by incommensurability equated with untranslatability. 2. Highly different are the approach and the conclusions of Martin Carrier — and this illustrates that very divergent positions continue to constitute the debate on incommensurability nowadays. Let us quote Martin Carrier’s last sentence: “The lesson incommensurability teaches is that in the course of theory change, scientific achievements may be conceptually reframed beyond recognition. In particular, the occurrence of reference shifts poses a serious threat to the claim that scientific the- ories accomplish an ever deeper understanding of the same objects and processes. In this respect the incommensurability thesis retains some epistemic significance after all”. Correlatively, Carrier’s confidence in the usefulness of the CTR in relation to these questions appears very limited36. In his paper, Martin Carrier reconsiders semantic incommensurabil- ity, equated with unstranlatability, in the framework of the “theoretical context account” or “context theory” of meaning, as Kuhn and Feyer- abend did themselves. He intends to show in the same movement, first that semantic incommensurability is indeed instantiated in history of science, and second, that a coherent reconstruction of the notion can be proposed on the basis of an holistic-contextual theory of meaning. Such a reconstruction of semantic incommensurability is here de- veloped and illustrated relying on an historical case largely considered

36In the present volume M. Carrier remains silent about the CTR. But in other papers he appears at least reluctant to it. See [Carrier 2001, 81] and [Carrier 2002, 141, footnote 2]. 24 Introduction as revolutionary among historians and philosophers of science, namely, Lorentzian electrodynamics versus Einsteinian special relativity. Through this example Martin Carrier intends to show why it turns to be impos- sible to translate one into another central concepts of both theories (in the example the concept of velocity and the concept of mass). The skeleton of the argument is the following. According to the theoretical context account, meaning has two main determinants: the inferential integration (i.e. the relations of a given concept to other concepts); and the conditions of application (associated with the set of situations to which a given concept is thought to apply and not to apply). A good translation has to preserve meaning. It has thus to satisfy two demands: preservation of the inferential relations, and retention of the conditions of application. Incommensurable concept are untranslatable, because in their case, only one of these two demands can be fulfilled, but never both of them. The ultimate reason of such an impossibility lies, according to Mar- tin Carrier, in the fact that the two rival theories assume contrasting and incompatible set of laws, that is, deep divergences at the level of the corresponding inferential relations. As a consequence of this nomological change, natural kinds are restructured: very different and often incom- patible classes of equivalence hold before and after a revolution (what was thought to be different may be thought of the same type; radically new ‘natural’ kinds may appear; old central ‘natural’ kinds may com- pletely disappear. . . ). With respect to this point, Martin Carrier claims to reverse the order of priority assumed by Kuhn between nomological change and split up of scientific kinds. True, the last Kuhn put the re- structuring of kind taxonomy at the center, and seemed thus to assume kind restructurings to be the primary factor and nomological change to be a derived secondary feature. Martin Carrier last aim is to show that semantic incommensurability, understood in the way previously spelled out, is not at all the threat it has often appeared to be for rational theory comparison. According to him, “empirical comparison does not require translation and remains largely unaffected by incommensurability”. He illustrates the point on two examples: the series of experiments performed by Walter Kaufmann between 1901 and 1905, intended to measure the dependence of the mass of electrons upon their velocity; and the Kennedy-Thorndike experiment of 1932 aiming at comparing Lorentz’s and Einstein’s theories in the spirit of Michelson-Morley experiments. In order to argue the point, Martin Carrier begins to emphasize that incommensurable theories, not only de facto have, considering proto- The incommensurability problem 25 typical historical cases, shared relevant phenomena, but moreover must have such shared phenomena. Otherwise, incommensurability would be epistemologically non significant. “A conflict between two theories only emerges if there is some shared realm which they jointly address”; “Ad- vocates of each theories have to acknowledge responsibility for coping with these phenomena (which may be disparately understood in either theory). But this much of a common ground is secured by the mere fact that we are dealing with incommensurable theories”. We encounter here the delicate question, already introduced above in the general presentation, of the ineluctable tension existing between incommensurability understood as a complete absence of common mea- sure, and the requirement that incommensurable theories must be com- peting theories (if incommensurability is to name an interesting prob- lem) and must therefore have some common phenomenal measure. And we see how Martin Carrier overcomes such difficulty: by assuming a sort of analytical link between incommensurability and the requirement to claim responsibility for at least some identical targeted phenomena. Each camp will describe and interpret these common experiments and re- sults differently, within his own conceptual incommensurable framework, and each will evaluate the significance of the corresponding interpreted results for his own theory. With respect to these task, “no need for trans- lation arises”. Thus incommensurability understood as untranslatability, although real, does not prevent empirical comparison. Moreover, such an empirical comparison can be performed by one and the same person, because of the possibility, elaborated by Kuhn, of bilingualism. From all this Martin Carrier concludes that incommensurability, un- derstood as untranslatability in the sense specified in the paper, is ground- ed in “incompatibility rather than unrelatedness”. In fact, incommensu- rability results from a tension between deep differences and required similarities. On the one hand, incommensurable concepts do not satisfy both the demands of sameness of conditions of application and preser- vation of theoretical integration. But on the other hand, “the converse aspects deserves emphasis as well: incommensurable concepts exhibit a particular type of relationship to each other; they are connected with one another by empirical or theoretical ties”. And the difference mani- fested through translation failure is not any kind of difference, so that the translation failure characteristic of incommensurability is itself not any kind of translation failure. “Not any old taxonomic disagreement is sufficient for producing incommensurability”. “It is a distinctive fea- ture of incommensurability that the relevant classificatory discrepancies resist reciprocal adaptation because they arise from fundamental theo- 26 Introduction retical divergence. Non-translatability due to incommensurability is not the result of a simple conceptual gap. Incommensurability is not about an accidentally missing word; it is rather about an in-principle rift”. As we shall see, such conclusions are very close to the one endorsed by Hanne Andersen in this book. 3. Martin Carrier’s paper is the object of three commentaries, which are the written (sometimes enlarged) versions of talks given in march 2002 in Nancy, at the occasion of a day organized by the Poincaré Archives in honor of Martin Carrier’s work on incommensurability. The first commentary consists in two brief remarks by André Coret. One is about the relation between Martin Carrier’s conception of incom- mensurability on the one hand, and realism and relativism on the other hand; the other is about the identification of incommensurability with untranslatability. The second commentary is a discussion, by Soazig Le Bihan, of Martin Carrier’s reconstruction of incommensurability. Soazig Le Bihan investigates the logical relations between three terms: inferential rela- tions, conditions of application and the clause “the set of situations to which a concept is properly applied”. She questions the independence and the symmetrical role of the two former in the determination of mean- ing, and she then argues that the chief criterion of meaning and transla- tion should be the third. Finally, she suggests that a more adequate and sound reconstruction of incommensurability could be achieved in shift- ing from semantic theory of meaning to semantic theory of science. In the later framework, semantic incommensurability would be defined as an (at least partial) incompatibility as regard to internal structure (non congruence of the models of the theories). The third commentary is a exam, by Léna Soler, of the way Martin Carrier uses the two conditions ‘sameness of conditions of application’ and ‘preservation of inferential relations’ in order to reconstruct incom- mensurability. I argues that two different senses of ‘conditions of applica- tion’, and correlatively two different understandings of the clause ‘trans- lation according to preservation of inferential relations’, are involved in Martin Carrier’s analysis of historical cases, and that once these senses are distinguished, the seductive symmetric conclusion of Martin Carrier does no more hold. Hoping to contribute to Martin Carrier’s general project by complementary means, I introduce more fined-grained dis- criminations and try to clarify some central difficulties. In Martin Car- rier’s paper these difficulties take a particular form, but in my opinion, they manifest fundamental difficulties inherent to any holistic-contextual The incommensurability problem 27 framework — and thus difficulties that will appear inevitable to anyone thinking that holistic and contextual features are essential features of scientific practices. On the basis of these distinctions and analyses, I investigate the links between conditions of application and inferential relations and, finally, sketch an alternative characterization of semantic incommensurability in which the ‘inferential relations’ determinant ap- pears as the central and primary determinant (from a methodological point of view at least). 4. Hanne Andersen starts from Kuhn last characterization of in- commensurability in terms of non homology of taxonomic structures and violations of the no-overlap principle. She argues that such a character- ization, although based on a plausible model sustained by some recent works on categorization in cognitive psychology, is nevertheless not a sufficient one to distinguish between revolutionary and non revolution- ary transitions. She makes propositions to complete and refine Kuhn’s characterization, by insisting on the fact that taxonomic structures are dynamical entities, and by focusing on the reasons why they sometimes drastically change. According to her, following a suggestion of Murphy and Medin, one must take into account, in order to distinguish incommensurable theories from cases of refinements and additions, not just the taxonomic structure and its given correlations of features in themselves, but, moreover, the justifications sustaining such correlations. These justifications are given by the theories underlying the conceptual framework. Indeed, the ac- cepted explanations involved in theories, at the same time determine the bundling that organize previously encountered cases, determine which combinations are in principle possible and thus empirically expectable (even if they have not been actually empirically encountered at this point of the inquiry), and determine which combinations are in principle ruled out. Only such theoretically impossible combinations would, if empiri- cally encountered, constitute a severe anomaly. The integration of such an anomaly would call the conceptual structure into question. It would lead to a deep restructuration of the previous taxonomy, corresponding to new bundlings of features, new divisions, new categories, new ob- jects. In other words, we would have a case of incommensurability: the case of two unsuperimposable structures coordinated with two mutually exclusive theoretical systems and two mutually exclusive ontologies. Although achieved by non identical trajectories and analytical means, Hanne Andersen’s last conclusion is perfectly congruent with Martin Carrier’s one when attempting to characterize the specific kind of con- trast that is responsible for incommensurability. Hanne Andersen also 28 Introduction suggests a way to clarify the same difficulty, inherent to the incommen- surability problem, that, as we have seen, Carrier examined too: the difficulty, described as “a serious challenge that has shown very difficult to handle”, “to explain how theories that are incommensurable theories can nevertheless compete”. Non-competing theories, equated with theories pertaining to sepa- rated disciplines or specialities, could be called ‘incommensurable’ in a more strict and radical sense than competing theories (and Kuhn some- times called the first ones ‘incommensurable’). But then it seems that they would be incommensurable precisely because they are not ‘about the same thing’ (or to put it metaphorically, following Kuhn’s and An- dersen’s imagery: because they are theories occupying separated niches). By contrast, rival theories like Newtonian and Einsteinian physics are conceived as theories targeting the same object. For this reason it seems at first sight that they could be incommensurable in an epistemologically consequential sense. But can they really be incommensurable in a strong sense, since they must target something like the same domain? Andersen’s proposition in order to distinguish these two cases and to tackle the associated difficulty is the following. We have a case of incom- mensurability in Kuhn’s original sense, that is, a case of incommensu- rability between rival theories, if and only if the two theories involved, although being differently structured, bundle (at least some) shared fea- tures. “While it is shared structure and not shared features that yields shared ontology, when structure is no longer shared, it is shared features that provides the overlap between different phenomenal worlds necessary for them to compete in offering the better account of the world in the form of more successful or more promising bundlings”. 5. Aristides Baltas is, at a point, led to the same difficulty, but the spirit of his project, and the picture emerging from it, sounds differ- ently, although there is maybe no contradiction at the level of general thesis. The project is to reformulate and clarify incommensurability in a wittgensteinian framework. Aristides Baltas puts at the center what he calls the “grammatical resources of the paradigm”. The grammatical resources refer to a set of ‘assumptions’ with quotes, where the quotes indicate that the assump- tions in question are, within a given paradigm, not identified or expressed as such, or at least not subject to discussion, to justification, to test pro- cedures or the like. Remaining tacit or not questioned, it is silently that they perform their work. This work is inextricably semantical and methodological. The considered ‘assumptions’, at the same time consti- tute “the latent part of meaning” and channel the investigation process. The incommensurability problem 29

They give its usual or natural interpretation to the conceptual system coordinated with the paradigm. They underlie the favored analogies and pictures. They determine what is possible and impossible, waited or unexpected, obvious or questionable, important or anecdotic, given or open to test. . . All this constitute a grammatical space, with its potentialities and its bounds. In such a framework, radical scientific change is described as a “leap into the ungrammatical”. This happens through the following pattern. In the course of the investigation of nature by the characteristic means of a given paradigm, deadlocks arise and resist. Then at a point, sci- entists (or at least some of them) become convinced that the only way to overpass the problems is to turn the deadlock into a definition. In other words, they now admit what was previously unacceptable and most of the time unthinkable, or at least unthought, precisely because it was out of the grammatical bounds of the paradigm. In this move- ment, some previously hidden ‘assumptions’ are disclosed. They become illuminated, they are suddenly viewed as assumptions without quotes, transformed into propositions subject to discussion and test. The work they surreptitiously performed before is now rendered explicit. What they previously induced and forbid is now clarified. On the whole, a new and broader grammatical space is opened. A new vantage point is thus available. From such a new vantage point, the assumptions constitu- tive of the old paradigm appear, ex post facto, as unawares unjustifiably presuppositions, and correlatively, the anomalies having led to the rev- olution appear as misconstructions due to the work of old illegitimate pre-judgments. On the basis of such a reading of incommensurability, Aristides Baltas intends to show that the ideals of rationality and scientific progress can be saved from the accusations of relativism recurrently directed against Kuhn’s work, and that some varieties of realism are compatible with kuhnian inspired positions. In order to achieve that aim, he analyzes anomalies as resistances originating in a world independent of ideas and forcing scientists, be it only negatively, to recognize the inadequacy of their current paradigms. He examines the very nature of the communication breakdown between scientists residing in incommensurable paradigms, arguing for its in- evitability, but pointing at the same time available means to cope with it, relying on the large amount of common assumptions. Indeed there is, argues A. Baltas, a kind of continuity between suc- ceeding paradigms. First, the two parties share an enormous grammat- ical space and large areas of common language: there are blind spots, 30 Introduction but these are circumscribed. Second, two competing paradigms are never totally unrelated. A scientist having experienced a revolutionary tran- sition and living now in the new paradigm is always able to spell out significant relations between the old and the new paradigms — espe- cially in the case of mathematical physics. A. Baltas sketches an analysis of the potential corresponding conceptual, empirical and mathematical relations. He talks about imperfect and fragmentary translations and (re)interpretations, or sometimes about “interpretation/translation” in order to indicate that his use of the word “translation” is not the specific one retained by Kuhn in his late characterization of incommensurability as non-translatability [Kuhn 1983a]. Among significant relations that can be spelled out between two succeeding paradigms, we find an impor- tant one targeting phenomena. Indeed — and third, a sense has to be given to the idea that the two parties share identical phenomena to be explained, even if it is not strictly correct to talk about the same phe- nomena tout court. We have to admit that “something of the materiality of the phenomena (. . . ) is carried invariant across the leap”. Otherwise we are no more able to render justice to the shared assumption that the old and the new paradigms are competing paradigms — here we encounter one more time the difficult question, enounced in the general presentation above and also faced by Andersen’s paper, of giving sense to the idea that paradigms are at the same time rival and incommensu- rable. According to A. Baltas we have to admit — with qualifications — that the new paradigm “capture the same ‘something’ that resisted its capture by the old” paradigm. This is what “makes the new paradigm not merely different from the old, but the one that succeeds it”. On the whole, the new paradigm conserves somehow, at different levels and notably at the level of phenomena, the memory of the old. The post-paradigm continues to enfold the impossibilities of the pre- paradigm to cope with determined anomalies, even if, by construction, it enfolds these impossibilities under the form of a “repressed memory”. “In repressing this memory, it resolves the anomaly and becomes the grammatical space of a new paradigm; but still enfolding it, it remains linked to the old and thence continuous with it in this sense”. Such a continuity constitutes, joined with a claim of asymmetry that we are going to consider now, the support of A. Baltas’ claim accord- ing to which incommensurability is perfectly compatible with scientific progress. The pre- and post- paradigms, he insists, are not at all in an equivalent position. On the contrary, there is an inherent asymmetry between them. To analyze the nature of such asymmetry shows that the post- is objectively superior to the pre-. The incommensurability problem 31

The succeeding paradigm is, first, objectively wider than the preced- ing one. Indeed, more is thinkable and visible in it – and this holds inde- pendently of any claim concerning its empirical adequacy. From the new vantage point P2, The post-revolutionary scientists are aware of assump- tions that remained unseen or unquestioned by the pre-revolutionary scientists. They can show how these assumptions assured the coher- ence of the old conceptual system. They can render explicit what these assumptions suggested and what they forbid. They can give reasons concerning why it was questionable to endorse them. . . Whereas the pre- revolutionary scientists cannot, remaining blind to these assumption and a fortiori to their effects. Hence, the sort of ‘interpretation-translation’ involved here is a “one way” interpretation-translation, only performable from the new to the old. The new grammatical space, the new horizon of the inquiry, is thus objectively wider than the old one. As a particular case, it is wider as well at the level of evaluations of empirical adequacy/non-adequacy. Post-revolutionary scientists have at their disposal explanations spelling out why old scientists encountered certain empirical anomalies and were not able to overcome them. They can give reasons for the success and failure of the way P1 accounted for its empirical phenomena, and they are able to account successfully for at least some phenomena (as reinterpreted) that were at the heart of the deadlocks having originated the revolutionary change. Whereas adherents of the old paradigms do not have symmetric means at hands: they remained blocked. The former has the advantage on the latter, also at the level of “rhetorical ammunition”. The former possess objectively powerful means than the later in order to convince of the superiority of their viewpoint. They have thus more chances to succeed than their adversaries. Moreover, the involved asymmetry induces a strong irreversibility. Once scientists have seen, they cannot do as if they had not seen. There is no possibility to go back. In that sense, once a wider grammatical space have been opened, the old paradigm is definitively superseded; there is no real choice between the old and the new. The pattern just described is what constitutes scientific progress as understood by A. Baltas. Scientific progress so understood takes places intricately at both conceptual and empirical levels, and it is a genuine progress, although not a cumulative one. So far, we dealt with incommensurability in the traditional sense. Now, the two last paper of the book enlarge the perspective in consid- ering the case of the machinic-literal incommensurability. 32 Introduction

6. Michel Bitbol considers the incommensurability problem in a neo-pragmatic and structural perspective. This perspective is funda- mentally sympathetic to Wittgensteinian insights, although these are not explicitly mentioned in the article. Michel Bitbol urges the incomplete- ness of the linguistic-based account of incommensurability, and argues for the fruitfulness of an explanation that equates the technico-experimental practices, and more generally the performative aspects, with the central axis of physical knowledge. He is then led to discuss machinic-literal incommensurability. He begins in distinguishing three strata within a physical paradigm: the ontological, the performative and the structural ones. The ontologi- cal stratum is associated with models, representations, physical scenarios or stories (it is, in other words, the narrative side of high-level theo- ries). The performative stratum names the instrumental and behavioral culture characteristic of a laboratory tradition (including the technico- experimental knowing-how, the specific goals of concrete realizations and so on). The structural stratum designates the mathematical formalism and the associated legal-predictive potentialities of high-level theories (such a formal skeleton being possibly the common core of a range of different and incompatible ontological interpretations and models). From there Michel Bitbol stresses two points. 1/ All is not linguistic, verbalised and explicit in the paradigm, especially at the performative level: here in particular, the philosopher must take into account com- mitments and projects, backgrounds norms of action, acquired habitus, entertainment to act in certain ways, knowing how, tacit background knowledge, etc. 2/ Although the three strata are in fact related, each of them have a certain non negligible autonomy. These two points constitute the basis on which Michel Bitbol de- velops his conception of a non linguistic kind of incommensurability: an incommensurability of laboratory practices inspired by the work of Pick- ering and Hacking, also labeled “performative incommensurability” since it primarily concerns the performative stratum37.

37“Performative incommensurability” is an expression first introduced by A. Pick- ering. But in his paper, M. Bitbol uses the expression in a quite different sense than Pickering’s original one. In Pickering text, “performative incommensurability” names the possibility of an extreme form of incommensurability, in fact just sketched but not really explored. This possible incommensurability would involve more exotic practices than the scientific ones. It have been for this reason let aside in the general presentation above, but here is an occasion to mention it. Pickering talks about “the possibility of a radical performative incommensurability — an incommensurability of powers” [Pickering 1995, 245], an “incommensurability in human (and non human) powers” [Pickering 1995, 192], residing in the contrast The incommensurability problem 33

Such an incommensurability of laboratory practices may happen in the absence of any incommensurability at the structural-ontological lev- els: it may happen between scientific practices sharing a lot structurally and ontologically — the possibility of this disconnecting being opened by the relative autonomy of the three layers. Correlatively, such an in- commensurability cannot be grasped through an exclusively-linguistic characterization — due to the non verbal and implicit constitutive as- pects of laboratory practices. Incommensurability of laboratory practices names the relation be- tween two highly different forms of laboratory life: between laboratory cultures that are organized by very different background presuppositions and that involve mutually exclusive gestures, experimental setups, exper- imental configurations and results. M. Bitbol gives two examples. The example of two laboratory traditions in high-energy physics, the first one being governed by a culture based on images (produced via bubble chambers etc.), and the second one by a culture of counting (electronic detectors like scintillation counter, spark chambers etc.). And the ex- ample of experimental chemical practices before and after Lavoisier, the second one conferring a crucial advocating role to scales, whereas the first one takes such procedures as non crucial, non significant or sometimes even irrelevant. Reading Michel Bitbol’s developments, it appears that such labo- ratory traditions are autonomous in several senses. First they are au- tonomous with respect to one another as well as to higher-level theo- retical strata, in the sense of possessing proper internal characteristics and having relatively independent internal conditions of coherence and closure. But they are moreover autonomous in a stronger sense with respect to high-level theories: they are credited of having the power to be (sometimes) the driving force of important changes at the higher between standard and non standard performances. “None of the studies I have dis- cussed involve much more of human beings than observing what is going on and manipulating medium-size objects in humdrum ways”. But in some cultures we find “non-standard material agency, (. . . ), stories, for example, of mines inhabited by dwarves, demons (. . . ). On the other side, we also find human beings with quite non-standard powers — magi, alchemists, witches, and so on” [Pickering 1995, 243]. “Within different cultures human beings and the material world might exhibit capac- ities for action quite different from those we customarily attribute to them”. “The question remains of whether we should think it”, but “that our own powers as human beings might be bound up with culture in this way is a quite startling idea that I find it fascinating to dwell upon. It is, of course, absent from traditional discussion of incommensurability” [Pickering 1995, 245]. Bitbol “performative incommensurability” is closer to what Pickering names “ma- chinic incommensurability”. 34 Introduction structural and ontological levels (and as a particular case, of having the power to impulse the development of incommensurable theories). This may happen when they presuppose, most of the time tacitly, assump- tions and characteristics which prove to be in tension or disharmony with some central assumptions of the theoretical levels. In such a situa- tion they contain, in a way potentially, the power to destabilize higher strata, or in other words the seeds of theoretical revolutions. And that sometimes indeed happen. Thus high-level explicit theories and high- level (in general less explicit) values governing theoretical elaboration, are not, as some philosophers of science have often assumed, the only or the primary actual driving vector of scientific changes. Michel Bitbol’s paper develops such ideas in association with other claims that have consequences for the incommensurability problem. Ac- cording to him and to many neo-pragmatic thinkers, traditional dual schemes putting face-to-face a knowing subject and a preexisting object, or a proposing-scientist and a nature-thing, or theories and phenomena or the like, have to be replaced by a co-production scheme according to which the two poles of each duality are nothing more and nothing less than the meta-stable products that have co-emerged from an internal- to-practices dialectical process. Following [Hacking 1992], M. Bitbol emphasizes moreover that in such a neo-pragmatical perspective, the classical Duhem-Quine under- determination of scientific theories has to be enlarged in principle, so as to include the new elements of experimental practices (notably the material and performative ones) that have been recognized susceptible to enter into the possible infinite combinations constituting empirical co-adjustments. He militates in favor of the notion of a generalized co- herence that would apply not only to ideas or propositions, but also to concrete actions. But he recalls at the same time with Hacking that we need to reflect, correlatively, on the reasons why the feeling of under- determination is so reduced in practice. Finally he examines the tempta- tion to maintain certain form of realism in such a framework, grounding the reflection on the new epistemological situation offered by quantum mechanics, and extending it to the case of mathematical practices. 7. In his paper Emiliano Trizio intends, for his part, to clarify the relations between two forms of incommensurability that are con- sidered to be intrinsically different. The first one is the ‘traditional’ kuhnian incommensurability identified with taxonomic untranslatabil- ity. The second one is the machinic-literal incommensurability intro- duced by Hackingand Pickering, and presented by them as a new form The incommensurability problem 35 of incommensurability having nothing to do with meaning change and untranslatability (cf. above). According to Emiliano Trizio, taxonomic and literal incommensu- rabilities, far for being two different in nature, well separated episte- mological configurations, are, rather, two particular species of a generic super-ordinate characterization of incommensurability describable as “an enlarged taxonomic version of incommensurability”. In order to argue for this thesis, Emiliano Trizio provides a deep analysis — notably inspired by Pierre Duhem’s and Nancy Cartwright’s discussions of the (often instrumented) relations between theory and ob- servation — of what we may mean when we say that scientific terms “apply to nature”. He urges fine-grained discriminations between differ- ent kinds of applications to the world. The aim of such discriminations is, above all, to capture and highlight what he takes to be an essential difference: namely, the difference between applications that involve in- strumented acts of measurements and applications that are exempt of such kind of acts. Kuhn is accused to remain blind to such a difference especially in his latest works, this blindness being manifest in Kuhn’s uniform treatment of all scientific examples, regardless of the degree of abstraction of the theories and of the degree of sophistication of experi- mental activities involved. Let us reconstruct Emiliano Trizio’s own position. The philosopher of science reflecting on modern physics should pay more attention to the difference between perceiving and measuring. Indeed, unaided, normal perception and highly instrumented cognitive activities involved in ex- periments are two different kinds of acts of the knowing subject, two performances that have an “intrinsically different status”. There are, correspondingly, two kinds of terms or, if one focuses on structured clus- ters of terms, two kinds of taxonomies: terms or “taxonomies that can be applied perceptually”; and terms or “taxonomies that require acts of measurements”. Consequently the “ostensive/non ostensive character” of a theory is introduced, or more realistically — shifting from sharp contrapositions to a continuous scale of ‘ostensiveness’ — the degree of ‘ostensiveness’ of a theory, that is, its “degree of perceptual accessibility”. Moreover and correlatively the idea — central for the suggested enlarged conception of incommensurability — of dual/non-dual taxonomies is for- mulated An example of non-dual taxonomy is a “perceptual” or “observational” taxonomy, the most obvious example being the “common-sense” tax- onomies underlying ordinary observations (but “descriptive sciences” are also mentioned), which involve only “ready-for-use” terms: only terms 36 Introduction that are, in a given context, immediately applicable on the basis of an act of unaided, normal perception. By contrast, a dual taxonomy moreover contains terms that are split into different sets in turn linked to disparate specific instrumented conditions of application. Taxonomies of contem- porary physics, or taxonomies of any physico-mathematical theory, are dual. A dual taxonomy is called “dual” because it is composed of two parts (or two “semi-dual taxonomies”): the “experimental part” and the “objec- tive part”. The experimental part is composed by names and descriptions targeting different sets of instrumented experiments: each of these sets being “the class of equivalence of all possible experiments leading to the same conclusion (conceptually unified by physical theory)” which “can in turn be divided in types of experiments”, subtypes etc. The “objective part” of the dual taxonomy is composed by descriptive terms purporting to refer to the world (is only composed by “objective terms” referring to reality). The two parts of the dual taxonomy are “highly interrelated”. Roughly speaking, the types of laboratory practices constituting the experimen- tal part define the appropriate conditions of application of the objective terms. The relation between the two components is more exactly de- scribed as a relation of “co-classification” (“the entities physical theory describes are classified if and only if the experimental contexts that reveal them are classified in turn”), or as a relation of “co-subsumption” on the one hand of what is equated with objective entities and processes, and, on the other hand, of actions in experimental contexts. In other words, the interrelation is of the following nature: experimental actions aim at measuring physical objective quantities; and reciprocally, physical the- oretical quantities supposed to refer to physical objective unobservable realities cannot be recognized as such without performing experimental actions and assuming the relevance and reliability of these actions. Now, assuming the relevance and reliability of these actions amounts in turn to be committed to assumptions that order the available experimental activities in classes taken as equivalent with respect to the determination of the targeted physical quantities and that give a definite particular content to the methodological condition of the repeatability of the ex- periments. An inverse proportionality holds between the ostensive strength of a theory and the dual character of its taxonomy. In the case of descriptive sciences, the experimental part of the dual taxonomy is most of the time embryonic if not null, whereas in contemporary mathematical physics, it is hypertrophic (the last point being illustrated in the paper through The incommensurability problem 37 the case of the crystalline lattice structure). The role of perceptual similarities is very reduced in mathematical physics: the dual taxonomy groups into equivalent classes — via the experimental part — infinitely different perceptual features. Linking the latter reflections and distinctions to the theory-learning process , it appears that we have to take into account a “hierarchy of increasingly concrete and quantitatively defined exemplars” in Kuhn’s sense of the term, some of which include experimental instrumented actions in the laboratory. However, to learn theories by solving paradig- matic problems through expositions to (more or less ostensive and dual) exemplars, does not amount to ‘genuinely apply scientific terms to na- ture’. Kuhn conflates learning or understanding a theory (by solving problems with a pencil and a sheet of paper) with “applying it to the world” (and he mainly focused on the first activity, more and more exclu- sively characterized in terms of linguistic differences). But the authentic application of a theory to the world only takes place during a real lab- oratory session involving the recognition that what happens before our eyes is the situation described (in an idealized and purified way) in the textbooks. Now, very talented skilful problem-solvers may be completely lost in a well-equipped laboratory. Thus on the whole, dealing with the application of scientific concepts to nature, we have to take into account, not only degrees of concreteness of the exemplars, not only degrees in the extension of the experimental part of dual-taxonomies but, moreover and above all, degrees of acquain- tance. Authentic application requires the coordination of (more or less ostensive, more or less dual) scientific taxonomies and exemplars with indeed experienced concrete (instrumented in the dual-case) situations. Relying on these distinctions Trizio claims that an “enlarged taxo- nomic formulation” of incommensurability can be defined. “Incommen- surability results, in general, from a deep transformation of the taxon- omy pertaining to a theory, where the term “taxonomy” can refer both to dual taxonomies and to more descriptive ones. In the case of lab- oratory science, this transformation implies the replacement of a dual taxonomy with a new, incompatible one”. In such framework, Hack- ing’s and Pickering’s versions of incommensurability on the one hand, and Kuhnian incommensurability on the other (illustrated through the example of Ptolemaic/Copernican astronomies), can be equated to two particular extreme cases of such “enlarged taxonomic incommensurabil- ity” in the spectrum of “an ideal classification of theories with respect to the strength of their ostensive character and the inversely proportional duality of their taxonomies”. 38

Hacking’s and Pickering’s cases correspond to “theories that differ radically not only with respect to the objective part of their dual tax- onomies, but also with respect to the experimental part”. In other words, they involves “two rival schools of physicists accepting different dual tax- onomies that define distinct classes of equivalence of experimental set- tings and procedures”, so that the “two rival theories are supported by disjoint sets of measurement procedures”. Between such a configuration and Kuhn’s example concerning Ptole- maic/Copernican astronomies, all intermediary cases may be conceived (although their plausibility remains to be examined): all combinations that may be generated from the idea that only some elements are not shared in the objective and experimental parts of the dual taxonomies.

8. The bibliography at the end of the volume contains the refer- ences mentioned by each contributor in his own paper, plus a selection of references about the incommensurability problem that takes into ac- count the descriptive, axiologic and machinic dimensions. Given the impressive volume of the literature devoted to incommensurability and the space allowed, it has been impossible to provide the reader with a complete bibliography. I emphasized recent works and tried to include all the major classical references38.

38I am particularly grateful to Alexander Bird and Emiliano Trizio for helping me by their critical comments and their remarks concerning the English language; I am further indebted to Paul Hoyningen-Huene, Howard Sankey and Scott Walter who read and commented parts of this introduction. Kuhn on Reference and Essence

Alexander Bird University of Bristol

Résumé : La thèse kuhnienne de l’incommensurabilité semble mettre en cause le réalisme scientifique. Une réponse à cette mise en cause consiste à se focaliser sur la continuité de la référence. La théorie causale de la référence, en particulier, semble offrir la possibilité d’une continuité de la référence sus- ceptible de fournir une base pour l’espèce de comparabilité entre théories que requiert le réaliste. Dans « baptiser et rebaptiser : la vulnérabilité des dési- gnations rigides », Kuhn attaque la théorie causale et l’essentialisme auquel cette théorie est liée. La position de Kuhn est défendue par Rupert Read et Wes Sharrok [Read & Sharrok 2002b]. Dans cet article, j’examine les argu- ments présentés par Kuhn, Read et Sharrok, et je montre qu’ils ne fournissent aucune raison de douter ni de la théorie causale, ni de l’essentialisme. Abstract: Kuhn’s incommensurability thesis seems to challenge scientific re- alism. One response to that challenge is to focus on the continuity of reference. The causal theory of reference in particular seems to offer the possibility of continuity of reference that would provide a basis for the sort of comparability between theories that the realist requires. In “Dubbing and Redubbing: The Vulnerability of Rigid Designation” Kuhn attacks the causal theory and the essentialism to which it is related. Kuhn’s view is defended by Rupert Read and Wes Sharrock [Read & Sharrok 2002b]. In this paper I examine the ar- guments presented by Kuhn, Read, and Sharrock and show that they provide no reason to doubt either the causal theory or essentialism.

Philosophia Scientiæ, 8 (1), 2004, 39–71. 40 Alexander Bird 1. The challenge of incommensurability and the ref- erentialist response

Kuhn’s incommensurability thesis tells us that there is an important difficulty in translating between the scientific terminology of theories from either side of a scientific revolution. Even where the terminology looks the same — the same words are employed — their meanings have changed, so that they no longer express the same concept. Considered as two homophonic terms, the one term does not translate the other. Prima facie this is unwelcome to realists. One of the ways in which science progresses is by correcting the mistakes of earlier scientists. We once thought the Earth to be at the centre of the universe, orbited by the planets, whereas we now know that the Earth is not at the universe’s centre, but is itself a planet orbiting the Sun; it was once thought that water is an element, but we have since discovered that it is a compound; the idea that new species have evolved has displaced the old mistaken view that species are immutable. And so on. But if the new theories and those they replace do not mean the same things by the terms they use, it looks as if we cannot straightforwardly say that the later theory denies what the earlier one asserts, in which case we cannot say that it represents a correction to and improvement on the earlier theory. However, on further reflection the realist does have a way of defend- ing the idea that later science genuinely corrects (and so rejects) some parts of earlier science. The realist can say that whatever else may have changed, the reference of the key scientific terms has remained constant. We use our scientific terms to talk about things, kinds, properties, quan- tities and so forth. This ‘talking about’, a relationship between words or phrases and things in the world is the relationship of reference. And ref- erence is what is important to truth (and falsity). For it is the properties of the stuff water that determine whether or not it is an element. Conti- nuity of reference therefore allows later scientists to say things that are incompatible with what earlier scientists had said, where ‘incompatible with’ means ‘not true at the same time as’. Boerhaave used the term ‘aqua’ in his Elementa Chemiae (1732), Lavoisier used ‘eau’ in his Traité élementaire de chimie (1789), and Berzelius used ‘vatten’ in his Lärboki Kemien (1808-18 to 1843-48). They ascribed different and incompatible properties to what they were talking about. Various accounts of ref- erence makes it both possible and plausible that nonetheless they were referring to the same substance and hence that the later chemists were able to correct their predecessors. Kuhn on Reference and Essence 41

The idea that reference is a key concept in assessing the progress of science and that there has been a large measure of referential continuity over time, even over revolutions, I shall call referentialism. Although it is not their view, Read and Sharrock nicely encapsulate the importance of referentialism to realism thus:

There is only one world, and the Realist (unlike the Relativist or Idealist) can have coherent things to say about our deepening knowledge of that (one) world, because we (all of us, especially via scientists) are always in touch with the world. We are in touch with it through our naming of bits of it, and our growing knowledge about the nature of what we name. It may that at different times people had radically wrong ideas about the nature of the world — they may have thought, for example, that water was a primitive element — but, through being in contact with bits of the world (e.g. with water), and through naming it, they always had some kind of ‘basis’ to their claims. We can connect with them and what they said, because there are direct (albeit long) chains of connection — linguistic and (more generally) ‘causal’ — between their use of these words and our use of them. They may have ‘meant’ something very different by their words, but the reference of their words was just the same as our reference for the same words. Reference — and in particular a causal theory thereof — will settle the problem which meaning poses. [Read & Sharrok 2002, 153].

If referentialism is correct, the challenge presented by Kuhn’s incommen- surability thesis is rather weaker than at first appeared. As Read and Sharrock continue, the realist thinks that ‘Kuhn is wrong, because he thinks that incommensurability of meaning is important and deep. It is, in fact, completely shallow and unimportant, once one understands that the real reference for natural kind terms remains continuous over time and through ‘revolutions’.’ Given such a consequence for Kuhn’s thesis, it was natural that Kuhn should reject referentialism. Kuhn thus argues against it in his paper “Dubbing and Redubbing: The Vulnerability of Rigid Designa- tion” [Kuhn 1990a] and his view is defended and elaborated by Rupert Read and Wes Sharrock [Read & Sharrok 2002]. This paper aims to defend the referentialist view expounded above so very clearly by Read and Sharrock against the criticisms that they and Kuhn level against it. They also criticize the related thesis of essen- tialism, and I shall also defend this. The aim of this paper is thus not to criticize Kuhn’s incommensura- bility thesis. Rather it is to show how the referentialist and essentialist can mount an effective defence against the specific criticisms of Kuhn, 42 Alexander Bird

Read, and Sharrock. If such a defence is successful, then the thesis of incommensurability may be thought to present no interesting challenge to the realist. The realist can regard incommensurability and realism as consistent. Of course, there are other reasons one might have for doubting realism, and these may even be part of a more broadly Kuh- nian framework. These issues will not be my concern here. My concern is limited to articulating a defence of the referentialist versions of real- ism against the specific criticisms raised by Kuhn, Read and Sharrock. Mounting this defence does not require therefore that I defend realism in general. This will be important because the referentialist defence of scientific realism against the apparent threat of incommensurability is itself thoroughly realist. For example, the referentialist defence takes it that there is a world of independently existing entities studied by science and that we are able to refer to such entities. The referentialist defence is easiest to express if we assume that scientists can get to know things about such entities, although I do not believe that this assumption is an inevitable part of the referentialist defence. That referentialism makes realist assumptions is no failing, since the context in question is the de- fence of realism, not the larger issue of whether realism is superior to anti-realism.

2 Referentialisms and essentialism

Read and Sharrock regard the position they describe as a ‘kind of essen- tialism’. This is misleading, for although essentialism is closely bound up with questions of reference, it is an entirely distinct view from ref- erentialism. A property which is essential to a kind is a property such that no entity could be a member of that kind without possessing that property1. So ‘being mammalian’ is an essential property of the kind horse since nothing could be a horse without being a mammal. Histori- cally essences have been held to come in two varieties, nominal and real essences. A nominal essence of a kind K is a property that an object belonging to the kind possesses in virtue of the verbal definition of the term ‘K’. The real essence of a kind derives instead from the nature of the kind. The presupposition of the idea of a real essence, whereby a kind can have an essential nature, is that the kind in question has a real, natural existence. One could regard some random collection as the mem- bers of some kind defined for that purpose (e.g. the kind K is defined as having exactly, the Eiffel tower, my desk, and the number nine as its

1This may only be a necessary condition of being an essence, not a sufficient one. See [Fine 1994]. Kuhn on Reference and Essence 43 only members, the kind L is defined as comprising all and only objects that are either cubes or are coloured red). Such kinds could be regarded as having nominal essences (necessarily something is L iff and only if it possesses the property of being either red or cubic). But clearly such kinds do not have a nature distinct from their nominal essences, and so they do not have real essences distinct from their nominal essences. In its most general form, essentialism is the view that there is a non-trivial distinction between essential and non-essential (accidental) properties. However, a more specific conception of essentialism takes it that there is a non-trivial distinction between real essences on the one hand and on the other hand firstly accidental properties and secondly merely nominal essences. Thus on the more specific conception there exist natural kinds with real essences and not in every case are these real essences identical to or immediately derivable from the nominal essences and the verbal definitions of the kind terms2. This kind of essentialism may be extended to incorporate real essences of natural properties and individuals also. Since the features constituting the real essence derive form the nature of a kind (property, individual) rather than from its verbal definition, and because the nature of a kind may be hidden from us, revealed only by a posteriori, scientific investigation, it may be the case, hold many essentialists, that in some instances a real essence may be uncovered only by empirical investigation and cannot be known a priori. In what follows, I shall reserve the term ‘essentialism’ for the more specific thesis, that there is a non-trivial conception of real essences. Since referentialism is a thesis about words while essentialism is a thesis about things and their metaphysics, it should be clear that they are not the same thesis. Indeed referentialism as I have characterised it is consistent with the denial of essentialism. A term ‘K’ may continue to refer to a kind K over time without its being the case that all Ks share a real essence. This is true of the artificial kinds K and L introduced above. Members of those kinds share a nominal essence but not a real essence. Referentialism per se does not require the existence of natural kinds. One reason for wanting to divorce referentialism from essentialism is that within referentialism there are different views about how reference works and while some of these are closely associated with (although not

2An essentialist of this kind might maintain that the real essence reflects a kind’s real definition. But then the real definition and the verbal definition need not be the same. 44 Alexander Bird identical to) essentialism, other views about the working of reference are not so associated. I shall discuss the two main versions of referentialism: (a) the Fregean version, employing a concept of sense which determines reference, and (b) the Kripke-Putnam version, employing a causal or non-Fregean, externalist conception of reference determination. Only the latter is closely related to essentialism.

3 Fregeanism and the first referentialist response

One way of expanding on referentialism as characterised above is to em- ploy Frege’s famous sense-reference distinction [Frege 1892]. According to this view a term has associated with it a sense (Sinn or intension). What exactly Fregean senses are or ought to be is a matter of dispute, but the following aspects of sense are central:

(i) the sense of a term determines its reference (Bedeutung, extension);

(ii) the senses is grasped by someone who understands the term in question.

A common way of thinking about sense is as a set of descriptions such that (i)* something is the reference of the term if and only if it satisfies those descriptions, and (ii)* someone who understands the term believes those descriptions to hold of the reference of the term. Of course a speaker may have many beliefs about the reference of a term she uses, and not all those beliefs will be part of the sense of the term. The beliefs associated with the sense will be true analytically and will be knowable a priori. For example someone might propose that the sense of ‘human’ is ‘rational animal’. If that is correct then since sense determines reference, all and only rational animals will be humans, and because senses are grasped by speakers, everyone who understands the term ‘human’ will believe (perhaps only tacitly) that humans are rational animals; the latter proposition will be true analytically and will be knowable a priori. One feature of the Fregean view that will be important later is a consequence of the combination of (i) and (ii). Let T1 and T2 be terms with different references. Then, by (i), T1 and T2 must have differing senses. By (ii) we may expect the beliefs of a subject with respect to the reference of T1 to be different from their beliefs with respect to T2. (Strictly, the range of analytically true, a priori known, beliefs of the subject will differ). Conversely, two subjects who are identical in all respects, differing at most in ways about which they are entirely ignorant Kuhn on Reference and Essence 45

(e.g. differing in aspects of their environment beyond their ken) will use terms with the same sense and so the same reference. The Fregean view provides a referentialist response on behalf of the realist to Kuhn’s incommensurabilist challenge. Several terms may have different senses but share the same reference. In Frege’s example, ‘Venus’, ‘Hesperus’, Phosphorus’, ‘the morning star’, ‘the evening star’ are all terms that refer to one and the same planet; but, arguably, they have different senses. This means that the realist can accept Kuhn’s claim that the meanings of terms change through revolutions so that a word used after a revolution does not translate the same word as used before the revolution. For translation requires preservation of sense. So the realist will say that there is translation failure, because sense is not pre- served through a revolution. Nonetheless, because terms with different senses can have the same reference, the reference may well have remained the same. And it is plausible to think that typically reference is indeed preserved — or at least that scientists intend reference to be preserved — because scientists very often want to add to beliefs and correct beliefs about the same things that they were previously interested in. Two things should be noted. First, the Fregean view shows that in- commensurability and referentialism (and so realism) are consistent, only so long as incommensurability is a thesis about change in senses/intensions. Were it the thesis that reference changes, then Fregeanism would be of no help. Secondly, even if incommensurability and referentialism are consistent, that fact does not prove that there is indeed continuity of reference. I shall make some remarks about each of these in turn. The precise nature of Kuhn’s incommensurability thesis is a matter of debate, not least because it changed over time. However, it is clear that it is a thesis primarily about meaning in a sense that is much closer to Frege’s Sinn than his Bedeutung. For example, incommensurability is often characterised as the thesis that terms from distinct paradigms (e.g. from either side of a scientific revolution) may fail to translate one another. Translation requires preservation of sense (Sinn, intension). So incommensurability as untranslatability is a thesis about a change in the sense of a term. The incommensurability thesis, at least in its earlier incarnation, is a consequence of the widespread theoretical-context view of the meaning of theoretical terms. The latter is also a thesis concern- ing the sense of those terms, not their reference. There are two further, related reasons for thinking that the incommensurability thesis concerns sense rather than reference. First, a corresponding thesis concerning Fregean reference (Bedeutung) is much less plausible than a thesis con- cerning sense. Prima facie, it is plausible that when there is a scientific 46 Alexander Bird revolution the shift in theories, practices and so on means that words acquire a new sense, that they cannot directly translate their predeces- sors, and that there are barriers to perfect communication. But the idea that a later theory is referring to different kinds and entities from its predecessor is much less plausible. Often, it is true, a new theory might initiate reference to an additional set of kinds and entities. So the discov- ery of the structure of DNA permitted talk of new entities (base pairs, for example). But substances being referred to beforehand were still be- ing referred to afterwards (DNA itself, for example). In other cases, old terms that failed to refer are given up (e.g. phlogiston), but in such cases also, this is against a background of continued reference (to air, water, iron, iron calx, muriatic acid, and so forth). Indeed if there were signifi- cant discontinuity in reference one would wonder why the phenomenon should be thought of as a scientific revolution as opposed to simply a change in subject matter (such as a change from physics to zoology). Since the idea of incommensurability as a shift in reference is at least prima facie implausible, it would need powerful arguments to support it. Kuhn does not provide such arguments — what he does say provides much better support for the incommensurability thesis understood as a change in something akin to sense. The second reason Kuhn would not have thought of incommensura- bility as a shift in reference is that reference (as Fregean Bedeutung) is the sort of realist notion that Kuhn either eschewed or rejected. Kuhn rejected the ideas of truth and increasing nearness to the truth on the basis that they employed an illegitimate notion of what is ‘really there’ [Kuhn 1970a]. But the function of reference is precisely to make a con- nection between our words (and thoughts) and what is really there. Now it is true that Kuhn does say the following, when discussing the common proposal that “Apparently, Netwonian dynamics has been derived from Einsteinian, subject to a few limiting conditions.”:

[T]he physical referents of these Einsteinian concepts [spatial position, mass, time] are by no means identical with those of the Newtonian con- cepts that bear the same name. (Newtonian mass is conserved; Einsteinian is convertible with energy. Only at low relative velocities may the two be measured in the same way, and even then they must not be conceived to be the same) [Kuhn 1970a, 101-102].

This passage is puzzling if Kuhn’s ‘physical referent’ is taken to be the same as Frege’s Bedeutung. For then the passage would imply that there exists in the world both of two distinct quantities, Newtonian mass and Einsteinian mass — and that Newton as talking about one and Einstein Kuhn on Reference and Essence 47 about the other. But that is implausible — why should we think that the world contains both of these two different quantities? And if there really is Newtonian mass in the world, doesn’t that mean that Newton was right after all (about ‘Newtonian mass’)? No, either there is no mass as referred to by Newton (the term ‘mass’ as used by Newton is like ‘phlogiston’ as used by Priestley) or there is mass as referred to by Newton — it is the same as the quantity referred to by Einstein, only that Newton had some false beliefs about it (the term ‘mass’ as used by Newton is like ‘Mars’ as used by Ptolemey). This passage becomes much less puzzling if we do not take ‘physical referent’ as Bedeutung, but rather to mean something like ‘what scientists took themselves to be referring to’ or ‘what scientists believed about the intended reference’. This would give us an ‘internal’ sense of reference, so that in this sense a term can have a physical referent, even if there is no physical quantity in the world corresponding to it. Furthermore, the ‘physical referent’ of a term, in this sense, will change if there is a theoretical shift (for the simple reason that what scientists believe about the intended reference changes). It might be that Kuhn thinks of incommensurability as a change in ‘reference’ understood in this sense. But then the incommensurability thesis does not, on its own, represent any threat to scientific realism (which is the issue under discussion), for the realist can accept that there is a change in ‘physical referent’ understood in Kuhn’s internalist way (just as the realist can accept a change in sense) while continuing to assert that there can be continuity in reference to a genuine quantity or entity in the world. It is important to be clear about what the referentialist claims the Fregean position would show, if true. It shows that it is possible for sense to change (leading to untranslatability) while reference is preserved. It does not guarantee that reference is indeed preserved. There could be cases where the sense associated with a term T at some time deter- mines reference R1 but after a revolution the sense associated with T has changed and now picks out a different entity, R2. Thus the Fregean version of referentialism is consistent with the view that there is discon- tinuity of reference. Therefore, all that the Fregean view would show, if correct, is that continuity of reference and so scientific realism are consistent with incommensurability (interpreted as a shift in something like sense). The appeal to Fregean referentialism is thus only a defence against an incommensurabilist critique of realism; it does not on its own show that the realist view must be correct. Could the incommensurabilist critique be supplemented to show that revolutionary shifts in intension are also accompanied by shift in refer- 48 Alexander Bird ence? I have already suggested that any argument to the effect that there are shifts in reference would have to be more powerful and de- tailed than anything Kuhn has supplied. I shall return to the issue of reference shifting later at the end of §4. More plausible on a Kuhnian version of Fregean referentialism is that there will reference failure rather than discontinuity of successful reference.

Consider the possibility that the sense of T at time t1 involves very many beliefs — {B1}. As a result of a revolution the sense of T changes significantly, so that at a later time t2, the beliefs — {B2} — constituting the sense of T are very different. Since the sets {B1} and {B2} are both large and significantly different, there is a considerable danger that the same things will not satisfy both sets, and hence that reference is not preserved. Even so, this will not involve a genuine shift in successful reference. If the earlier set {B1} is large, constituting most or all of the scientists’ beliefs about T at t1, then there it is likely that nothing will satisfy {B1} and so T has no reference and T will not exist. And indeed we may expect this to be the case, since we are interested in scientific revolutions. Given that there is a revolution involving a change in beliefs, precipitated by anomalies or other kind of failure of the scientists’ beliefs at t1, that suggests that indeed the beliefs {B1} cannot all be true, in which case T cannot refer.

This outcome, whereby there is reference failure (as opposed to shift in successful reference) is the result of combing a Fregean view with the contention that the sense of a term is very ‘thick’, involving a large number of beliefs. What is significant is that during the period preceding the writing of The Structure of Scientific Revolutions, the standard view about the meaning of scientific terms was that all parts of a theory in which a term is employed contribute to its meaning. So all the beliefs encapsulated in a theory would contribute to the term’s sense, making it very thick indeed.

In so far as we are still concerned with genuine, external reference, such a position is unattractive. It is unattractive to the realist, since widespread reference failure is in tension with the initial characterisation of realism as being committed to the improvement in beliefs about the same things. (At the same time is also incompatible with the view that there are shifts in genuine external reference. But this position need not be unattractive to the ‘internal reference’ view discussed above). So for the realist, the Fregean version of referentialism ought optimally be supplemented with arguments as to why the sense of the relevant Kuhn on Reference and Essence 49 scientific terms is likely to be thin and not thick3. It is worth pointing out that the Fregean view had troubles of its own. One source of trouble was Quine’s influential argument that the analytic-synthetic distinction is empty. If Quine were right the whole notion of Fregean sense is misconceived, for one could not distinguish between those propositions or beliefs that constitute the sense of a term and those that do not. A rather different source of trouble for the Fregean view came from Kripke and Putnam [Putnam 1975a] [Kripke 1980]. Read and Sharrock suggest that they developed their ideas ‘in part specifically in opposition to this idea of Kuhn’s’. (The idea of Kuhn’s in question was that the world changes as a result of a scientific revolution, which can be understood as the claim that scientific revolutions generate taxo- nomic incommensurability). Although Putnam and Kripke did not have world-changes or incommensurability as their primary target when they formulated their views, it is true that they and realist philosophers of science who were interested in such matters realised the significance of this version of referentialism.

4 Kripke, Putnam, and the second referentialist re- sponse

What Kripke and Putnam were primarily concerned to combat was the combination of the central Fregean claims, (i) and (ii) above. They held that it is not the case that reference is determined solely by ‘what is in the head’ of a speaker, such as the speaker’s beliefs. Hence nothing can satisfy both (i) and (ii), and so reference is not fixed by a Fregean sense. This is established by Putnam’s famous twin-earth argument. The key idea is that it is conceivable that two subjects O1 and O2 can be internally exactly alike yet when O1 uses a term T it has a reference that is different from the reference of the same word T used by O2. What does differ between O1 and O2 is their environment — but the differences in their environments are differences of which they are unaware. Thus it would appear that a set of beliefs or a Fregean sense is not sufficient to fix reference. Something else, something external to O1 and O2, something in their environment of which they are ignorant, plays a part also. In Putnam’s argument we consider two worlds E and T E. E is the actual world while T E is a world exactly like E, except that where E has H2O T E has a distinct compound XYZ that nonetheless shares the same

3For a detailed discussion of the relationship between Fregean intensionalism and incommensurability, see [Bird 2000, 163-178]. 50 Alexander Bird superficial qualities as H2O (smell, taste, boiling and freezing points, ability to support life, etc.). Consider the year 1950. O1 uses the term ‘water’. In so doing O1 refers to H2O but not to XYZ (it is a truth about the actual world that water is H2O, and not XYZ). Since E and T E are symmetrical we must say that O2 in T E when using the term ‘water’ refers to XYZ and not H2O. Ex hypothesi E and T E are alike except for the difference between H2O and XYZ. And so whatever O1 believes concerning what he calls ‘water’ O2 also believes, concerning what he calls ‘water’. So their beliefs about ‘water’ do not distinguish them — they both believe that the following sentences are true: ‘water is important for life’, ‘rain and snow are constituted from water’, ‘sodium chloride dissolves in water’ and so forth, and there is no sentence such that one believes it and the other does not. If Fregeanism were true, then the sense of ‘water’ used by O1 and the sense of ‘water’ used by O2 must be the same — by (ii) in §3 above. And so, by (i) the references must be the same. But we have seen that the references are not the same. So Fregeanism is false.

The question is then raised, what is it that fixes reference if it is not a Fregean sense, if it is not a set of beliefs in the head of the speaker? A common answer, but not the only possible answer, is that it is some kind of causal connection between the speaker’s use of the term and the reference. Why is it that when using the term ‘water’ O1 refers to H2O but not to XYZ, while O2 refers to XYZ but not to H2O? The suggested answer is that O1 is causally connected to H2O but not to XYZ and vice-versa for O2. O1 acquired the use of the term ‘water’ when as a child his parents said ‘this stuff is water’ pointing to the stuff coming out of the tap when O1 was having a bath. That stuff, being in the world E, was H2O. In the corresponding learning situation, O2’s parents pointed to stuff that came out of the bath-tap on T E, which is XYZ.

This allows a referentialist response to incommensurabilism that is different from the Fregean one. The referentialist can say that what- ever else changes during a scientific revolution, the causal connections between the scientists (and their use of words) and the things in the world do not change. Their beliefs may change radically, but what those beliefs are about will not change, because that relation, the referential relation, is not fixed by beliefs but by a causal connection that remains in place. O1 may grow up to have all sorts of strange beliefs about water and these may change a great deal, but they are still all beliefs about water, the stuff that is H2O, because the causal connection between his use of the term ‘water’ and the stuff water (H2O) was established before Kuhn on Reference and Essence 51 and independently of those beliefs4. Because on the causal view of reference-fixing, reference is fixed inde- pendently of beliefs, the causal view does not fall prey to the objections to the Fregean view. For example, it doesn’t matter much if one wants to say that much or all of a theory is part of the ‘meaning’ of some scientific term, because any such conception of meaning cannot be one where meaning determines reference. And it is reference that is signifi- cant in being able to say that a later theory corrects an error in an earlier theory, or in saying that later scientists know more about some subject matter than did earlier scientists. As regards the realism debate, the idea of meaning becomes insignificant, as does the incommensurabilist thesis that there is meaning change of a kind that precludes translation5. It should be noted that a pure causal theory of reference (only the causal connection counts — theoretical beliefs play no part), is not the only account of reference consistent with the Kripke-Putnam rejection of Fregeanism. Mixed accounts will do also, and there are other accounts where a causal connection is not always required. It is intriguing to note that at one point Kuhn himself took a very similar view:

The distinction between a theoretical and a basic vocabulary will not do in its present form because many theoretical terms can be shown to attach to nature in the same way, whatever it may be, as basic terms. But I am in addition concerned to inquire how “direct attachment” may work, whether of a theoretical or basic vocabulary. In the process I attack the often implicit assumption that anyone who knows how to use a basic terms correctly has access, conscious or unconscious, to a set of criteria which define that term or provide necessary and sufficient conditions governing is application [Kuhn 1974, 467 footnote 11].

Here Kuhn seems to be rejecting a Fregean approach to reference and endorsing one that allows for a direct attachment to nature (i.e. not via a set of criteria or descriptions), of the kind that Kripke and Putnam promote. However, as we shall see, Kuhn later rejected and attacked the Kripke-Putnam approach. It is interesting to ask why Kuhn’s view changed. I speculate that Kuhn was not conscious of a change and that 4 What would be required for a change in the reference of O1’s term ‘water’ would not be a change in O1 beliefs, but a change in O1’s causal connections with kinds of stuff. So if O1 were moved, unknowingly, to TE or a TE-like place, his new causal contact with XYZ may mean that in due course O1 might be referring to XYZ with the term ‘water’ and no longer to H2O. 5For a discussion of the causal theory and its variants in relation to incommensu- rabilism see [Sankey 1994a] and [Bird 2000, 179-181]. 52 Alexander Bird the difference in view represents a difference in intended contrast, a dif- ference in date of writing, and a difference in emphasis of research. The passage quoted is a footnote to a 1974 paper on paradigms, which were the focus of his early work. One of the key elements in the paradigm idea is to oppose the view that scientific deliberation is a matter of employing rules. In extending this idea to the role of paradigms in conferring mean- ing on terms, it is natural to claim that meaning is not specified by rules (e.g. correspondence rules, criteria, necessary and sufficient conditions etc.) but instead may be conferred other means, for example, by direct attachment. Later, however, Kuhn’s focus turned much more towards incommensurability, and in this context the idea of direct attachment looks unwelcome since it would undermine incommensurability in the way described, and hence is appropriate for attack in the 1990 paper [Kuhn 1990a]. Earlier I mentioned that the Fregean account of referentialism does not guarantee continuity of reference. It is possible for the sense con- nected with a word to change sufficiently that its reference changes also. Nonetheless, the dialectical relevance of Fregean referentialism is that it shows how incommensurability and scientific realism can be consis- tent. Thus, as it stands, incommensurability does not threaten scientific realism, if the Fregean view is right. To show that it does, one would additionally need to show that the relevant shifts in sense were sufficient to yield shifts in reference also (but without involving reference failure). Similar remarks may be made with regard to the version of referentialism based on the causal theory of reference. There can be continuity of causal connection, and so continuity of reference, even though there are changes in the theory associated with a term. So again, while some version of the thesis of incommensurability (e.g. concerning the impossibility of trans- lation) might be true, it would still be consistent with scientific realism6. That is enough to remove the immediate threat posed by incommensu- rability. The causal theory of reference does not itself guarantee that there will always be continuity of reference. Even on this theory it is possible for the reference of a term to change. It has been said that the name ‘Madagacar’ was originally applied to the mainland of Africa by those who lived there, but European explorers misunderstood their in- terlocutors and applied it to the large island that now bears that name. The use of the name in connection with the island by those explorers and their successors forged a new causal connection between the name

6It might be mentioned, however, that the causal theory of reference, in making do without the notion of sense, casts some doubt upon there being a problem of translatability. Kuhn on Reference and Essence 53 and the island and it is this use we have inherited. Now, it is conceiv- able that something like this could happen in science. One could argues that Democritus’ ‘atom’ has a different extension from ours7. But plau- sible cases are few and far between. What is required is that there is an established causal link to one reference or extension and that a new causal link is forged to another reference or extension. Although Kuhn mentions ‘redubbing’ in the title of his paper, he nowhere argues that such shifts actually take place. To make out a case just the like the ‘Madagascar’ case, one would have to show that the later scientists mis- took the intentions of the earlier scientists. That is a possible scenario, but on the whole one might judge it to be unlikely. Elsewhere he does assert that there have been changes in extension. For example, he argues that the extension of ‘planet’ has changed, because before Copernicus the Sun was held to be a planet but the Earth was not, whereas now we take the opposite to be true. But this of course does not establish any shift of extension rather than a shift in what the extension was thought to be [Bird 2000, 160-162]. We are often wrong about extensions, and we often disagree about them. To conclude, the causal theory of reference does not itself guarantee continuity of reference. It is conceivable that revolutionary changes in science result in shifts of reference and extension of the ‘Madagascar’ variety. But it would take a lot more historical detail than Kuhn has offered to make out such a case. As it stand, the causal theory shows how there can be continuity of reference despite even revolutionary scientific changes, and so shows how scientific realism is not threatened by the thesis of incommensurability as Kuhn formulated it.

5 Criticising Putnam

The causal theory of reference and Putnam’s argument that gives rise to it have come in for considerable discussion and criticism. I shall consider here only criticisms related to our discussion of Kuhn. The critic might first remark that it is unlikely that O1 and O2 have analogous beliefs. After all (on E) it is widely known that water is H2O (and correspondingly it will be known on T E that water is XYZ). If O1 and O2 share in this widespread knowledge then they will have distinct beliefs, whereas the argument requires that they have isomorphic beliefs. The most straightforward reply is simply to stipulate that in the example

7Although one might doubt where the extension of Democritus’ use of the term is established by a causal connection, rather than via a sense. 54 Alexander Bird

O1 and O2 do not have this knowledge. Although they may know that substances are elements or compounds made up of elements in chemical combination, they may not have had enough education to know which compound water is. The objector might respond by suggesting that what, for O1, fixes H2O as the referent of water, is the belief, widespread in O1’s society on E, that water is H2O. This would still abandon the letter of Fregeanism, since it would be no state of O1 that fixes the reference of ‘water’. Nonetheless, it might be said to retain the spirit of Fregeanism, since the proposal is, in effect, that senses exist but are social rather than individual. A standard way of cutting through all of this discussion is to turn our attention to the ancestors A1 and A2 of O1 and O2 respectively, who inhabit E and T E in 1750. Since this date is before the discovery of the chemical constitution of water, the beliefs of A1 and A2 are isomorphic as are the beliefs of A1’s society and A2’s society. There is no reason to suppose that the reference of ‘water’ has changed between A1 and O1 — what we refer to as water is the same stuff as what our ancestors in the eighteenth century referred to as water. Similarly A2 and O2 are referring to the same stuff. Thus A1 is referring to H2O and A2 is referring to XYZ. And so once again we have a difference in reference without any difference in belief, and so without a difference in sense — whether individual or social. Kuhn’s primary response to Putnam is to point out that the existence of XYZ is chemically impossible — at least, it is incompatible with what modern chemistry tells us. Let us define ‘water-like’ thus. Something is ‘water-like’ if it has the superficially observable properties of water (it is a tasteless, colourless substances, boils at 100◦C, freezes at 0◦C, support life etc.) Thus according Putnam’s story, XYZ is water-like but is not water. Kuhn points out that unless modern chemistry is badly wrong, it is not possible for there to be a water-like substance that is not H2O. There can be no water-like XYZ, unless XYZ is H2O after all. So the envisaged scenario is impossible, as far as we know. But were it possible, then modern chemistry is wrong, and hence the discovery on T E that water is XYZ would prompt a scientific revolution. Consequently, even if O2 were untouched by this, the (scientific) society which surrounds him would be very different from that surrounding O1. I find it difficult to see what the relevance of Kuhn’s response is sup- posed to be. The causal theory and essentialism have both been placed under close and critical scrutiny by analytic philosophers. But Kuhn’s arguments have been ignored even by the most stringent critics of Kripke and Putnam. In my view this is because Kuhn seemed to have a tin ear for the sort of philosophical argument that is standard in modern phi- Kuhn on Reference and Essence 55 losophy (though less common in philosophy of science than elsewhere). Nonetheless, Read and Sharrock have sought to resurrect Kuhn’s ar- guments. They say “[Kuhn] is raising a fundamental difficulty for the essentialist/referentialist view. He is saying: ‘If we try taking Putnam’s example seriously it turns out that Putnam does not really offer up a tenable thought-experiment after all’.” [Read & Sharrok 2002b, 154]. Let us reflect on what Putnam’s example is supposed to be and do. Read and Sharrock call it a ‘thought-experiment’. If it is a thought- experiment, it is a thought-experiment not in chemistry but in the phi- losophy of language. It is intended to show us how particular words and expressions function. In particular it is designed to show what does and what does not fix the reference of our natural kind terms. It does this by getting us to reflect on a particular imaginary scenario, and eliciting our judgments about what the kind terms used by the imaginary people in that imaginary scenario refer to. The ‘data’ yielded by the thought- experiment are those judgments (that O1 refers to H2O while O2 refers to XYZ). Those judgments license the inference that our implicit un- derstanding of the function of kind terms is that they do not have their references fixed by a speaker’s beliefs. Since we are competent users of the English language we may be expected to have a reliable implicit un- derstanding of the function of various categories of expression in English and so we may infer that in fact kind terms do not have their references fixed by a speaker’s beliefs. Does Putnam’s imaginary scenario have to be a possible scenario for it to do its work? No it does not. Putnam is not telling us that XYZ is possible. He is asking us to imagine that it is possible. Remember that the relevant data are our judgments about what the imaginary O1 and O2 are referring to in the imaginary scenario. So for the thought-experiment to do its work it is necessary only that the scenario be imaginable. And here ‘imaginable’ need be taken only in a very weak sense. We want to elicit judgments from ourselves and others in response to the imaginary scenario, and for that we need only think that the scenario is possible. Even if in fact it is impossible, that is no obstacle to our imagining that it is possible or to entertaining the scenario. And there are certainly conceptions of ‘imagine’ that allow this. For it is perfectly coherent to imagine even mathematical impossibilities being possible. For one can, in the relevant sense, imagine its being possible to trisect any angle. Say one were doing a study concerning what mathematical propositions people find interesting or surprising. It is perfectly coherent to try to elicit a judgment from someone by asking, “Imagine that you could trisect any angle. Would you find that an interesting or surprising possibility?” 56 Alexander Bird

It is no objection to such a study that it is impossible to trisect the angle. Nor is it at all relevant that if it were possible to trisect the angle, then modern mathematics would be badly wrong and discovering that one could trisect the angle would lead to a revolution in mathematics.

6 Defending Putnam

Although the above is an entirely sufficient response to Kuhn’s comment, I also suggested that in order to bypass all such considerations we could imagine Putnam’s scenario being discussed in the early to mid nineteenth century [Bird 2000, 183]. The idea is this. The discovery that water is H2O was a development that emerged in the first half of the nineteenth century, with the most important steps being taken in the period be- tween 1804 and 1820, thanks initially to Dalton and then to Berzelius. However, at that time chemistry was in a sufficiently nascent state that it is plausible to suppose that Berzelius and his contemporaries could not be sure that there is no distinct compound that shares the superficial properties of water. We now have to imagine some forerunner of Putnam carrying out his thought experiment in 1850. We elicit the same judg- ments, that in using the term ‘water’ O1 on E is referring to H2O while O2 on T E is referring to XYZ, even though the beliefs they have are the same (remember that O1 and O2 do not know much chemistry). How- ever this time, it is not open to a putative forerunner of Kuhn’s to object that there could be no such XYZ that has the superficial properties of water but is a different compound. Read and Sharrock respond to this proposal as follows:

But this just seems incoherent: it seems that now there no longer is a thought-experiment. For how are we supposed to know that water is H2O if we cannot rule out that some water is XYZ, if we cannot rule out XYZ as a starter in the game? And we cannot rule out the latter unless (e.g.) we know that XYZ cannot have the surface properties of water (. . . ). Unless and until one has a good scientific reason for insisting water’s extension cannot include XYZ, one will not need to endorse Putnam’s ‘externalist’ conclusion. Kuhn’s point is: such good scientific reason is ‘only’ in fact given by the taxonomic etc. structure of modern chemistry 8.

This argument is not entirely clear. But it seems to be saying the fol- lowing:

8See [Read & Sharrock 2002, 154] (emphasis in original). Kuhn on Reference and Essence 57

(1) to know that water is H2O one must know that no XYZ can be water-like (i.e. no substance other than H2O can have the surface properties of water); and hence:

(2) on my assumption that in 1850 they did not know that there is no water-like XYZ, they did not know then that water is H2O; and so:

(3) because in 1850 they did not know that water is H2O they could not then have run Putnam’s thought experiment.

If this is a correct interpretation, then the Read and Sharrock argu- ment errs in three important respects: (i) it fails to understand Putnam’s argument; (ii) it seems to assume precisely what Putnam’s argument is intended to disprove; (iii) it contradicts what chemists and historians of chemistry themselves say. (i) Read and Sharrock seem to think that by moving the thought experiment to 1850 I have undermined Putnam’s thought-experiment. Whereas the experiment is possible in 1950 it is not possible in 1850. This is because in 1950 we knew there can be no water-like XYZ, which, ex hypothesi, we could not know in 1850. But this is wrong. It plays no part in Putnam’s though experiment that we know that there can be no water-like XYZ. On the contrary, Kuhn’s criticism is in part that Putnam failed to notice that accord- ing to modern chemistry there can be no water-like XYZ. The thought experiment works just as well in 1850, because those who run the exper- iment will be able to judge (or so Putnam and I expect) that individuals whose contact is with XYZ and not with H2O will be referring by ‘water’ to XYZ and not to H2O. (ii) Read and Sharrock assume in (1) above that knowing that water is H2O requires knowing that nothing other than H2O has the surface properties of water. Why do they think this? The only reason I can think of is that they take the surface properties of water to be definitive of what water is. Something is water if and only if it has the surface properties of water. From this it would indeed follow that water is H2O only if nothing other than H2O can have the surface properties of water. But the idea that something is water if and only if it has the surface properties of water is precisely the idea that Kripke and Putnam are trying to 58 Alexander Bird undermine. Remember that O1 and A1 know only about the surface properties of water (and correspondingly for O2 and A2, concerning what they call ‘water’). So if the reference of the term ‘water’ were fixed by their beliefs about water, then it would be fixed by beliefs about surface properties alone. But since, as the thought experiment aims to show, reference is not fixed by their beliefs, it follows that what water is cannot be defined solely in terms of its surface properties. So when Read and Sharrock assume in their criticism that water can be defined in terms of its surface properties alone, they assume what Putnam sets out to show is false. They beg the question against him. (iii) Let us look more closely yet at the assumption (1) that knowing that water is H2O requires knowing that nothing other than H2O has the surface properties of water. That means that either (a) Berzelius (who died in 1848) did not know that water is H2O, or (b) Berzelius did know that nothing other than H2O could have the surface properties of water. But neither of these propositions is true. Berzelius certainly thought he knew that water is H2O, and certainly historians of chemistry attribute that knowledge to him. But there is no reason to suppose that Berzelius ever gave serious thought to the question, could something other than H2O have the surface properties of water, and there is even less reason to suppose that he did or could have known such a thing. In the quoted passage, Read and Sharrock seem to be saying that to know that water is H2O, one must know that nothing other than H2O is water-like, and that this knowledge must be based on good scientific reason, of the kind that only modern chemistry provides. (I presume from the context that ‘modern’ means twentieth or twenty-first century). But again that is false. As I have said, coming to know that water is H2O, as Berzelius and his contemporaries did, did not require thinking about what other than H2O could be water-like.

How did chemists come to know that water is H2O? The important work in showing that water is a compound of hydrogen and oxygen was carried out by Lavoisier, although similar experiments were carried out at the same time by Cavendish, Priestley, and Monge. The experiments were of two kinds: those that synthesized water, and those that anal- ysed water by decomposition. In 1781 all the above-mentioned chemists found that the burning of ‘inflammable air’ (hydrogen) produced what they recognised as water. None seemed to ask whether water might be compounded of quite distinct substances. (Of course, water could be produced by other processes, such as the reaction of inflammable air with metallic calxes. But that just confirmed Lavoisier’s view that the calxes contained oxygen). However, they could have had no theoreti- Kuhn on Reference and Essence 59 cal reason for supposing that no other compound could produce a sub- stance indistinguishable from water. (One hundred years later one could argue the point thus: to be water-like a substance must either be com- posed of small molecules, with strong inter-molecular forces, or of large molecules. All small molecules are known, and the only water-like one is H2O. Larger ‘molecules’ are either crystals (including metals) or are organic compounds, all of which are not water-like. But such thoughts were not available to Lavoisier and his contemporaries). Quite probably there was an unstated background assumption that distinct compounds would have distinct observable properties, which implies that if the ox- ide of hydrogen is water-like, then nothing else would be. But such an assumption could hardly have been sufficiently well grounded to provide the ‘scientific good reason’ that Read requires for supposing that there is no other compound like water. Instead of relying exclusively on such an assumption, what clinches the identification of water as the oxide of hydrogen, is the dissociation of water by passing steam over heated iron. Lavoisier showed that if one passed steam through a red-hot gun barrel (and, in later experiments, over iron filings), the products were inflammable air and a calx of iron, just like iron ore. The analysis of water by decomposition removed any room for doubt that the substance produced by burning inflammable air is water (al- though the chemists seem to have shown little doubt on that score). At the same time, the decomposition experiments were not by them- selves conclusive for all (for example, Priestley hypothesized that the in- flammable air had been contained in the iron). Of course, the synthesis of water from hydrogen and oxygen and the decomposition of water into hydrogen and oxygen, are experimental results that are logically compat- ible with the view that the extension of ‘water’ includes everything that has water’s surface properties. Thus those results are compatible with a view which says that there could be kinds of water that are not com- pounds of hydrogen and oxygen. It is instructive that neither Lavoisier nor any of his contemporaries considered such a possibility. The fact that their samples of water were a compound of hydrogen and oxygen licensed the conclusion they drew: water is a compound of hydrogen and oxygen. What is behind this license is not that they had good, specific, scientific reasons for supposing that there is in fact no other substance that has water’s surface features — for as we have seen, there were no such reasons. Rather, those chemists all took it that their samples as well as similar sources (i.e. the wells, rivers, rain etc. from which they might have obtained, by distillation, other samples of water) were samples of a single substance. That substance is water. The fact that they had not 60 Alexander Bird ruled out the possibility of a water-like substance on Mars that is not a compound of hydrogen and oxygen was irrelevant, since that substance was not a potential source of a sample. They would have had no inter- action with that substance. A fortiori, the fact that they had not ruled the possibility of synthesizing some water-like substance that might or might not exist in nature was irrelevant too, since that substance too was not a potential source of samples for them. It is true that Lavoisier et al. might have been mistaken in supposing all their samples and po- tential sources of samples to all be samples of the same substance. But notice that the risk of their being mistaken in this assumption is much less than the risk of being mistaken in the assumption that there is no possible substance that is water-like other than their samples. To sum up: we may make two contrasting hypotheses about what Lavoisier et al. meant by ‘water’ (‘eau’ or ‘vatten’ etc.).

(i) The extension of ‘water’ is precisely whatever is water-like. (In which case, in concluding that water is a compound of hydrogen and oxygen, they were making the highly risky assumption that there exists no other possible compound that is water-like and that no such other compound could be synthesized). (ii) ‘Water’ refers to that single substance of which all actual water- samples and potential water-samples (i.e. rain, wells, rivers etc. from which Lavoisier et al. could have obtained samples) are in- stances. (In which case, in concluding that water is a compound of hydrogen and oxygen, they were making the much less risky assumption that their water-samples and potential water-samples were all instances of a single substance).

The second of these hypotheses makes a much better explanation of why Lavoisier, Dalton and so on, reasoned as they did. First, we know that they did make the assumption ascribed to them in (ii). Indeed it is an assumption common to all those interested in the chemistry of water going back to Aristotle and before. But there is no evidence that they made the assumption ascribed in (i). Secondly, if we take it that the chemists in question were rational men, it is more plausible to attribute less risky assumptions in their reasoning than more risky ones. Putnam’s thought experiment is one way in which we can see that the function of kind terms is to name a single kind, one with which we are interacting. But it is not the only way. The way in which people reason in actual circumstances is another source of argument. This is be- cause people’s reasoning indicates their commitments and assumptions. Kuhn on Reference and Essence 61

And since use of a term involves certain assumptions and commitments (e.g. concerning the extension of that term), reasoning using that term can reveal which assumptions an individual is making, and hence can reveal the function of a term. The reasoning of late eighteenth and early nineteenth century chemists reveals a commitment to a Kripke-Putnam view of natural kinds rather than a Kuhnian or Fregean one.

7 Essentialism

Earlier I separated referentialism from essentialism. The referentialism of Putnam is however related to essentialism. Fregean referentialism held that a term would pick out its referent by virtue of that referent satisfying the sense of the term. Putnamian referentialism holds that certain terms, including natural kind terms name their referents. This is an important difference. For consider the propositions: ‘George Orwell wrote political novels’ and ‘George Orwell is Eric Blair’. Clearly the former might not have been true had circumstances turned out differently. But the latter cannot but be true, however things might have been. Since ‘George Orwell’ and ‘Eric Blair’ are names of one and the same man, the sentence ‘George Orwell is Eric Blair’ simply says of a certain man that he is identical to himself. Since nothing can fail to be itself, under any possible circumstances, it is necessarily the case the George Orwell is Eric Blair. The Putnamian view does not deny that the Fregean way of refer- ring might be true for some terms — it just denies that it is true for all terms (specifically, it isn’t true for natural kind terms and proper names). Something like the Fregean view might be right for expressions such as ‘my favourite colour’, ‘the nearest planet to Earth’ etc.9 Such terms might have picked out different objects had matters been other- wise, and indeed they may pick out different objects at different times. The difference between terms that pick out the same objects under all possible circumstances and those that may pick out different objects, is marked by saying that the former are ‘rigid designators’. It is not only names of people and natural kinds that are rigid designators. Let us as- sume for illustration that a person could not have had different parents from the parents he or she does in fact have. Therefore, since ‘Auberon Waugh’ designates the same person under all possible circumstances, so does ‘the father of Auberon Waugh’, and the latter is a rigid designator also. Now consider ‘The father of Auberon Waugh is Evelyn Waugh’. Since this is true the terms ‘the father of Auberon Waugh’ and ‘Evelyn

9Russell, however, went on to deny that properly speaking these are referring expressions at all. Instead they are disguised forms of quantification. 62 Alexander Bird

Waugh’ pick out the same man. Since those terms are rigid designators, they each pick out the same man in all possible circumstances. And so ‘the father of Auberon Waugh’ and ‘Evelyn Waugh’ pick out the same man in all possible circumstances. Hence ‘The father of Auberon Waugh is Evelyn Waugh’ is necessarily true. Looking at this another way, just as in the case of ‘George Orwell is Eric Blair’, the proposition says of a particular man that he is identical to himself, which of course cannot be anything but true. The lesson of all this for natural kinds is as follows. We have already seen that ‘water’ functions like a name and so is a rigid designator. The same may be said, for the same reasons, of ‘hydrogen’ and ‘oxygen’ and of the chemical symbols ‘H’ and ‘O’. The chemical expression ‘H2O’ is clearly not a name in the ordinary sense. But like ‘the father of Auberon Waugh’ ‘H2O’ is a rigid designator, since there is just one substance that can be a compound of hydrogen and oxygen in the ratio 2:1. Since it is true that water is H2O, then ‘water’ and ‘H2O’ designate the same substance, and since those terms are rigid designators, they designate the same substance under all circumstances. Hence ‘water is H2O’ is a necessary truth. Note that in reaching this conclusion all that was assumed was (i) that water is H2O and (ii) that ‘water’ and ‘H2O’ are rigid designators, being names or functioning like names. That it is necessary that water is H2O lends support to the view that water has an essence, namely that it is H2O. Locke tells us that the essence of something is some property such that something could not be that thing without possessing that property. And because necessarily water is H2O, it is indeed the case that something could not be water without being H2O. The same conclusion can be reached in a slightly different way from Putnam’s arguments. Those show that natural kind terms such as ‘wa- ter’ function as names, picking out a natural kind. So the extension of the predicate ‘is water’ includes all and only samples of that kind. What makes something a sample of a particular kind? There is room for some debate on this, but one thing is sure, and that is that members of the same kind must bear some deeper similarity than mere superficial resemblance. A robot cat would not be of the same kind as animal cats, however convincingly it behaved as a cat, since a creature with copper and silicon on the inside constructed by engineers does not belong to the same kind as an animal of flesh and bones begat in the standard way by its parents. The clearest cases of entities all belonging to the same kind come from physics, since all electrons are exactly alike and all protons are Kuhn on Reference and Essence 63 exactly alike and so on. So the kinds ‘electron’ and ‘proton’ are perfectly homogeneous. Moving on to chemistry we find that the kind terms have inhomogeneous extensions. This is because atoms and molecules might be in different states of excitation, and because of the existence of isotopes. Thus not all H2O molecules are identical. Nonetheless they all belong to the same chemical kind. It is plausible to suppose that ‘sameness of kind’ may be fixed contextually. Thus what is meant by ‘same kind’ by chemists is fixed by their interests as chemists. Their interests do not extend to the differences between isotopes since these make no qualitative difference to chemical reactions. Thus to answer the question posed by Kuhn, ‘is heavy water really water?’ is ‘yes it is’ [Kuhn 1990a, 312]10. There are other ways in which samples of what we ordinarily call water are not all the same. Much of what we call water contains consid- erable quantities of what is not H2O. Seawater, dishwater, rain, mineral water and so forth all contain differing amounts of impurities. For this reason I stated the essentialist conclusion thus: ‘in all possible worlds water consists (largely) of H2O’. Read and Sharrock pick up on my use of ‘largely’ here. They ask whether essentialism would look so attrac- tive if the impurities included XYZ, in significant proportions (say 25%) [Read & Sharrock 2002, 156]. They are right to raise this point. The primary response must be to refer to my proposal that the sameness of kind relation is contextual. In the chemical context, the impurities found in seawater, rain etc. would not be permitted and to the extent that something contains anything other than H2O it is not a perfect sample of water. So if we are thinking of the chemical term ‘water’ then I was mistaken in including the parenthetical ‘largely’. Chemical water is in all possible worlds only H2O. On the other hand the exten- sion of our everyday term ‘water’ does include these impure samples. We should conclude that the term ‘water’ as used by the chemist is a different term from the same word ‘water’ as used in everyday English. Interestingly, the extension of everyday ‘water’ does not cover samples that may have just as high a proportion of H2O (tea, a tomato etc.). So we cannot say that everyday water is just impure chemical water. It seems that the extension of the everyday term is governed by a variety of practical considerations that may not be characterised straightforwardly. (Nonetheless, all these observations are consistent with the hypothesis that the practical considerations have the effect of modifying a core con-

10Kuhn also asks the corresponding question, ‘is deuterium hydrogen?’. Again the answer is ‘yes’. Physicists distinguish protium, deuterium, and tritium as the three isotopes of hydrogen. 64 Alexander Bird ception of water, that it is a single chemical substance. Those complex, practical considerations would allow in samples with varying degrees of impurity but not all. If so, it would remain the case that necessarily everyday water is largely H2O. That said, since we are concerned with the chemists’ water, this is not strictly relevant). What if our samples of water had always had a large admixture of XYZ? This would be significant, since, ex hypothesi, the XYZ would contribute to the dominant superficial character of all the samples of water, in a way that impurities do not. If our samples contained small amounts of XYZ, then that too might be considered as a case of an impurity. But a significant quantity of XYZ could not be so dismissed. In such a case, if it is discovered that water samples contained not only H2O but also XYZ, then we would have to admit that pure water is not a single chemical kind but is a mixture of two compounds. And it would certainly be plausible to argue that water has no real essence (although some might reasonably argue that it is essentially a mixture of H2O and XYZ). But the fact that the referent of ‘water’ might not have a real essence in the hypothetical case where our samples are a mixture of H2O and XYZ does not show that in the actual case, where our samples are not such a mixture, that water is not essentially H2O.

Cases such as the hypothetical mixture of H2O and XYZ have been discussed before. The classic case is that of jade, which comes in two unrelated forms, jadeite and nephrite which are nonetheless superficially similar (though not entirely similar). In this case it is clear that there is no geological kind ‘jade’; what we call jade is a mixture of kinds. But that does not mean that diamond, which does not have samples that are of different constitutions, is not essentially a form of carbon. The point can be seen most easily with respect to persons and the proper names referring to them (where Kuhn is willing to admit a causal theory and its consequences). Consider the following scenario: what one has taken to be an individual named John is not that but is a pair of identical twins who frequently substitute for one another. It may not be entirely clear what the name ‘John’ does: does it refer to some disjunctive entity or to the mereological sum of the individuals, or does it not refer at all and are sentences using the name ‘John’ without a truth-value? But what is clear is that the possibility of such a case does not impugn the causal theory of reference and the necessity of ‘Eric Blair is George Orwell’. Similarly the case of jade and the hypothetical case of a mixture of H2O and XYZ does not give us any reason to doubt the application of the causal theory to natural kinds and the necessity of ‘all water consists of H2O’. Kuhn on Reference and Essence 65 8 Non-liquid water?

Kuhn also objects to Putnam’s identification of water and H2O on the ground that H2O includes ice and steam whereas in 1750 ‘water’ picked out only liquid water. Kuhn continues thus: “In 1750 the primary dif- ferences between the species recognized by chemists were still more or less those between what are now called the states of aggregation. Water, in particular, was an elementary body of which liquidity was an essen- tial property.” [Kuhn 1990, 311]. He goes on to say that the Chemical Revolution in the 1780s is what gave us a taxonomic transformation that allows a chemical species to exist in all three states. Read and Sharrock amplify Kuhn’s comments, remarking, “It is only given our post-Lavoisieric framework that we are forced to see water as largely H2O. Absent that framework, ‘water’-in-all-its-states is not necessarily a natural kind.” [Read & Sharrock 2002, 156]. These comments have very little impact on the essentialist argument for three reasons. Firstly, they are historically inaccurate. Phase transi- tions (changes of state) were widely regarded as changes in one and the same species long before Lavoisier. Secondly, the fact some chemists re- garded water, ice, and steam as different chemical species does not show that the extension of their term ‘water’ has failed to include ice and steam. Thirdly, even if ‘water’ as used in 1750 did not include steam, essentialist conclusions may still be drawn. Firstly, did scientists universally regard steam and water and differ- ent species before Lavoisier? The matter is far from as clear as Kuhn, Read, and Sharrock suggest. Aristotle tells us: “Now the sun, moving as it does, sets up processes of change and becoming and decay, and by its agency the finest and sweetest water is every day carried up and is dissolved into vapor and rises to the upper region, where it is condensed again by the cold and so returns to the earth.” He also tells us that ice, snow, hail, are hoar-frost are water solidified by cold, that water freezes in winter, and that ice is made up of water11. Locke starts by appearing to confirm Kuhn’s view “If I should ask anyone whether ice and water were two distinct species of things, I doubt not but I should be answered in the affirmative; and it cannot be denied but that he that says they are two distinct species is in the right.” [Locke 1690, III, vi, sect. 13]. But then he goes on to argue that someone brought up in Jamaica who found that in England a bowl of water froze over might regard the ice as hardened water and that “it would not be to him a new species, no more than congealed jelly, when it is cold, is a distinct

11See [Aristotle Meteorologica, 354b27-30, 388b14, 347b36, 385b5]. 66 Alexander Bird species from the same jelly fluid and warm; or than liquid gold in the furnace is a distinct species from hard gold in the hands of a workman.” Locke draws a quasi-Fregean lesson, that the extensions of our species terms are fixed by nominal essences. Remember that for Locke the real essences that would distinguish between whatever real species there are, are undiscoverable. He need not have drawn such a conclusion; he could have held that whether water and ice really are the same or distinct species depends on scientific facts unavailable to him and to his con- temporaries12. What is important is that Locke does not regard it as absurd or demonstrably false to think that ice and water and the same species, and furthermore that he regards it as given that phase tran- sitions for other substances (e.g. gold and jelly) are species-preserving, and so for Locke (and presumably his audience) it cannot be, pace Kuhn, that in general “the primary difference between the species recognized by chemists were still more or less those between what are now called the states of aggregation.”. It is worth noting that the demonstration by Cavendish, Priestley and Lavoisier that water is a compound, by explod- ing hydrogen and oxygen together seems to assume that water-vapour and water are the same substance. For the product of combustion is water-vapour which must be condensed to give liquid water which was then subjected to confirming tests to show that it is water. If conden- sation changed the actual substance, one could not identify water (the liquid) with the compound of hydrogen and oxygen. (These statements must be qualified by pointing out that even Lavoisier did not think that strictly water and water-vapour are the same species, for water-vapour is water combined with caloric). What these remarks show is that before Lavoisier it was reasonable to hold that different phases did not always differentiate between substances (and that even after Lavoisier the matter was not fully settled until the end of the caloric theory). In which case ‘gaseous water’ could not simply be a contradiction in terms. Rather it was a synthetic question whether freezing and evaporation involved a change in species13. The fact that many chemists did regard such changes as changes in species is no objection to essentialism. Indeed, as Kripke shows, a large part of the motivation for the causal theory is that it permits false beliefs about the

12Note that Locke is working with an idiolect view of language — we each have our own personal languages that we coordinate publicly. Without that, one might wonder why the proper response to the Jamaican visitor would not be ‘you’ve misused the word ‘water’; part of its definition is that it is a liquid’ — if, of course, water does have only a nominal essence. 13For this point and much other useful information on the subject I am very grateful to Robin Hendry. Kuhn on Reference and Essence 67 referents of the terms one uses. In the much-used fictional example, Lois Lane believes that Clark Kent and Superman are different people. But that is consistent with their being the same individual and necessarily so. Similarly someone who recalls Eric Blair from their shared schooldays at Eton might not know that he is the same man as George Orwell, the now famous author of Down and Out in Paris and London, and indeed might naturally think there are different individuals, in which case his belief is a necessary falsehood. It is noteworthy that Kuhn accepts the causal and essentialist story when it comes to the use of property names. He is even willing to agree that it comes very close to working just as precisely for some kind terms, such as ‘gold’ [Kuhn 1990a, 309]. (It is worth asking whether Kuhn’s partial acceptance of the causal-essentialist story is compatible with the Wittgensteinian interpretation given by Read and Sharrock). To de- fend his incommensurability thesis, what is required is that the story break down for key terms across scientific revolutions, even if it holds for others. Since water is a point of focus in the Chemical Revolution, Kuhn wants to show that there isn’t continuity of reference of ‘water’ across that revolution, even though there may have been for ‘gold’ and other kind terms that did not play such a central role. However, given the partial acceptance of the causal-essentialist thesis, Kuhn needs to have an especially convincing reason as to why what holds in the case of names (and perhaps some kind terms) does not hold in the case of ‘water’. For in the case of names, we see that ‘N’ and ‘M’ might be rigid designators referring to the same individual (hence necessarily N=M), yet someone might believe that N and M are not identical. And the same response is available to his objection based on the widespread (but not universal) view, before 1750, that steam and ice are not water. For the essentialist may (and should) respond that those involved had a false belief: ‘steam’, ‘ice’, ‘water’ all refer to the same substance and always have done. Those like Locke who thought otherwise were mistaken and those like his fictional Jamaican who thought that ice is hardened water were correct. The former would have been just as mistaken as someone who, to borrow Locke’s example, thought that solid and liquid gold are different substances (which Locke acknowledges they are not). Kuhn has given no reason to reject this account of matters. As remarked above, the causal theory of reference does not guarantee continuity of reference. But it does make it more likely, even through revolutionary scientific changes. To make out a case for discontinuity of reference or extension Kuhn needed to give far more careful argument and detailed historical support than he did provide. 68 Alexander Bird

How damaging would it be were we to admit that ‘x is water’ did analytically entail ‘x is liquid’ in 1750? I have suggested that this would leave untouched the conclusion that all water1750 is H2O even though it would not be correct to say that all substances that are composed of H2O are water1750 (where water1750 is what was being referred to by ‘water’ when used in 1750) [Bird 2000, 183-184]. For we can form the expression ‘liquid water’ where our term ‘water’ covers all three phases. And thus if water1750 is necessarily liquid water and water is essentially H2O, then water1750 is also essentially H2O. Kuhn complains that if we are required to use descriptive terms in the specification of reference then we are back with the Fregean posi- tion that the causal theory was designed to avoid. But the cases are importantly different. For if we supplement the rigid designation with descriptive terms, the essentialist conclusions still follow. In Putnam’s arguments the problem was the insufficiency of a purely descriptive se- mantics for kind terms; his conclusions are thus consistent with a mixed causal-descriptive semantics (an approach which for many philosophers has supplanted the pure causal view while retaining its insights). What is important in all this is whether the incommensurabilist threat to realism survives. Kuhn has not given us a reason to suppose that it does. Indeed it is questionable whether the incommensurability thesis itself survives. I have suggested that Kuhn’s arguments against the view that our term ‘water’ is the same as or translates the mid- eighteenth century term ‘water’ (in the mouths of scientists) are very weak (even less does he show that the terms have different references). But note that in the course of his arguments that there is no such equiva- lence Kuhn supplies an alternative translation: ‘water’ (as used in 1750) is translated by ‘liquid water’ (as used by today’s scientists) and has the same reference as ‘liquid H2O’. He concedes that modern science is capable of picking out the stuff that people in 1750 labelled ‘water’ [Kuhn 1990a, 312]. If so, then the realists have what they want, a way of making clear that what scientists today say is in contradiction to some of what scientists in 1750 were saying. They thus are able to explain how, if today’s scientists are right, science has corrected and added to the science of yesteryear. Kuhn on Reference and Essence 69 9 Superficial properties are essential?

Kuhn regards the following argument as significant.

The so-called superficial properties are no less necessary than their apparent essential successors. To say that water is liquid H2O is to locate it within an elaborate lexical and theoretical system. Given that system, as one must be in order to use the label, one can in principle predict the superficial properties of water (just as one could of those of XYZ), compute its boiling and freezing points, the optical wavelengths that it will transmit, and so on. If water is liquid H2O, then these properties are necessary to it. If they were not realized in practice, that would be a reason to doubt that water really was H2O [Kuhn 1990, 312-313]. Again Kuhn overstates the scientific and historical case. The theoretical framework required to state that water is (liquid) H2O was in place by the time of Berzelius in the mid-nineteenth century. But that framework was not sufficient to permit Berzelius to make the calculations Kuhn refers to, even in principle. The theoretical framework required to be able to assert that water is (liquid) H2O is much thinner that Kuhn supposes. But Kuhn’s remarks are in any case once again irrelevant. The su- perficial properties would be necessary if the laws of nature contained within the relevant theories and used to compute the details of boiling point, freezing point, and so on, are themselves necessary. But if the laws are contingent, then it is much more difficult to show that the su- perficial properties are necessary. Most philosophers of science have held the laws of nature to be contingent and have taken it that the superficial properties are correspondingly also contingent. Now, it is possible for contingent laws to support necessary superficial properties. But the arguments are subtle and highly contentious, and have only recently been explored [Bird 2001], [Bird 2002]. Kuhn gives us no reason to think that with contingent laws the superficial properties will be anything but contingent too. Some philosophers do think that the laws of nature will be necessary. In which case, given the necessity of water=H2O the superficial properties will be necessary also. Again this view is contentious and Kuhn hasn’t said anything relevant to it. Finally, even if the superficial properties are necessary, as Kuhn maintains, that doesn’t show that they are essential. For as Kit Fine reminds us, the essence of an entity is much more restricted than the set of its necessary properties [Fine 1994]. We may thus distinguish between the essence of a substance and the non-essential but nonetheless necessary properties that follow from its essence. 70 Alexander Bird 10 Conclusion

We started by considering the apparent threat to scientific realism posed by Kuhn’s incommensurability thesis. The common response by the re- alist is to appeal to referentialism. Referentialism shows how incom- mensurability as a thesis about the mutual untranslatability of theories emanating from different paradigms is after all consistent with scientific realism. The referentialist response has been elaborated in particular in the form of the causal theory of reference. Related to the causal theory (but by no means identical to it) is the thesis of essentialism. Essentialism and the causal theory of reference have come in for con- siderable criticism, and the arguments are still live today. I have not discussed let alone deflected any of these criticisms here. In this paper I have considered only the criticisms brought to bear by Kuhn and elabo- rated by Read and Sharrock (which are very different from the criticisms usually discussed in the literature). Do their arguments provide some distinctive reason to doubt the causal theory of reference and essential- ism, and thereby undermine the referentialist defence of scientific realism against the threat posed by the incommensurability thesis? Did Kuhn spot something that other philosophers have missed? Despite the best efforts of Read and Sharrock to resurrect Kuhn’s criticisms, the fact is that Kuhn did not fully understand Putnam’s ar- gument and his criticisms are largely irrelevant. Those criticisms do not give the scientific realist a reason to doubt her views. Of course there are other reasons that have been advanced for doubting scientific realism and these have not been under consideration here. Furthermore, Kuhn’s own approach is itself an anti-realist one14. This creates difficulty in assessing Kuhn’s criticisms of referentialism. For in so far as referentialism is a component of scientific realism, a criticism that assumes an anti-realist viewpoint is question-begging. For that reason, I have not considered Kuhnian ways of adding to the points he makes, that together present an alternative, inherently anti-realist viewpoint. For example, Putnam’s arguments are framed in such a way that assumes that scientists can get to know the way things really are. While I do not think that the argu- ments need to be framed in an overtly realist manner, I have not here responded to criticisms of a Kuhnian sort that object to the realist way of framing the argument. For what we are considering here is the refer-

14Indeed, on some ways of understanding Kuhn’s incommensurability thesis, the ar- gument is from anti-realism to incommensurability rather than the other way around. For a discussion of the relationship between anti-realism and incommensurability see [Bird 2003]. 71 entialist defence of scientific realism against an alleged criticism. And it is clearly legitimate for the realist to frame her defensive arguments in realist terms. Given this dialectic, it needs to be repeated that the primary aim of the paper is limited to defending the referentialist version of realism against a particular set of criticisms, and not to defending realism against other kinds of criticism, let alone establishing the superiority of realism to its competitors. The primary aim is achieved so long as referential continuity remains an open possibility at the end of this paper. I have not sought to show that there definitely is referential continuity across revolutions in key cases. This would require more detailed historical work than I can present here, although I do suggest that the historical details presented in the case of ‘water’ point in this direction. That additional work would be required to show the superiority of the realist viewpoint, and that, as I have said, is not my current aim. The latter is limited to showing how referentialism can support realism and defending the causal version of referentialism against Kuhn’s specific criticisms. The conclusion I reach is that the realist can mount a fully adequate defence. 72 Semantic Incommensurability and Empirical Comparability: The Case of Lorentz and Einstein

Martin Carrier University of Bielefeld

Résumé : L’incommensurabilité sémantique est comprise comme la non- traduisibilité de concepts appartenant à différentes théories. L’objectif de l’ar- ticle est de proposer une reconstruction rationnelle de la notion d’incommen- surabilité qui sous-tend les écrits de Feyerabend et du dernier Kuhn. L’incom- mensurabilité, prétend-on, peut être reconstruite sur cette base en tant que notion cohérente, et des exemples pertinents peuvent en être donnés. L’impos- sibilité de la traduction entre concepts incommensurables provient de l’impos- sibilité de satisfaire conjointement deux conditions d’adéquation que la théorie contextuelle de la signification impose aux traductions. Les analogues concep- tuels potentiels s’avèrent, soit ne pas préserver les conditions d’application, soit ne pas reproduire les relations inférentielles pertinentes. L’incommensurabilité est ainsi construite comme le résultat d’un type particulier de relations concep- tuelles produit par l’incompatibilité des théories correspondantes. Ces relations conceptuelles sont suffisamment étroites pour rendre possible une comparaison empirique des assertions théoriques pertinentes. L’article s’efforce de rendre ces thèses plausibles en développant des exemples tirés de l’électrodynamique classique et de la relativité spéciale. Abstract: Semantic incommensurability is understood as non-translatability of concepts taken from different theories. My aim is to give a rational re- construction of the notion of incommensurability underlying the writings of

Philosophia Scientiæ, 8 (1), 2004, 73–94. 74 Martin Carrier

Feyerabend and the later Kuhn. I claim that incommensurability can be re- constructed on this basis as a coherent conception and that relevant instances can be identified. The translation failure between incommensurable concepts arises from the impossibility to jointly fulfil two conditions of adequacy that the context theory of meaning places on translations. Potential conceptual analogues either fail to preserve the conditions of application or to reproduce the relevant inferential relations. Incommensurability is thus construed as the result of a particular type of conceptual relations which is produced by the incompatibility of the pertinent theories. These conceptual relations are sufficiently tight to make an empirical comparison of the relevant theoreti- cal assertions possible. I try to make these claims plausible by elaborating examples from classical electrodynamics and special relativity.

1. Introduction

Incommensurability is among the catchwords of later 20th century phi- losophy of science. The notion of incommensurability in the non-geo- metrical sense relevant here was simultaneously introduced by Thomas S. Kuhn and Paul K. Feyerabend in 1962 [Kuhn 1962, 103], [Feyer- abend 1962, 58]. Kuhn conceived of incommensurability as arising from a deep-reaching conflict between paradigms or comprehensive theoretical traditions, a conflict supposedly transcending mere incompatibility. The adoption of a new paradigm entails the restructuring, as it were, of the relevant universe of discourse; the adherents of the two paradigms tend to talk past one another. In particular, incommensurability is intended to express that, first, disparate concepts are employed in each of the the- ories at hand, second, distinct problems are tackled, third, the suggested problem solutions are evaluated according to different standards, and, finally, perceptions are structured differently [Kuhn 1962, 103-110, 148- 150]. Feyerabend, by contrast, focused on the “inexplicability”, that is, the non-translatability of a term taken from one theory into the concep- tual framework of another one incompatible with the first [Feyerabend 1962, 52-62]. While the initial use of the term “incommensurability” varied signifi- cantly, it came to be restricted, subsequently, to two features. “Method- ological incommensurability” was intended to express the claimed inde- terminacy of judgment as to the comparative merits of different theo- retical approaches. “Semantic incommensurability” was supposed to de- note the non-translatability of statements from incompatible, strongly Semantic Incommensurability and Empirical Comparability 75 contrasting theories. In the following, I exclusively address this second notion of semantic incommensurability. This notion agrees with the one entertained by Feyerabend and the later Kuhn. My aim is to give a systematic reconstruction of the nature and impact of semantic incom- mensurability. Underlying the conception of incommensurability is the theoretical context account of meaning which both authors adopted for explaining the meaning of scientific terms in general. I try to show, first, that in- commensurability can be reconstructed coherently on the basis of the context account. I present incommensurability as a consequence of this semantic theory along with the historical observation that substantial theoretical revisions occur indeed. My conclusion is that incommensu- rability qualifies as a sensible notion. Second, I defend the coherence of the notion of incommensurability by offering relevant examples. My chief case concerns the non-translatability of concepts of Lorentzian elec- trodynamics and Einsteinian special relativity theory. This presentation is intended to buttress the claim that incommensurability is real and in- stantiated. Third, I explore the impact of incommensurability on empir- ical comparability. Incommensurability was perceived as a major threat to the possibility of rational theory evaluation. My aim is to dispel such worries. Incommensurable theories allow empirical comparison. The argument proceeds on the basis of the semantic principles adopted by Kuhn and Feyerabend. That is, given their own linguistic approach, in- commensurability does not result in a breakdown of comparing empirical achievements of the theories in question. Empirical comparison does not require translation and remains largely unaffected by incommensurabil- ity.

2. Meaning, Theoretical Context, and Adequate Trans- lation

Kuhn and Feyerabend accept the context theory of meaning. According to this account, the meaning of a concept is determined by its relations to other concepts and the meaning of a statement results from its inte- gration in a network of other statements. Another way of putting this is to say that the use of a concept determines its meaning. What a concept means is represented by the way in which it is applied to dif- ferent situations. The use of scientific concepts is specified by the laws of nature in which these concepts figure. The meaning of a concept like “electric field” is given by its lawful connections to related concepts such as electric current, charge or magnetic field. The concept “electric field” 76 Martin Carrier is understood if it is known, for instance, that such fields are produced by electric currents or variable magnetic fields and generate changes in the motion of charges, and so forth. Laws and theories supply a concept with a network of relations to other concepts, and this network determines to which situations the concept is properly applied. Such generalizations add to the meaning of the relevant concepts1. Translation in the sense relevant here concerns concepts of different theories. Translation requires the coordination of a linguistic item with another one taken from a different theoretical framework but possessing the same meaning. The understanding underlying the entire discussion of the incommensurability thesis is that translation needs to be precise (clumsy paraphrases don’t suffice) and provide a one-to-one correlation between expressions. The latter condition does not demand that one word is assigned to exactly one word; rather, coordinating strings of words with one another is quite legitimate. The issue is not about words but about semantic resources. It is not about terminology but about what can be expressed within a conceptual framework [Sankey 1994, 76-77]. On the basis of the context theory, the requirement of meaning preser- vation is to be interpreted as unchanged use. This notion of use compre- hends two features which should both be retained in translation. First, theoretical integration should coincide for the two items at issue. This applies, in particular, to the reproduction of standing inferential rela- tions among predicates or the statements formed by them. After all, it is such relations that provide the context relevant to the ascription of meaning. For example, the sentence “the tree over there is losing its foliage” implies: “there is a deciduous tree”. Analogously, “Wilfried is a bachelor” entails “Wilfried is not divorced”. The network of such rela- tions supplies predicates with their content; consequently, these relations should be preserved among supposedly synonymous expressions. Second, the conditions of application of concepts should remain unaltered. One of the reasons why the French predicate “x roule en deux chevaux” is disqualified as a translation of “x loves cats” is that their conditions of application exhibit hardly any correlation. The two predicates are only accidentally applied to the same objects; they differ in meaning for this reason. Synonymous concepts should refer to the same states of affairs. On the whole, then, the theoretical context account recognizes two chief determinants of the meaning of concepts. First, the inferential inte-

1[Kuhn 1983a, 576-577], [Kuhn 1987, 8], [Kuhn 1989, 12, 15-20]; see also [Irzik & Grünberg 1995, 297-298], [Feyerabend 1962, 76-81], [Feyerabend 1965c, 180]; see also [Papineau 1979, 36-45], [Sankey 1994a, 6-10]. Semantic Incommensurability and Empirical Comparability 77 gration of a concept which is specified by its relations to other concepts. The integration of scientific concepts, in particular, is provided, among other things, by the relevant laws or theories. Second, the conditions of application which are determined by the set of situations to which a concept is thought to apply (or not to apply, respectively). To these two sources of meaning correspond two constraints on adequate translations. Rendering a concept appropriately demands, first, the preservation of the relevant inferential relations, and, second, the retention of the con- ditions of application [Carrier 2001, section 4]. One of Kuhn’s most prominent historical claims is that science pro- ceeds at least sometimes through stages of significant and deep-reaching conceptual and theoretical alteration. There is drastic theoretical change in science. This view finds its most prominent expression in Kuhn’s characterization of scientific revolutions. Kuhnian revolutions are con- ceived as non-cumulative transitions. They do not involve the sustained elaboration of an accepted conceptual framework. On the contrary, a scientific revolution à la Kuhn consists in the revocation of fundamental principles of a discipline and their replacement by disparate ones. Fur- thermore, the disparity between pre- and post-revolutionary principles prohibits any smooth integration of the former into the framework of the latter. As a result of the far-reaching divergence between them, the pre-revolutionary theory cannot be reconstructed as the limiting case of the post-revolutionary one [Kuhn 1962, Chapters VIII-X]. Kuhn initially located the chief origin of theoretical disagreement in revolutionary periods in perceptual, methodological, and ontological changes, but later distinguished linguistic deviation as the crucial fea- ture of scientific revolutions. Incommensurability or non-translatability is shifted to center stage [Kuhn 1983, 684], [Kuhn 1987, 19-20]. A the- ory is thought to comprise a series of terms that are supposed to denote natural kinds. Such kind-terms indicate what is assumed to be of the same kind within the theoretical framework. Kind-terms represent ac- cepted similarity relations among objects or processes. Incommensura- bility is said to arise from the non-translatability of kind-terms which is attributed, in turn, to divergent judgments about similarity relations [Kuhn 1993, 315-318; 328; 336], [Irzik & Grünberg 1998, 211-212]. I wish to address Kuhnian relations of sameness in kind indirectly by examining first the relations among seemingly analogous concepts from theories separated by a scientific revolution and by exploring the options for giving adequate translations. Kuhn recognizes that the kind-terms of a theory are connected to the laws of this theory [Kuhn 1987, 20], [Kuhn 1993, 316-317]. I will deal with conceptual relations first and come 78 Martin Carrier back to sameness in kind later. An often quoted instance of a Kuhnian revolution is the Einsteinian Revolution, a part of which involved the substitution of Hendrik Lorentz’s classical electrodynamics by Albert Einstein’s special relativity theory. This is a revolutionary change by any measure so that the emergence of incommensurable concepts can be expected — provided that incommensurability is instantiated at all. I begin by giving a brief sketch of the relevant theories.

3. Shifting Theoretical Ground: The Example of the Einsteinian Revolution

One of the characteristics of Lorentz’s electrodynamic theory was the assumption of an immovable ether. The ether was held to be at absolute rest; it is not displaced through the motion of charged bodies. But such motions produce changes in the state of the ether, and these changes propagate through the ether with the velocity of light. The ether medi- ates in this way the interaction between charged objects. True motion is motion with respect to the ether. The equations of electrodynamics were restricted to frames at rest in the ether; they were thought not to hold for moving systems without adaptation. For instance, the velocity of light, as it features in Maxwell’s equations, was construed as its velocity relative to the ether. The measured value of this velocity should depend on the motion of the observer. However, no such dependence was found empirically. After Michelson and Morley had shown with high numerical precision in 1887 that no effect of the Earth’s motion on the velocity of light was detectable, Lorentz (following Fitzgerald) introduced his con- traction hypothesis. The length of a moved body in the direction of motion shrinks to such a degree that the change in the velocity of light induced by the motion is precisely compensated — as the Michelson- Morley null result demands. This length reduction is produced by the interaction between moved matter and the ether. The resting ether com- presses the body in passage through it, and this contraction precisely compensates the effect of the motion on the measurement of electromag- netic quantities. As a result of this double influence, no effect of the motion on the moved body will be registered2. Lorentz succeeded in deriving the contraction hypothesis from the principles of his theory by drawing on the additional assumption that the intermolecular forces that were supposed to hold a body together

2[Lorentz 1899, 268-270], [Drude 1900, 482], [McCormmach 1970, 47-48], [Nerses- sian 1986, 224], [Schaffner 1972, 113]; see [Carrier 2002, section 3]. Semantic Incommensurability and Empirical Comparability 79 and were thus responsible for the body’s dimensions transform like elec- tromagnetic forces. This assumption is made plausible by the notion that these intermolecular forces are similar in kind to electromagnetic forces or even of the same nature. Lorentz did not rule out the exis- tence of tangible effects of the motion of bodies through the ether. Only “many” electromagnetic phenomena were thought to appear in the same way irrespective of the observer’s state of motion [Schaffner 1974, 48]. In addition, Lorentz’s theory entailed that the frame of reference at rest in the ether was distinguished among the class of inertial frames in that it alone yields the true measures of lengths and velocities. The motion through the ether distorts spatiotemporal quantities. An optics textbook of the period put it this way:

Another way of explaining the negative results of Michelson’s experiment has been proposed by Lorentz and Fitzgerald. These men assume that the length of a solid body depends upon its absolute motion in space. [Drude 1900, 481].

On the other hand, the motion produces further effects that precisely offset the initial distortion — at least in “many” relevant phenomena. Lorentz’s account involves a sort of conspiracy among different factors brought forth by the motion of charged bodies. These factors are so contrived as to cancel each other out, concealing in this way the true motion of bodies from the unbefitting curiosity of human observers. While it is true that Einstein worked out his special theory of rela- tivity within the electrodynamic program and as a revision of Lorentz’s theory [McCormmach 1970, 74], [Darrigol 1996, 242-243], full-fledged special relativity is conceptually distinct from Lorentz’s account. There is historical continuity, to be sure, but the end-product of Einstein’s struggle with classical electrodynamics was markedly different from its Lorentzian ancestor. In spite of their common origin and their close his- torical ties, the conceptual resources invoked in both accounts exhibit semantic incommensurability. In contradistinction to Lorentzian electrodynamcis, Einstein’s rela- tivity theory proceeds from the so-called special principle of relativity which says that all inertial frames of reference are equivalent in every physical respect. As a part of classical mechanics, this principle had long been accepted. But the version suggested by Einstein was sup- posed to include electrodynamic processes; it implied that there is no privileged rest frame for electromagnetic phenomena. It follows that there are no absolute velocities; all velocities are relative to other bodies or frames of reference. The second axiom Einstein cites is the constancy 80 Martin Carrier of the velocity of light which says that the velocity of light is indepen- dent of the velocity of the light source. This constancy axiom follows from Maxwell’s theory; it is a theorem of pre-relativistic electrodynam- ics. The special principle and the constancy axiom together imply the invariance of the velocity of light according to which this velocity assumes the same value for all inertially moved observers. The special principle of relativity entails that the inertial motion of a system of charged bodies or of an observer has no impact on electromagnetic processes. That is, Einstein abolished both the distorting influence of the motion and the counteracting factor. According to special relativity, all inertial frames are equivalent right from the start; their equivalence does not require the action of a compensating mechanism.

Special relativity likewise entails a contraction of moved bodies. In fact, Einstein’s formula precisely agrees with Lorentz’s; both give the same ratio of length reduction for a moved body. But in spite of their mathematical identity, the Lorentzian and Einsteinian equations differ in meaning. Their semantic difference is rooted in the divergent under- standing of “velocity” in both sets of equations. For Lorentz it means “absolute velocity”, that is, velocity of the relevant body with respect to the ether rest frame. But for Einstein there is no such rest frame. The velocity in question is rather the relative velocity between body and observer.

This contrasting understanding has important ramifications. Con- sider a body and an observer moved at different speeds and assume that the observer registers a contraction of the body’s dimensions. It follows from Lorentzian electrodynamics that viewed from the angle of the moved and seemingly shortened body, the observer should appear expanded. After all, the moved body is compressed by the passage through the ether, and any length measurement using such shortened rods as standard should create the impression of expanded bodies. But on the basis of the principle of relativity, no states of absolute motion are admitted. Relative velocity is all that counts. Consequently, judged from Einstein’s perspective, the observer should appear contracted as well. All that can be said is that the two bodies are in relative motion so that they are both subject to length contraction. This means that Lorentz-contraction proper is asymmetric whereas Einstein-contraction is reciprocal. These considerations suggest the existence of significant conceptual discrepancies behind the superficial, specious identity of the formulas. I take a closer look at the relevant conceptual relations in the following section. Semantic Incommensurability and Empirical Comparability 81 4. Incommensurable Quantities in Classical Electro- dynamics and Special Relativity

The challenge is to give appropriate translations for Lorentzian concepts in terms of special relativity and vice versa. The spatiotemporal and dynamic measures in each theory constitute candidates for translation. Thus, the issue is whether counterparts for concepts like length, duration, velocity, and mass can be specified in the two theories at hand. I leave temporal quantities out of consideration. The reason is that Lorentz retained universal time but later learned from Einstein that it is his local time, rather than universal time, that the clock readings provide. Even after this recognition, however, Lorentz endeavored to stick to universal time and never reached a clear position in this matter. Unlike time dilation, Lorentz clearly endorsed length contraction and his pertinent formula agrees mathematically with Einstein’s. The issue, then, is translation. As I argued earlier, in light of the theoretical context account, a translation has to preserve the application conditions and the inferential relations of a term (see section 2). Let’s see how prima-facie translations fare in light of these requirements. The first attempt is to focus on conditions of application and to translate according to equality of measuring procedures: quantities that are determined empirically in the same way can be translated into one another. I won’t go into the details and simply state that length mea- surements based on rod transport or transmission time of light signals are equally accepted within both theories. That is, classical electrodynamics and special relativity roughly agree on the acceptability of length mea- surements. Measuring lengths by registering the round-trip travel time of a light signal, as it is done, for instance, in a Michelson-Morley setup is endorsed within the two accounts, and the results of the procedure are unanimously acknowledged as reliable. For Lorentz, the velocity of light would be altered by a possible motion of the observer, to be sure, but since the traversed spaces would change as well, the length ratios measured are trustworthy in any event. For Einstein, both the distor- tion and the counteraction are missing so that the procedure operates reliably anyway. However, the inferential relations fail to be retained. The crucial divergence concerns the interpretation of the relevant velocities. In Lorentz’s contraction formula the significant quantity is the velocity be- tween the moved body and the ether; in Einstein’s mathematically iden- tical equation the important magnitude is the velocity between the body and an observer. The disparate conceptual integration of the seemingly 82 Martin Carrier identical concepts of length and velocity becomes conspicuous once the relevant types of situation, as they emerge in the Lorentzian framework, are reconsidered in Einsteinian terms.

(1) Lorentzian situation: body and observer are equally at rest in the ether: no contraction. Einsteinian reconsideration: body and observer are at relative rest: no contraction. (2) Lorentzian situation: the body is in absolute motion, the observer is at rest in the ether: contraction of the body. Einsteinian reconsideration: body and observer are in relative mo- tion: reciprocal contraction. (3) Lorentzian situation: the observer is in absolute motion, body is at rest in the ether: contraction of the observer issuing in an apparent spatial dilation of the body. Einsteinian reconsideration: body and observer are in relative mo- tion: reciprocal contraction. (4) Lorentzian situation: both body and observer are in equal absolute motion: shrinkage of both body and observer but no net effect due to compensation (Michelson-Morley situation). Einsteinian reconsideration: body and observer at relative rest: no contraction.

The Lorentzian and Einsteinian approaches differ in judgment as to whether or not contraction occurs in a particular type of situation. Items (2) and (3) bring out the contrast between asymmetric Lorentz- contraction proper and reciprocal Einstein-contraction. If a moved body appears contracted to an observer, it is the observer which moves as viewed from the perspective of the seemingly shortened body. The rela- tivity principles entail that the observer appears contracted, he does not look stretched. This is different for Lorentz-contraction. Consider an observer moved with respect to the ether who measures the dimensions of a body at rest in the ether. In this situation, the observer’s exten- sion is reduced so that he will register an increased length of the body. The body appears enlarged, not contracted. Regarding item (4), when an observer is moved along with a body so that the two are at relative rest, Lorentz contraction occurs, to be sure, but remains hidden because of an equal contraction of the measuring rods. By contrast, Einstein contraction is entirely absent under such circumstances. Semantic Incommensurability and Empirical Comparability 83

Such differences in judgment indicate a change in the theoretical in- tegration of the concept of length. Consider a case of curvilinear (but approximately rectilinear) motion such as the annual revolution of the Earth around the Sun. In Lorentzian terms, the change in the direc- tion of motion entails that the body cannot be at rest in the ether all the time. This implies that contraction occurs. In special relativity, by contrast, this inferential tie is severed. The occurrence of a change of motion entails nothing as to contraction. All depends on the choice of the frame of reference. Conversely, whereas in special relativity the in- troduction of such a frame in a particular state of motion is sufficient for implying judgments as to the occurrence of contraction, no such unam- biguous consequences ensue from classical electrodynamics. In the latter framework absolute velocities are needed for making clear assessments possible so that the relativistic connection between relative motion and contraction is lost. I conclude that characteristic inferential relations for the concept of length are different in the two theories.

This first approach invoked sameness of measuring procedures as the basis for translation and involved the rule to retain as far as possible the conditions of application of the relevant terms. On this basis the electrodynamic concept of length appears roughly synonymous to the relativistic one. However, this translation rule fails to reproduce the relevant inferential relations. It falls short of underwriting adequate translations for this reason.

The second attempt is directed at the preservation of these inferen- tial relations. The pursuit of this line of thought amounts to explicating the terms “velocity” and “contraction” by delineating the role they play in classical electrodynamics or special relativity, respectively. Adopting the relativistic point of view, one could say that Lorentzian velocities are no relative velocities but refer to the motion of a body with respect to the ether, and one could add that these absolute velocities are allegedly responsible for length contraction phenomena. However, adopting such a translation rule drastically changes the conditions of application of the translated concepts. According to special relativity, there is no such thing as absolute velocity or as ether-caused contraction (let alone the converse spatial dilation). If the Lorentzian concepts of velocity and length reduction are simply grafted upon relativity theory, these con- cepts become empty. They are no longer legitimately applied to any phenomenon. The retention of the inferential relations is purchased at the expense of losing the conditions of application. This second approach also fails to provide an appropriate translation for this reason. 84 Martin Carrier

The relationship between electromagnetic and relativistic mass con- stitutes a second, analogous example. According to the so-called elec- tromagnetic mass concept, the inertial properties of bodies arise at least partially from the interaction between charges and fields. In this vein, Lorentz distinguishes between “real” and “total” mass. Real mass is of mechanical origin and invariantly characterizes a given body. Total mass is real mass together with a variable increase in the inertia of a charged body in motion as a result of its interaction with the ether [Miller 1981, 46-47]. Total mass governs the dynamic behavior of a body. Analogously, special relativity introduces rest mass and relativistic mass. Rest mass, like real mass, is an invariant characteristic of a body. Relativistic mass comprehends rest mass and a variable increase in inertia as a result of the relative motion of a body. Relativistic mass, like total mass, determines the dynamic behavior of a body. Further, the dependence of relativistic mass on rest mass and velocity is mathematically identical to the de- pendence of total mass on real mass and velocity. In addition, mass is evaluated in the same way in the two accounts in question. They both endorse determining mass values using a balance or collision processes (thereby drawing on momentum conservation). Therefore, the theoreti- cal integration of the Lorentzian and Einsteinian mass concepts coincide in some respect and the conditions of application agree, too. Accord- ingly, it appears that Lorentz’s “total mass” and Einstein’s “relativistic mass” are corresponding quantities, and that Lorentz’s “real mass” and Einstein’s “rest mass” are conceptually analogous as well. However, there are other features of the theoretical integration of these concepts of mass that differ considerably. Lorentz’s real mass is assumed to become manifest when the relevant body is at rest with re- spect to the ether. Einstein’s rest mass, by contrast, is obtained by an observer at rest relative to the body. Analogously, the value of total mass is supposed to be determined by the velocity of the body with respect to the ether, while the value of relativistic mass is assumed to depend on the difference between the velocities of body and observer. Consider a charged body which is moved through the ether at the same speed as an observer. The electrodynamic judgment is that the mass of the body departs from its real value. It does so for all observers, and conse- quently also for the observer moved with the body. In relativity theory, by contrast, relative motion is all that matters, so that an observer at relative rest measures the body’s rest mass. Electrodynamics draws on total mass for capturing this situation, special relativity takes rest mass to be the relevant quantity. Conversely, consider a body at rest in the ether as viewed from a moved observer. From the electrodynamic point Semantic Incommensurability and Empirical Comparability 85 of view, the dynamic behavior of the body is governed by its real mass whereas special relativity assumes that relativistic mass is the relevant magnitude. Underlying such differences in judgment is the divergent nomological integration of the mass concepts (which is veiled by the mathematical indistinguishability of the pertinent formulas). This divergence concerns the conception of the relevant velocities. Lorentzian electrodynamics takes the velocity between body and ether as the crucial parameter; Einsteinian special relativity assumes the velocity between body and ob- server to be of critical importance. As a result of this discrepancy in the nomological integration, the inferential relations between the mass concepts and other theoretical magnitudes disagree. For instance, the information that body and observer are in relative motion makes it im- possible to employ the concept of rest mass in order to account for the situation. Within a Lorentzian framework, nothing of this sort follows. In particular, it is not ruled out to invoke the supposedly analogous con- cept of real mass. Namely, the body might be at rest and the observer in motion. The Einsteinian inferential bond is missing in Lorentz. This consideration shows that these allegedly intertranslatable con- cepts are used differently. Actually, the semantic features can be ex- pressed in analogy to the above-mentioned relations among spatial quan- tities. The attempt to translate concepts from disparate theories leaves one with the choice between two equally unacceptable alternatives. The first one is to translate according to the relevant conditions of applica- tion. That is, the two terms are applied under the same circumstances. The catch is that the corresponding predicates do not exhibit the same inferential relations. In contradistinction to special relativity, classical electrodynamics does not license any relevant inference to be drawn from the fact that body and observer are in relative motion. The second op- tion is to translate such that the inferential relations are retained. This amounts to giving a description of ether-based electrodynamics. But the mass concepts specified in this framework are empty from a relativistic perspective: there is no motion relative to the ether. Thus, the condi- tions of application fail to be preserved. On the whole, then, the mass concepts in classical electrodynamics are incommensurable with the mass concepts in special relativity [Carrier 2002, section 4]. 86 Martin Carrier 5. Incommensurability, Split-Up of Natural Kinds and Shifts in Reference

Kuhn featured shifts in the assumed similarity relations as the primary characteristic of incommensurability. He claimed that the discrepancy between the taxonomies of natural kinds is the chief obstacle to trans- lation [Kuhn 1983a, 683], [Hoyningen-Huene 1989, 211-212]. Such kind- terms denote classes of entities that are judged to be of the same kind in light of a theory (see section 3). Incommensurable theories introduce par- tially overlapping classes of natural kinds. Such theories agree in judg- ments about the sameness in kind of some of the relevant entities, but disagree as to the sameness in kind of others. The shift toward a novel theory, incommensurable with the received one, produces a reshuffle of the classes of natural kinds. Such classes are torn into pieces, and the debris is reassembled to form novel, disparate classes. What is consid- ered as being of the same nature before a revolution may be regarded as different afterward. Conversely, what was thought to be different in kind may be taken as being alike in the new theory. It follows that two items which fall under the same category in one account are possibly to be expressed using different concepts in the other account. And two items labeled distinctly in one approach might be designated using the same concept in the other approach. Partial overlap or cross-classification of this sort vitiates translation and generates incommensurability [Kuhn 1990c, 4], [Irzik & Grünberg 1995, 299].

This cross-over of equivalence relations is manifest in the list of Ein- steinian reconsiderations of Lorentzian types of situations (see section 4). Ties of similarity are unraveled, and others are established in their stead. For instance, from a Lorentzian perspective, a body in absolute motion registered by an observer at rest in the ether (situation-type (2)) is of the same type as a situation in which both body and observer are in equal absolute motion (the Michelson-Morley situation (4)). The two situations are equally characterized by a contraction of the body— although it fails to become manifest if the observer is moved with the body. From Einstein’s point of view, by contrast, the two situations are distinct in kind in that relative motion, and consequently contrac- tion, is only present in the former, but not in the latter. Conversely, in Einstein’s framework all states of affairs that involve a relative mo- tion between body and observer are of the same type (situations (2) and (3)). By contrast, against the backdrop of Lorentz’s theory, it makes a difference whether the body or the observer is in motion.The observer Semantic Incommensurability and Empirical Comparability 87 will register a contraction if the body is moved but a dilatation if she is in motion herself. This consideration brings to the fore the Kuhnian partial overlap of kind-terms. In Lorentz, situation-type (4) is considered similar to situation-type (2), whereas in Einstein, situation-type (3) is taken to be so related to situation-type (2). The first natural kind is “being in absolute motion,” the second is “being in relative motion”. Both the Lorentzian and the Einsteinian kind-terms contain situation-type (2), but otherwise include different circumstances. This exemplifies that dis- parate systems of laws can tie different states of affairs together. Con- flicting theories tend to collect nomologically relevant properties into incompatible classes of natural kinds. The same reasoning applies to mass. In the Lorentzian framework, situations of the same type are characterized by equality of body velocity with regard to the ether — irrespective of the motion of the observer. Such Lorentzian kinds are dissolved in relativity theory through the in- troduction of the motion relative to an observer as the salient quantity. Conversely, Einstein forged other relations of natural kinds instead. Sit- uations of the same type are characterized by equal velocity with regard to an observer — irrespective of the motion relative to the ether. That is, what was formerly conceptually united crumbled into separate pieces. And what was considered distinct previously was integrated conceptu- ally. Incommensurable concepts emerge if, owing to nomological change, natural kinds are restructured. If a new system of laws is adopted that conflicts with a previous one, the former equivalence classes split up into heterogeneous components and realign to form new taxonomic struc- tures. This change of the class of properties to which a concept is rightly applied goes back to a change in the nomological integration of this con- cept. The use of electrodynamic and relativistic concepts is governed by contrasting sets of laws. It is this nomological contrast that constitutes the ultimate reason for the translation failure. The dissolution and the new formation of natural kinds which is placed at center stage by Kuhn is a proximate reason that follows from the divergence of the relevant inferential relations. 88 Martin Carrier 6. Empirical Comparison of Theories with Incommen- surable Concepts

Meaning discrepancy due to nomological divergence has a wider impact on the notion of scientific rationality. It affects the understanding of scientific progress and empirical comparison. Most linguistic theories accept the principle that meaning determines reference. Given this con- nection, a change in meaning suggests a shift in reference. Consequently, incommensurable concepts are likely to differ in reference. Barring the occurrence of coextensional terms like “rational animal” and “featherless biped”, theory change goes along with reference change so that the suc- cessor theory says different things about different objects — rather than different things about the same objects. This feature would certainly undermine a cumulative view of scientific progress. Progress could not be regarded as involving a better understanding of the same entities. Incommensurability appears to threaten, in addition, the comparabil- ity of the empirical achievements of rivaling theories. Without a common referential ground, no overlap among the empirical findings and prob- lems can be identified — or so it seems. Incommensurability appears to rule out any agreement as to which problems are to be tackled and which facts are relevant. Actually, it is not even clear whether the theories at hand are competing with one another. A competition requires same- ness of reference; competing theories entail divergent predictions about the same entities. But in the case of incommensurable theories, as the argument runs, sameness of reference can never be ascertained. The line of reasoning leading from translation failure to the exclu- sion of empirical comparison roughly runs as follows. Non-translatability implies that the content of one theory cannot be expressed within the conceptual framework of the other. But if it remains obscure what the allegedly rival theory says, there is no way to judge if it agrees or conflicts with the theoretical assumptions under scrutiny. If comparison of con- tent is ruled out, no comparison of the pertinent empirical consequences can be accomplished. In fact, however, empirical comparison remains a live option. Incom- mensurable theories need to be comparable in some respect in order to generate a non-trivial translation problem in the first place. A host of theories is not translatable into one another without anything significant coming out of it. Lorentzian electrodynamics cannot be expressed us- ing concepts from Darwin’s theory of natural selection, special relativity cannot be translated into game theoretical vocabulary. This is a rather unexciting feature. In order for non-translatability to become a non- Semantic Incommensurability and Empirical Comparability 89 trivial issue at all, such cases need to be excluded. The obvious way to do this is to draw on one of the defining features of incommensurability, namely, incompatibility of the laws involved. Incommensurable concepts are untranslatable since the relevant laws, as specified within each of the theories at hand, contradict one another (see section 1). But no such in- compatibility occurs in anyone of the just-mentioned cases [Feyerabend 1972, 304], [Hoyningen-Huene 1989, 213]3. But a conflict between two theories only emerges if there is some shared realm which they jointly address. The non-triviality of incom- mensurability requires that there is some range of phenomena that can be considered relevant for both theories. This common ground is suffi- cient for making empirical comparison possible. Consider a particular experiment for which both theories claim responsibility. Each of them captures the outcome by using its own observational vocabulary. As- sume that the outcome is such that it is justified, on the basis of one account, to conclude that a certain process, as specified in terms of this account, has actually taken place, while it is illicit, on the basis of the rivaling theory, to judge that the process required by this theory has occurred. The experiment and its result are described within the con- ceptual frameworks of each of the theories involved. The series of experiments Walter Kaufmann conducted between 1901 and 1905 constitutes an example. Kaufmann’s experiments were in- tended to measure the dependence of the mass of electrons upon their velocity. Considered with hindsight, they were relevant for the rela- tivistic dependence of mass on velocity — although they issued in the erroneous refutation of this dependence [Hon 1995, 194-195], [Cushing 1998, 210-215]. Mass in Lorentz and mass in Einstein are incommensurable quanti- ties (see section 5). Still, Kaufmann’s findings were taken to be relevant for both classical electrodynamics and special relativity. The measure- ment was performed by registering electron trajectories in electromag- netic fields. The electron paths were detected using a photographic plate. Kaufmann managed to obtain a visible curve on the plate whose precise shape was supposed to indicate the sought-for quantity. This effect was positively identified irrespective of the theoretical background. The re- liability of the result was contentious, to be sure; actually, it was aban- doned later. But this issue had nothing to do with the dissent as to the overarching background principles. Lorentzians and Einsteinians had no trouble identifying the traces left by incident electrons.

3The pages mentionned are the ones of the german edition. 90 Martin Carrier

Another case in point is the Kennedy-Thorndike experiment of 1932 which constituted a refinement of the Michelson-Morley experiment and was undertaken so as to compare Lorentz’s and Einstein’s theories em- pirically. Lorentz’s account entailed a negative result of the Michelson- Morley experiment only on the condition that the lengths of the inter- ferometer arms were equal (when unaffected by the motion through the ether). Only under such circumstances, the changes in the velocity of light induced by the motion of the observer and the contraction of optical apparatus canceled each other out precisely. Interferometers equipped with unequal arms, by contrast, should exhibit a net effect. Electrody- namic theory yields an equation that connects the ensuing shift in the interference fringes with the difference in the lengths of the interferom- eter arms (resting in the ether) and the velocity of the apparatus with respect to the ether. The prediction was that if these two quantities did not vanish, a shift should occur during the seasonal change in the direction of the Earth’s motion. The reason is that however the Earth moves precisely through the ether, it cannot be at rest all the time (see section 4) [French 1968, section 3.1; 3.6]. The partisan of classical electrodynamics may feel free to determine the relevant quantities in whichever way she prefers. The point is that the circumstances can easily be arranged such that her theory entails the appearance of fringe shifts. The only thing she has to acknowledge is the unequality of the interferometer dimensions and the attribution of a non-vanishing absolute velocity to the Earth. The realization of the former condition can be left completely to her, the fulfillment of the latter follows from her theory. By contrast, the adherent of special relativity anticipates that no fringe shifts occur. From his point of view, the Kennedy-Thorndike experiment is but a trivial modification of the Michelson-Morley experiment so that the same null result can safely be expected. As it turned out, the prediction of the latter was confirmed and the expectation of the former disappointed. The crucial aspect is that the success or failure of the empirical test may be judged against the background of one’s own commitments and standards. No need for translation arises. A theory may well be tested by its own followers, and to them the relevant claims are by no means obscure4. To be sure, it is necessary that a shared realm of relevant phe-

4Intersubjective control of theories containing incommensurable concepts is still feasible. Kuhn rightly distinguishes between translation and language acquisition [Kuhn 1983, 676-677]. It is a consequence of the context account that concepts can be learned by familiarizing oneself with the pertinent theoretical context. One may become bilingual — and yet be at a loss to translate. It follows that the empirical Semantic Incommensurability and Empirical Comparability 91 nomena is recognized. Advocates of each theory have to acknowledge re- sponsibility for coping with these phenomena (which may be disparately understood in either theory). But this much of a common ground is secured by the mere fact that we are dealing with incommensurable the- ories.

7. Theoretical Contrast and Partial Overlap of Natu- ral Kinds

These considerations make the relations between incommensurable con- cepts more perspicuous. The translation failure arising between incom- mensurable concepts is of a particular sort. It is based on incompatibil- ity rather than unrelatedness. Within the theoretical context account of meaning two constraints guide translations: empirical indications and theoretical integration have to coincide. Synonymous concepts need to apply to the same observations or situations and need to be embed- ded at the same time in nomological frameworks exhibiting the same structure. Incommensurable concepts are distinguished by the fact that there is some agreement on both counts. In order to qualify as prima- facie analogues and candidates for translations, such concepts need to be applicable to some shared domain and display some relatedness as to theoretical integration. I underscored earlier that incommensurable concepts do not satisfy both these demands. But the converse aspect de- serves emphasis as well: incommensurable concepts exhibit a particular type of relationship to one another; they are connected with one an- other by empirical or theoretical ties. This sort of connectedness makes translation failure due to incommensurability a distinctive notion. Let me explore these connections a bit more thoroughly. Kuhn’s notion of a partial overlap among the referents of incommensurable con- cepts provides a basis for further clarification. This notion suggests that incommensurable concepts need to share some domain of application, on the one hand, but that this core domain is expanded in different ways for each of the conceptual counterparts in question, on the other. This means that incommensurable concepts do not denote precisely the same states of affairs. There is a shared realm of application and there are deviations. Take the Lorentz-Einstein example. Although the two theo- ries accept the same measuring procedures for spatiotemporal and mass relations, the predictions regarding these relations do not always agree. comparison of theories with incommensurable concepts can be performed by a single person [Carrier 2001, 85–86]. 92 Martin Carrier

Rather, as I argued before, differences in judgment about the prevailing length relations obtain. It makes a difference, after all, whether the ex- pected contraction relations are reciprocal or asymmetric (see sections 4-5). The point is, then, that these divergent anticipations cannot be brought into harmony because of an underlying theoretical dissent. Lorentzian electrodynamics and Einsteinian special relativity disagree over the appropriate natural kinds (see section 5). The accepted re- lations of similarity diverge in both accounts, with the result that it is impossible to define conceptual analogs of Lorentzian spatiotempo- ral and mass terms in Einstein’s theory. It is a distinctive feature of incommensurability that the relevant classificatory discrepancies resist reciprocal adaptation because they arise from fundamental theoretical divergence. Non-translatability due to incommensurability is not the result of a simple conceptual gap. Incommensurability is not about an accidentally missing word; it is rather about an in-principle rift. Un- derlying incommensurability is a theoretical dissent which makes it im- possible to conceive an ersatz concept that could play the empirical and theoretical role of a term of the other theory in question. There is no way to define a something akin to “absolute motion” or “total mass” in special relativity short of running into a contradiction with the principles of this theory. Consequently, not any old taxonomical disagreement is sufficient for producing incommensurability. Rather, the relevant sort of disagreement needs to be induced by theoretical contrast and resist easy resolution. Consider Kuhn’s own example of a shift in meaning and reference of the concept “planet” as a result of the Copernican Revolution. Geo- centrically speaking, “planet” means celestial body rotating around the Earth. Mars, Sun and Moon equally qualify as planets in this sense while the Earth does not. Heliocentrically speaking, “planet” means celestial body revolving around the Sun. According to this changed understand- ing, Earth and Mars pass as planets, while neither Sun nor Moon do. These changes in meaning are intertwined with a shift in the taxonomy of the relevant bodies. Geocentrically, Mars, Sun and Moon form part of the same natural kind, whereas the Earth was placed in a different category. After the revolution, Earth and Mars were equal in kind, while Sun and Moon shifted in kind in becoming a star and a satellite, respec- tively. The members of the geocentric kind “planet” were scattered into distinct taxa and placed alongside entities which were formerly taken to be of heterogeneous nature [Kuhn 1962, 115; 128-129], [Kuhn 1987, 8]. This example of Kuhn’s regarding incommensurable concepts illus- Semantic Incommensurability and Empirical Comparability 93 trates, first, that such concepts share a core domain of application. A large number of geocentric planets are also heliocentric planets and vice versa. Second, this core domain is expanded differently for the two con- cepts. Geocentric planets include the Sun and the Moon, heliocentric planets instead encompass the Earth. It follows that the two domains of application overlap only partially. Third, this classificatory discrep- ancy resists resolution because of the underlying theoretical contrast. It is this contrast which makes it impossible to reciprocally assimilate the two domains and to apply the concept indiscriminately to all entities in question. This incompatibility between the theories involved lies at the root of incommensurability.

8. Conclusion

There are three conclusions to be drawn from these considerations. First, incommensurability is real. The notion can coherently be reconstructed and positive instances of theories with incommensurable concepts can be specified. Second, incommensurability does not pose a serious threat to the objectivity of science or its commitment to experience. In order to make their conception non-trivial, advocates of incommensurability have to grant — in contrast to their declared intention — that empir- ical comparison of theories with incommensurable concepts is possible. Third, incommensurability is of lasting importance as a problem in the philosophy of language. Incommensurability gives rise to the translation problem associated with the context account of meaning. It constitutes the successor problem to Quine’s indeterminacy of translation. Whereas Quine’s claim was based on the verification theory of meaning, Kuhn’s and Feyerabend’s views emerge within the context account. And whereas Quine is prepared to accept a large number of distinct but equally ap- propriate translations, Kuhn and Feyerabend suggest that there is not a single adequate rendering. Thus, basis and substance of the two posi- tions are fairly disparate. Incommensurability is the follow-up paradox of translation which continues to haunt us after the demise of verifica- tionism. Fourth, in one respect incommensurability continues to be of epistemic significance. My argument does nothing to defuse the above- mentioned worry that incommensurability contributes to undermining a cumulative view of scientific progress according to which science man- ages incessantly to pile up truths upon one another. The lesson incom- mensurability teaches is that in the course of theory change, scientific achievements may be conceptually reframed beyond recognition. In par- ticular, the occurrence of reference shifts poses a serious threat to the 94 claim that scientific theories accomplish an ever deeper understanding of the same objects and processes. In this respect the incommensurability thesis retains some epistemic significance after all. Two brief remarks on Martin Carrier’s paper

André Coret LPHS, Nancy, France

The first remark is the following: is Martin Carrier’s reflection on incommensurability relativistic or realistic? A short sentence stroke me: “incommensurability is real”. It is like a profession of faith and I know that Kuhn never defines himself as a relativist but as a realist. However I am forced to recognize that, in comparing the theories of Lorentz and Einstein, Martin Carrier never uses the term false or true. If I understand his point of view, he considers that the two theories were a priori relevant. As a physicist, I think that the Lorentz theory was false and that the Einstein theory is true. When Lorentz supposes that the initially spherical electron becomes, when it moves a flattened ellipsoïd due to the action of the ether, it was simply a misconception. And Poincaré, in his desire to save the hypothesis of Lorentz, tried also to analyse the interaction of the electron with ether in the same terms. They considered both that the contraction of distances was due to a mechanical effect and consequently were unable to construct a theory which facts which hold together. Even if they deduced the exact shape of the so-called “Lorentz-transformations” (and that just before Einstein), their goal was restricted to a verification of the relevancy of the Maxwell equations of electromagnetism. On the contrary, Einstein was true when he deduced the Lorentz transformations as a result of the attempt to measure distance and du- ration between events from different point of view, from different frames.

Philosophia Scientiæ, 8 (1), 2004, 95–96. 96 André Coret

So, cannot we say that incommensurability could be a mask for hid- den relativism (in the sense of philosophy of science)? My second point is to agree with Martin Carrier and Kuhn about the semantic perturbations which arise during the passage from a theory to a new one. For Martin Carrier, these semantic perturbations result in the untranslatability of the two competing theories : indeed, between Lorentz and Einstein, it was like a dialogue of the deaf. However, let me give two other examples where I consider that the situation is less clear. In 1925, Werner Heisenberg was the first to realize the passage from the theory of quanta (Einstein, Bohr) to the quantum theory: a system is no more described in terms of a representation which is always an intuition (Anschauung) of the reality, but in terms of symbolic entities : Heisenberg and Born used matrices, Schrödinger wave functions, Dirac bra and ket vectors. These entities play the same role in the theory. In spite of a “representation” (Vorstellung), we have a “representant” (Repräsentant). This shift is quite explicit in the papers of Heisenberg and Dirac but appears as problematic in the papers of Schrödinger. I think that it plays an important role in the birth of the quantum theory and constitute a kind of epistemological rupture. Instead of the word “shift” which is used by physicists to analyse the changes in wavelength of the lines in spectroscopy, it is perhaps more relevant to use the term “displacement’ (Verschiebung) employed by Freud in his first topic. Second example : a few years after the birth of quantum theory, chemists began to be interested by using this theory to describe diatomic or polyatomic molecules. A physicist of Göttingen, Friederich Hund, and an american physico-chemist, Robert Mulliken, invented the theory of molecular “orbitals”. They explicitly abandoned the term “orbit” used by Bohr to describe the trajectories of electron around nucleus. This small displacement indicates that it was incorrect to localize electron but that it is only possible to deduce the more probable zone where you can find it. I took these two examples to show that this notion of displacement entails the fact that it is possible to translate the concepts of the theory of quanta in the quantum theory. Saving Incommensurability: Semantic Theory of Meaning or Semantic Theory of Science?1

Soazig Le Bihan LPHS, Université Nancy 2; Universität Bielefeld

Résumé : L’article de Carrier a pour but principal de reconstruire la notion d’incommensurabilité sur la base de la théorie contextuelle de la signification. C’est cette reconstruction dite sémantique que je discuterai ici. La stratégie de Carrier consiste à exhiber deux cas d’incommensurabilité sur la base d’une preuve symétrique d’intraductibilité, elle-même fondée sur la distinction entre deux éléments déterminant la signification d’un concept. Je montrerai princi- palement que la symétrie de l’argument est fautive et que la distinction sur laquelle il est fondée ne tient pas. J’argumenterai ensuite en faveur de la reva- lorisation d’une notion qui joue un rôle secondaire dans l’argument de Carrier, savoir « l’ensemble des situations dans lesquelles le concept est correctement appliqué », tant pour la détermination de la signification d’un concept que pour l’évaluation de la notion d’incommensurabilité. Je tenterai d’ouvrir enfin une autre voie pour la reconstruction de l’incommensurabilité, fondée, non pas sur la théorie sémantique de la signification, mais sur la théorie sémantique des sciences. Abstract: Carrier’s paper is mainly a defence of incommensurability as “a sen- sible notion”, on the basis of the context theory of meaning. I shall here discuss

1Comment on Martin Carrier, “Semantic Incommensurability and Empirical Com- parability: the Case of Lorentz and Einstein”. I would like to thank Robert Nola, as well as Anouk Barberousse, who have both offered comments and advice, and forced me to present my ideas in a much clearer way, even if they are certainly not the ones to blame for the theses developped here, of which I take on the responsability.

Philosophia Scientiæ, 8 (1), 2004, 97–105. 98 Soazig Le Bihan his semantic reconstruction of the notion. His argument consists in exhibit- ing cases where incommensurability is instantiated thanks to a symmetrical proof of untranslatability, based on a distinction between two determinants of the meaning of a concept. I shall mainly show that a logical asymmetry in the distinction hinders the argument from achieving its goal. I shall then defend that a notion that plays a secondary role in Carrier’s argument, i.e. “the set of situation to which a concept is properly applied”, should be placed at centre stage for the determination of the meaning of a concept and thence for the appraisal of the notion of incommensurability. I shall finally sketch an alternative reconstruction of the notion of incommensurability, based on the semantic view of science instead of the semantic theory of meaning.

The aim of Carrier’s paper appears to be mainly a defence of in- commensurability as, I quote, “a sensible notion”. At the end of the paper, Carrier briefly sketches an answer to the usual misunderstand- ing of incommensurability as implying empirical incomparability. But it is unclear whether this is logically linked to the earlier parts. What is really at stake in the paper is the existence and the coherence of the very notion of incommensurability. The core of the paper is constituted by the attempt to prove that the context theory of meaning provides a good basis for a sound reconstruction of incommensurability. I will not discuss whether the sound and clear reconstruction of the notion of incommensurability is possible, or even needed, for Kuhn’s work. Nor will I cast doubt on the thesis that incommensurability does not imply empirical incomparability and relativism of theory choice. However, I am not completely convinced by Carrier’s reconstruction of incommensurability on the basis of the context theory of meaning. More precisely, his argument hinges on a distinction between two determinants of the meaning of a concept. With this distinction in hand, he tries to construct a symmetrical argument, to prove that some cases of incom- mensurability, understood as untranslatability, are instantiated in the history of science. I shall mainly show that there is a logical asymmetry in the distinction that hinders the argument from achieving its goal. I shall then defend that the notion of “the set of situations to which a con- cept is properly applied” is, and appears to be in Carrier’s case studies, more central for the determination of the meaning of a concept than the two determinants he gives us. I shall then try to give an alternative basis for a reconstruction of the notion of incommensurability. The idea is that using a context view on meaning is going the right way, but is still not enough. It is going the Saving Incommensurability 99 right way, because it takes scientific theories as wholes, in which concepts are integrated. It is not enough, because it still takes the translatability of concepts, and not the congruence of structures, as a primary basis for theory comparison. My proposal is that the semantic view of sci- ence may be a better basis. It could offer a simple way to understand incommensurability.

1. Carrier’s symmetrical argument Carrier’s argument is based on the context theory of meaning, from which he deduces a context theory of translation. He gives a sketch of it in section 2. If one looks at Carrier’s summary of this section (p.77), everything seems quite clear: On the whole, then, the theoretical context account recognizes two chief de- terminants of the meaning of concepts. First, the inferential integration of a concept which is specified by its relations to other concepts. The integra- tion of scientific concepts, in particular, is furnished, among other things, by the relevant laws or theories. Second, the conditions of application which are determined by the set of situations to which a concept is thought to apply (or not to apply respectively). To these two sources of meaning correspond two constraints on adequate translations. Rendering a concept appropriately demands, first, the preservation of the relevant inferential relations, and, second, the retention of the conditions of application. In this paragraph, Carrier precisely defines two determinants of the meaning of concepts: the inferential integration (call these (ii)) and the conditions of application (call these (ca)). To these correspond two crite- ria for a good translation, that is, the preservation of each determinant. This distinction is of high importance for Carrier’s argument. It serves as a basis for his comparison between concepts of Lorentzian and Einsteinian theories. Indeed, he wants to prove that there are concepts from the two theories that are not translatable from one to the other, and hence that semantic incommensurability holds between them. Case 1 deals with velocity, case 2 with mass. In both cases, Carrier’s argument proceeds in two symmetric stages, each of which shows that satisfaction of one of the requirement implies dissatisfaction of the other one. The first one is to translate according to the relevant conditions of appli- cation. That is, the two terms are applied under the same circumstances. (. . . ) The catch is that the corresponding predicates do not exhibit the same inferential relations. (. . . ) The second option is to translate such that the inferential relations are retained. But, (. . . ) the conditions of application fail to be preserved. 100 Soazig Le Bihan

Let me call the criteria P (ii) and P (ca) respectively, the preservation of the inferential integration and the conditions of application, then the form of Carrier’s argument is as follows. First, translation based on P (ca) implies a translation failure under P (ii) requirement: P (ca) → ¬P (ii) (1) Second, translation based on P (ii) implies a translation failure under P (ca) requirement: P (ii) → ¬P (ca) (2) Hence, translation is hindered, while semantic incommensurability holds and is finally proved to be “real” or “instantiated”. Thus, the distinction given above is the very basis of the argument’s structure.

2. The symmetry defeated

Now, consideration of the details of section 2 will show that the situation is more confused than it appears at first. In particular, the role given to the notion of “set of situations to which a concept is thought to apply”, in regard to the determination of meaning, is far from clear. Let us call (ss) this “set of situation (. . . )”. More precisely, I shall show how the argument fails because of the relation of (ss) respectively to (ca) and (ii), that makes the neat distinction fall apart. In the passage quoted just above, we read that the second chief de- terminant of the meaning of a concept is “(. . . ) the conditions of appli- cation which are determined by the set of situations to which a concept is thought to apply (or not to apply respectively)”. According to this, (ss) is linked with (ca) in the following way: (ss) determines (ca). (ss) then has logical priority over (ca), so that we can now write, as Carrier suggests: (ss) → (ca) (3) Now in the first paragraph of the same section, we were given that (ss) is linked with (ii); but this link is not very clear:

(. . . ), the meaning of a concept is determined by its relations to other concepts and the meaning of a statement results from its integration in a network of other statements. Another way of putting this is to say that Saving Incommensurability 101

the use of a concept determines its meaning. What a concept means is represented by the way in which it is applied to different situations. The use of scientific concepts is specified by the laws of nature in which these concepts figure. The meaning of a concept like “electric field” is given by its lawful connections to related concepts such as electric current, charge or magnetic field. The concept “electric field” is understood if it is known, for instance, that such fields are produced by electric currents or variable magnetic fields and generate changes in the motion of charges, and so forth. Laws and theories supply a concept with a network of relations to other concepts, and this network determines to which situations the concept is properly applied. Such generalizations add to the meaning of the relevant concepts (my italics and underlining).

The second sentence seems to hold that (ii) and the “use” of a con- cept are strictly equivalent as to the determination of the meaning of a concept. The third sentence obviously aims at defining the term “use”, giving (ss) as its definition. As a consequence, one can say that (ii) and (ss) are equivalent as to the determination of the meaning of a concept.

(ss) ↔ (ii) (4)

However, when Carrier turns to scientific concepts in the last italicised sentence, the relation seems to lose its simplicity: now (ii), that is, the laws and theories for a scientific concept, “specify” (ss). Thus, (ii) is given logical priority over (ss), and this can be now expressed:

(ii) → (ss) (5)

But now it follows from (3) and (5) that the inferential integration of a concept determines its conditions of application, at least in the case of the scientific concepts with which we are dealing here:

(ii) → (ss) → (ca) (6)

Two morals can be drawn from this. First, these considerations cer- tainly point to the ambivalent role given to (ss) in the determination of the meaning of a concept in Carrier’s paper, although he never seems to notice it. We proved in (3) that, following Carrier, (ss) determines (ca). Moreover, independently of Carrier’s consideration of scientific concepts, we had indeed obtained an equivalence of (ii) and (ss) as to the determi- nation of the meaning of a concept. Nevertheless, in his paper he gives (ss) a secondary role and not the central role it may deserve. But let us deal with this point in the last section. And before that, let us see how many doubts these logical considerations raise about the validity of the argument we set out in the first section. 102 Soazig Le Bihan

The argument was based on the independence of, and the symmet- rical roles, of (ii) and (ca). But since an asymmetrical relation holds between these, the argument seems not to be valid anymore. In particu- lar, the second wing is not even logically possible, for one cannot have, at the same time, sameness, or preservation of, the inferential integration and difference in the conditions of application if the latter is determined by the former:

Coming from (6): (ii) → (ca) Thus: P (ii) → P (ca) Which implies the impossibility of the reasoning:

P (ii) → ¬P (ca) (2) that is, the second wing of the argument. Thus, the nice symmetrical structure of Carrier’s argument falls apart. A closer look at the details of these alleged symmetrical wings in the sections concerning the case studies will show that both have really the same form: whether the preservation of (ii) or (ca) holds or not, the chief determinant of meaning and translation criterion is (ss). In the next section, (ss) will be shown to play this central role. I shall then defend the idea that the semantic view on science provides a better basis for incommensurability than the context theory of meaning does.

3. Modelling incommensurability?

Reading Carrier’s case studies section, one becomes aware of the fact that the chief determinant of the meaning of a concept is not the infer- ential integration and/or the conditions of application, as defined in the previous sections, but rather the “set of situations to which it is properly applied”. Let us focus on the respective first stages of the translation attempt to see how this notion is central even in Carrier’s argument1. The structure of the argument here appears far less clear than Carrier wants us to believe. Let Carrier be our guide:

The first try is to focus on conditions of application and to translate ac- cording to equality of measuring procedures: quantities that are determined empirically in the same way can be translated into one another.

1We already dealt with the second stages (or wings) in section 2, showing that Carrier seems to contradict himself. Saving Incommensurability 103

In this first paragraph of the translation attempt, Carrier poses the measuring process to be the conditions of application, as determining the meaning and serving as a basis for the translation of a scientific concept. The beginning of the following paragraph stays with what was announced:

However, the inferential relations fail to be retained.

However, the justification of this statement is rather surprising, for it concludes indirectly to the difference in theoretical integration, on the essential basis of the study of “relevant types of situations”:

The disparate conceptual integration of the seemingly identical concepts of length and velocity becomes conspicuous once the relevant types of sit- uation, as they emerge in the Lorentzian framework, are reconsidered in Einsteinian terms. (My italics)

A list of those situations then follows, and Carrier’s argument hinges on the accurate study of them. Finally, Carrier concludes:

Such differences in judgment indicate a change in the theoretical integration of the concept of length. (My italics)

In this passage, (ca) and (ii) only play a secondary role: what really serves as a criterion for a good translation is here called the “relevant types of situations”, that is (ss). We find ourselves with three determi- nants of the meaning of a scientific concept: the theoretical integration (ii), the types of situations to which it applies (ss), and the processes by which it is measured (ca). No doubt that the last sentence quoted suggests that there holds a priority relation from the highest (theory) to the lowest level (measurement) of the determinants of meaning such as in (6): the sentence says namely that a difference in (ss) has served as the sign (“indicates”) of the difference in (ii). This can be interpreted as follows: the non-preservation of (ss) implies the non-preservation in (ii), which is consistent with (6). Nevertheless, it seems to me that only the second level, that is the “relevant types of situations”, has been useful in the practical determi- nation of the meaning of the Lorenztian and Einsteinian term ‘velocity’. So that (ss) could be the main determinant of the meaning of a concept after all. In that case there would be no need of any shaky symmetrical argument to save the notion of incommensurability, especially if this ar- gument hinges on the distinction between the inferential integration (ii) 104 Soazig Le Bihan and the conditions of application (ca), finally identified, in the case stud- ies, with the old, “orthodox” and controversial distinction between the theoretical integration and the measuring processes of a concept. The study of the relevant types of situations to which a concept applies would then be the key to prove that incommensurability is a sound notion. An analogous (short) analysis can be conducted on the second case study about mass. Here again, Carrier narrows the scope of the con- ditions of applications to the measuring processes. Then he uses the ways in which the two theories “capture [a] situation” (p.10) (my italics) as sufficient determinants of the meaning of the concept they include. Finally the difference in these ways is considered as a sufficient reason to draw the conclusion that there must be a difference in its theoretical integration. In the end, Carrier’s first distinction between two deter- minants of meaning does not play the role it was supposed to play in the case studies. On the whole, the meaning of a concept appears to be sufficiently determined by the “set of situations”, or maybe better to say “the relevant types of situations” to which the concept applies. Probably the late Kuhn’s theory of kinds would appear as the natural development of my argument here. And in fact, section 5 of Carrier’s paper does refer to it, and appraises his view on incommensurability in contrast with it. Here Carrier applies the same bottom-up type of argument to give a secondary role to the change of taxonomies of natural kinds between theories as when he dealt with the ways in which theories capture relevant types of situations to which the concept applies.

Incommensurable concepts emerge if, owing to nomological change, natural kinds are restructured. If a new system of laws is adopted that conflict with a previous one, the former equivalence classes split up into heterogeneous components and realign to form new taxonomic structures. This change of the class of properties to which a concept is rightly applied goes back to a change in the nomological integration of this concept. The use of electrodynamic and relativistic concepts is governed by contrasting sets of laws. It is this nomological contrast that constitutes the ultimate reason for the translation failure. The dissolution and the new formation of natural kinds which is placed at center stage by Kuhn is a proximate reason that follows from the divergence of the relevant inferential relations. (My italics)

I will not go further in the discussion and appraisal of the late Kuhn’s theory. So let me, as an end to this already too long comment, run the risk of giving an alternative proposal. It seems to me that Carrier’s notion of “theoretical”, “nomological”, or “inferential integration” is not clear enough. At first (see (4)), it was equivalent with the set of situations 105 to which a concept properly applies. At a second stage Carrier tried (see (5)) to give it a logical priority. But then the risk is, as in the first stage of the first case study, to go back to the orthodox distinction that I am sure Carrier does not want to defend. That may be the reason why he distinguishes in parenthesis (see p.85) his notion from the simple mathematical formulas in the second case study, maybe feeling the old orthodox theory lurking behind his words. More seriously, the notion is either too broad or too narrow, and I claim that the chief determinant of meaning appears to be “the relevant types of situations to which a concept is properly applied”, throughout the paper. And I doubt that the bottom-up movement from these, or from Kuhn’s taxonomies, sheds clearer light on the notion of incommensurability. I now risk the proposal that the notion of “the relevant types of situa- tions to which a concept is properly applied” is the linguistic formulation of what an advocate of the semantic theory of science would call a model. Shifting then from semantic theory of meaning to semantic theory of sci- ence, we could hope to find an alternative, sound reconstruction of the notion of incommensurability. Since two theories can be represented by the set of their models, semantic incommensurability could find a natu- ral definition as the lack of congruence of some of these models, that is, the lack of a relation of equivalence between these models that would be incompatible as regards to internal structure. Looking back to Lorentz electrodynamics and Einsteinian special relativity, it is interesting to consider that noting, as Carrier does p.80, that

Lorentz-contraction proper is asymmetric whereas Einstein-contraction is reciprocal would be then sufficient to conclude to semantic incommensurability: the two theories are at least partly incompatible as regard to internal structure. Carrier’s case studies could be then interpreted as providing two examples of this incompatibility, concerning velocity and mass. But this is going far too fast. However, this may deserve further investigation. The only claims I would defend are the following. First, Carrier’s argument does not have the nice symmetric form he wants to give to it. Secondly, the distinction on which the argument hinges is neither clear enough, nor sheds a brand new light on the notion of incommensurability. And thirdly, the relationships between the inferential integration and the set of situations to which a concept is properly applied could be certainly fruitfully clarified. 106 Characterizing Incommensurability on the basis of a contextual theory of language Conditions of Application and Inferential Relations in M. Carrier’s Reconstruction of Incommensurability

Léna Soler LPHS, Nancy, France

Résumé : l’article, tout d’abord critique certains aspects de la manière dont Martin Carrier caractérise l’incommensurabilité sémantique à partir d’une théorie contextuelle du langage, puis introduit des distinctions et fait des propositions en vue de poursuivre le même projet. On soutient que deux conceptions différentes de la notion de ‘conditions d’application’, et corréla- tivement deux acceptions distinctes de la clause ‘préservation des relations in- férentielles’, sont à l’œuvre dans la caractérisation de Carrier, et que sa thèse centrale ne tient que grâce aux déplacements de sens correspondants. On sug- gère de remplacer cette thèse — selon laquelle les concepts incommensurables sont ceux qui sont intraduisibles au sens spécifique où ils ont soit mêmes con- ditions d’application soit mêmes relations inférentielles mais jamais les deux à la fois –, par une caractérisation qui, d’un point de vue méthodologique, accorde une primauté aux relations inférentielles. Cette caractérisation est pour l’essentiel constituée : d’une part de la thèse (kuhnienne) selon laquelle les concepts incommensurables sont avant tout ceux qui présentent des rela- tions inférentielles largement non superposables ; d’autre part d’une analyse des liens existant entre relations inférentielles et conditions d’application, en particulier d’une réflexion sur les conditions auxquelles certaines relations in- férentielles peuvent et doivent être identifiées à des conditions d’application. Abstract: In this article I present, first, a criticism of certain aspects of the way Martin Carrier characterizes semantic incommensurability on the basis of

Philosophia Scientiæ, 8 (1), 2004, 107–152. 108 Léna Soler a contextual theory of language. Subsequently I introduce some distinctions and put forward some proposals in order to pursue the same project. It will be argued that two different conceptions of the notion “conditions of applica- tions” and, correlatively, two different meanings of the clause “preservations of the inferential relations”, are involved in Carrier’s characterisation, and that his central tenet holds only thanks to the corresponding meaning-shifts. Ac- cording to Carrier’s thesis, the incommensurable concepts are those that are untranslatable in the following specific sense: they have either the same con- ditions of application or the same inferential relations, but they never satisfy both determinants at the same time. I suggest to replace this thesis by a characterisation that, from a methodological point of view, grants logical pri- ority to the inferential relations. This characterisation is mainly based: on one side on the Kuhnian claim that the incommensurable concepts are those who have largely non superimposable inferential relations; on the other side on an analysis of the links between inferential relations and conditions of applica- tion, particularly on a reflection concerning the conditions under which some inferential relations can and should be equated with conditions of application.

Incommensurability is one of the most controversial issues of 20th century philosophy of science1. It has to be said that lack of clarity af- fecting so many discussions about the incommensurability problem tends to hide the real difficulties that we encounter when we try to characterize precisely what is at stake. In this landscape, the work of Martin Car- rier (MC) provides a welcomed, painstaking and stimulating attempt to characterize semantic incommensurability and its epistemological conse- quences2. MC gave two talks on the topic in France in March 2003, first in Nancy, at the Poincaré Archives, and then in Paris, in the seminar on incommensurability that I direct at the International College of Phi- losophy. I learned a lot from these talks and from the live discussions surrounding them. The present paper is a very extended version of the short commentary of MC’s talk that I presented in Nancy. As every philosophical work, it includes also critical remarks: without any doubt, this seems to me the best way to pay homage to MC’s work. In this paper I will, to start with, bring to the foreground a few points: I will state (here without further justification) a few fundamen-

1See [Hoyningen 1989]; [Sankey 1994]; [Hoyningen & Sankey 2001]. 2Cf. [Carrier 2000], [Carrier 2001] and [Carrier 2002], in addition to the paper contained in the present book. The critical analysis I will propose here is not just about the later paper: it aims to cover MC’s different contributions to the incom- mensurability problem. Incommensurability on the basis of a contextual theory of language 109 tal assumptions, that seem to me, after many years of research on the topic, to be required in order to achieve a deep and articulated charac- terization of semantic incommensurability. This will make possible to emphasize some fundamental points of agreement between MC and me, since we converge about the very essentials, and will at the same time provide the framework for further discussion. In a second moment, I will discuss some aspects of MC’s work with which I feel uncomfortable. And in a third moment, I will suggest some ways in order to refine the characterization of incommensurability according to the same project. The reader will find a list of notations at the end of the paper.

1. Some fundamental assumptions in order to under- stand the incommensurability/commensurability prob- lem

First, I of course assume, in agreement with MC’s work (and in opposi- tion to the thesis that incommensurability is an invention of philosophers of science), that semantic incommensurability is a real and historically instantiated phenomenon. Second I think, as MC does, that we must rely on actual historical cases to elaborate and test our characterization of incommensurability (even if disagreements can of course arise about what ‘actual historical cases’ are and tell us). Third I think, with MC, that semantic incommensurability names a deep conceptual restructuring. That is, we admit that there are indeed scientific revolutions, that revolutions are deep conceptual reorganisa- tions, and that incommensurability labels the relations, to be character- ized, between the initial and the final conceptual frameworks. Forth, we agree that to admit revolutions and incommensurability is not to say that there is nothing in common between the two theories considered. Indeed, there are significant common points. More: there must be significant common points; otherwise, we would not consider the two theories as rival incommensurable theories, but as theories pertain- ing to two different disciplines, coping with different realms of objects, and in that case, incommensurability would not raise any epistemologi- cal problems (in particular, it would not have appeared to threat theory comparison and realism). I think that this is a very important point, em- phasized by MC in his papers, and also developed in some of my works3. In brief incommensurability, if it is to be of epistemological interest, has

3Cf. MC’s paper, section 6; cf. also the analyses of MC, and the references he gave 110 Léna Soler to label very deep differences arising in the context of subsisting common points between successive theories. To characterize the very nature of these common points is an important aspect of the incommensurability problem. Fifth I assume, again in full agreement with MC, that in order to be able to characterize incommensurability, we need to rely on a theory of language. Of course, this does not imply that science can be reduced to language and that incommensurability can be seen as a purely linguistic phenomenon. Rather, what is stressed is that that human science always involves language (ordinary, specialized, or mathematical) and that sci- entific revolutions indeed involve linguistic changes. Therefore, we must examine closely these linguistic changes and, for this purpose, we need a theory of language. Sixth, I am convinced, as is MC, that the required linguistic theory has to be a contextual, holistic one. In other words, we acknowledge that science works as a system and that there are structural aspects of scientific practices, and we focus on the linguistic dimension of this assumption. Few years ago, I tried to understand incommensurability with the aid of a theory inspired by Ferdinand de Saussure’s structural linguistic4. Now I think that MC’s attempt to rely on a contextual theory inspired by Wittgenstein, Hanson and W. Sellars is more promising5. Indeed, MC’s contextual theory seems to be more suitable to take into account the relations between the linguistic structures and the empirical world. This is precisely the role played by what MC calls “conditions of application”. Seventh, and last, I agree with MC that — as Kuhn himself re- peatedly pointed out — incommensurable theories are not empirically incomparable6.

2. Two different notions of “CA” in MC’s analysis: CA1 and CA2 The distinction between conditions of application (CA) and inferential relations (IR), and the idea that a good translation must satisfy both of Feyerabend, Laudan and Papineau in [Carrier 2001, 83-84]. Cf. also [Soler 2003] and [Barker 2001, 250]. I already stated the problem and stressed its importance in the introduction. 4[Soler 2000b]. See also [Soler 2004b]. 5For a general presentation of the context theory of meaning drawing on such references, see [Carrier 2001, 66-67]. 6Although incommensurable theories generate special difficulties, that have to be taken into account, concerning the task of empirical comparison. Incommensurability on the basis of a contextual theory of language 111 criteria, are at the heart of MC’s characterization of incommensurability. Indeed, according to MC’s central tenet, incommensurable concepts are untranslatable concepts, in the sense that they fail to satisfy at the same time the two conditions imposed on translation, namely, ‘sameness of CA’ and ‘sameness of IR’.

The translation failure of incommensurable concepts arises from the im- possibility to jointly fulfil the two conditions of adequacy that the context theory places on translation. Would be conceptual analogues either fail to maintain the conditions of application or to reproduce the concomitant inferential relations. [Carrier 2001, 77].

The exam of typical examples7

suggest that the type of conflict emerging here is a general feature of in- commensurability [Carrier 2001, 77].

In brief, MC’s definition of incommensurability can be schematically captured by the formula:

Either [(same CA) and non(same IR)], or [(same IR) and non(same CA)].

By analysing the problem of incommensurability with the aid of these distinctions, MC helps us to take a great step forward. However, there is still some work to be done about these distinctions. The first aspect concerns the notion of ‘CA’. This notion is impor- tant, because it has the function to help us to understand how a theory is connected to the world. Thus we absolutely need a notion of this kind. However, it seems to me that different senses of the notion of ‘CA’ are in- volved in MC’s developments, both at the level of general definitions and at the level of the application to particular historical cases. Although it is true that these senses are related, I believe that it is important to explore their differences and to render explicit their mutual relations. First of all, I want to focus on what seems to me the major shift in the meaning of ‘CA’, a shift that, I think, has important consequences for MC’s central conclusion. I will argue that, in what MC names his “first try” and his “second try”, two different (although related) concepts are referred to with the same label ‘CA’. 7In addition of the one analysed in the present volume, MC considers in other papers, other prototypical cases of incommensurable concepts like phlogiston/oxygen, impetus/moment, or geocentric planet/heliocentric planet. 112 Léna Soler

Let us call L1 any linguistic item pertaining to theory T1, L2 any linguistic item involved in theory T2, and so on. By ‘linguistic item’, I mean a signifier or a group or signifiers forming an expression or a sentence. Here are some typical examples considered by MC:

Ex1. T1 = Lorentz’s ED; T2 = Einsteinian SR; L1 = L2 = ‘mass’, or ‘length’, or ‘velocity’.

Ex2. T1 = Lorentz’s ED; T2 = Einsteinian SR; L1 = ‘real mass’, L2 = ‘rest mass’. (ED: electrodynamics; SR: special relativity).

Ex3. T1 = phlogiston theory, T2 = chemistry of Lavoisier; L1 = phlo- giston ; L2 = oxygen.

Let us consider the first try, that is, translation according to sameness of CA. In the first try, MC exhibits two linguistic items L1 of T1 and L2 of 8 T2 that are said to have the same CA . In what sense do they have the same CA? In the sense that L1 and L2 are related to the same empirical situations (in the ED/SR example as described by MC, these situations correspond to identical measurement procedures). Thus ‘CA of L’ mean ‘empirical situations to which L is related in a given theoretical context T ’. Let us call this meaning ‘CA in the first sense’, and let us refer to it as CA1. Let us now consider the second try, translation according to sameness of inferential relations. In his second try, MC exhibits two linguistic items L1 of T1 and L2 of T2 that are said to have the same IR, and he concludes that such items have different CA. In what sense do L1 and L2 have different CA? In order to answer, we have to examine what MC exactly does in the second try. Roughly speaking, he gives a theoretical definition of L1 (resp. L2): he explains the meaning (the sense) of the concepts used by the adherents of T1 (resp T2). That is, he makes explicit the relations of L1 (resp. L2) with (in principle all) other relevant theoretical signifiers of T1 (resp. T2).

8 ′ ′ This is supposed to be the case for L1 = L2 = ‘length’ and L1 = L2 = ‘velocity’, in the context of T1 = Lorentz’s ED and T2 = Einsteinian SR (cf. MC’s paper in the present volume, section 4); or for L1 = ‘phlogiston escape’ and L2 = ‘oxygen bounding’ in the context T1 = phlogiston theory and T2 = chemistry of Lavoisier [Carrier 2001, section 6]. Incommensurability on the basis of a contextual theory of language 113

Then he concludes that L1 fails to apply, that L1 does not apply at all from T2’s point of view. What does it mean in this case? It means that, from T2’s point of view, concept L1 is “empty”, that L1 “is no longer legitimately applied to any phenomenon” [839 ]; it means that “there is no such thing” as what T1 names L1 [Carrier 2002, 136]. In other words, ‘to apply’, in the context of the second try, is equivalent to ‘to refer’ (according to some determined subject or group of subjects). L1 ‘fails to apply’ means that L1 does not refer to anything: that what T1 describes under L1 doesn’t exist according to the adherents of T2.

(And this is so, because the state of affairs that T1 describes under L1 is incompatible with the state of affairs that T2 describes under T2. It is not simply that L1 does not exist according to T2; it is, moreover, that the existence of L1 is inconsistent with T2. What L1 names cannot coexist with T2: it cannot be peacefully grafted on T2, it is incompatible, contradictory with T2).

Hence, in the second try, L1 of T1 and L2 of T2 are said to have different CA, because they cannot both apply in the sense that the two states of affairs they describe cannot both exist: L1 (resp. L2) is, according to the adherents of T2 (resp. T1), an empty name, a description that does not apply to anything, that does not correspond to any real state of affairs in the physical world10. Conclusion: in the second try, ‘CA of L’ means ‘existence of the state of affairs named L’, ‘truth of the statement L’, or, rephrased in a softer way, ‘empirical adequacy of the description named L’. A linguistic item L will be thought to apply, to have CA, if it is thought to label an em- pirically adequate description, a really existing states of affairs, if it is thought to have a counterpart in reality. Let us call this meaning ‘CA in the second sense’, and let us refer to it as CA2 (or let us say that a linguistic item applies2).

A striking way to show that CA1 and CA2 correspond to different concepts, is to point out that one and the same linguistic item, say L1, may apply1 but fail to apply2.

9The pages mentioned into brackets without further reference correspond to the pages of the present volume. 10By the way, the converse holds too, although it is never explicit in MC’s pre- sentation. Indeed MC, in the second try, always describes the situation from the point of view of the recent theory, that is, from the point of view of the adherents of T2. However this has, in principle, no damaging philosophical consequences for MC’s argument, since the converse can be unproblematically stated in MC’s framework. 114 Léna Soler

Indeed, suppose that we are adherents of T2; we think that L1 of T1 does not pick out anything in the physical world (that is, fails to apply2). But nevertheless, we cannot deny that L1 is indeed linked by T1 to some empirical situations. And if we admit the description involved in the first try, we admit that L1 is linked by T1 to the same empirical situations as L2 by T2. In other words, we admit that L1 and L2 have the same CA1. Thus, as L2 indeed applies1, we must conclude that L1 applies1 as well. Therefore, L2 applies1 and does not apply2.

I think that CA1 and CA2 should be carefully distinguished. Al- though CA1 is, in my opinion, the most fundamental and useful deter- minant, we can hope to rely on both CA1 and CA2 in order to achieve a fined-grained analysis of the incommensurability problem based on a more complex and precise operational notion of CA.

3. Two different understandings of the clause ‘trans- lation according to preservation of IR’

I will now consider the notion of IR and the clause ‘preservation of IR’, arguing that two different interpretations of the clause are involved in the first and in the second try. In the first try, L1 of T1 and L2 of T2 are said to have different IR (or theoretical integration), because the theoretical network at the heart of which L1 lies in T1, and the theoretical network at the heart of which L2 lies in T2, are two linguistic systems of very different structures, indeed two incompatible systems (and this is so, as underlined by MC, because L1 and L2 appear in incompatible laws, and thus in non-overlapping classes of kinds, in T1 and T2). Therefore, in the first try, ‘IR of L’ means ‘structure of the theoretical network surrounding L in T ’, or ‘system of the theoretical relations at the heart of which L lies in T ’. Accepting this meaning, it is natural to understand expressions like ‘preservation of the IR of two linguistic items L1 and L2’, as something like ‘same structure of the theoretical networks associated to L1 in T1 and to L2 in T2’. And then it is natural to expect that MC’s second try, that is, the attempt to translate according to the clause ‘preservation of IR’, will Incommensurability on the basis of a contextual theory of language 115 correspond to the search for linguistic items of T1 and T2 that seem, prima facie, to lie at the heart of two similarly structured theoretical networks. However, this is not what MC looks for in the second try. Under the heading ‘translation according to preservation of IR’, what MC does, in his analysis of historical examples, is the following thing: he associates, to a signifier L2 of T2, a theoretical structure different from the one usually associated to L2 in T2, a foreign theoretical struc- ture corresponding to the theoretical network surrounding L1 in T1. In other words, he “grafts” (as he says himself) the structure of relations characteristic of L1 in T1 on a linguistic item of T2. Hence, in MC’s second try, ‘preservation of the IR of L1 from T1 to T2’ means ‘importation in T2, and coordination to L2, of a foreign theoretical network deducted from the incommensurable rival theory T1 and coordinated to L1 in T1’. Conclusion: there are two possible ways to understand the clause ‘translation according to preservation of IR’, and two different associated procedures. Let us mark MC’s procedure in the second try with suffix 2 (to make short: TIR2) and let us mark with suffix 1 the previously sketched procedure, which is involved in the first try, that is, ‘to look for linguistic items that have prima facie similar IR’ (to make short: TIR1).

4. For an other characterization of MC’s second try

I have, so far, successively focused on each constraint upon translation considered in isolation and examined what it became, first when it is in- volved in the first try, then when it is involved in the second try. Keeping the conclusions of these reflections in mind, I want now to switch from ‘constraint entry’ to ‘try entry’: that is, I intend to consider MC’s first and second tries as two unitary wholes linking together both constraints, and, examining each unit one after the other, to discuss MC’s description of them. MC’s account of his first try seems convincing to me. Roughly speak- 11 ing , the first try (t1) shows that in incommensurable theories: (t1a) there are linguistic items which are grounded in the same empirical sit- uations (in my vocabulary: which have the same CA1) and which can

11I say ‘roughly speaking’, because, as it will appear, the clause ‘linguistic items grounded in the same empirical situations’ is indeed vague, and need to be articulated (see sections 5 and 8). 116 Léna Soler then be translated according to this criteria); but (t1b) these linguistic items do not have the same IR, and then, they do not satisfy the second criteria (in my vocabulary: they cannot be T IR1). I’m not so convinced by MC’s account of the second try. More pre- cisely: what is pointed out in this second try is in itself instructive, but should be, I think, rephrased in a more adequate vocabulary — and this is of course not a purely linguistic disagreement. To explain why, let us examine again what is actually done in MC’s second try.

A. Consider the first step of the second try (t2a). This step is described under the label ‘translation according to the preservation of IR’. But as pointed out before, in the second try, we are not looking, in T1 and in T2, for terms presenting similar IR. Indeed in (t2a), we in fact continue to focus on the same linguistic items L1 and 12 L2 that were involved in the first try , that is, on items that are, from the beginning, assumed to have different and incompatible IR (since this is indeed the conclusion of the first try that the linguistic items under scrutiny have different and incompatible IR). Thus in (t2a) we associate to L2 the IR usually associated with L1 in T1: we import in T2 a linguistic network usually pertaining to T1 (or conversely). I do not think that this operation is well-labelled as a ‘translation according to preservation of IR’. Of course, we can identify some reasons why this operation has been associated with the expression ‘preservation of IR’: indeed, the opera- tion consists in focusing on the IR of L1, in ‘preserving’ these IR, and then, in grafting them, untouched, on L2 of T2. But it is nevertheless problematic to interpret this operation as a translation preserving the IR. It seems to me that a translation, even metaphorically understood, should at least entail the idea of the search for an equivalence (of a kind to be defined) between some elements of the two languages (or the two realms whatever they are) under comparison. This being admitted, a successful translation (here according to IR) should mean, if not an identity, at least a sufficiently strong similarity between two linguistic items pertaining to T1 and T2 respectively (here between the IR of these items). As this condition is not satisfied in the case of the linguistic items L1 and L2 involved in MC’s second try (as MC recognizes himself in the conclusion of his first try), I conclude that it is better to reserve the label

12Or almost the same: for ex. in the first try MC considers “phlogiston escape” and “oxygen bounding”, and in the second one, “phlogiston” and “oxygen”. Incommensurability on the basis of a contextual theory of language 117

‘translation according to preservation of IR’ to the operation involved in t1b (that is, to T IR1 = T IR: to look for, and to find if the translation is successful, two linguistic networks of T1 and T2 that possess similar structures, that are superimposable). As for the operation involved in t2a, I will characterize it as a graft (G) of foreign IR: a graft, on a given linguistic item L1 used in a well defined theoretical context T1, of a foreign network of IR (foreign in the sense that the linguistic item L2 associated to this network is customarily used in a theoretical context T2 different from T1, historically separated from T1). Note that to talk about a graft does not presuppose anything about the acceptance/rejection of the graft. In MC’s second try, the rejection of the graft is inevitable, because from the beginning, by construction, the graft deals with incompatible inferential networks. But we can perfectly imagine cases in which successful grafts take place. This happens if the foreign T1 and T2 under scrutiny are, although at first foreign in the sense of empirically separated, nevertheless compatible, additionable (not incommensurable). Whatever label one is ready to use, I think that the operations in- volved in step (t1b) on the one hand (in my notations: T IR1 = T IR), and on the other hand in (t2a) (in my notations: T IR2 = G) should be carefully distinguished. Both could be taken into account in a fined- grained characterization of incommensurability.

B. Consider now the second step of the second try (t2b). Here one provides, for the relation between the two incompatible structures associated to L1 and L2 already involved in the first try, a different description from the one proposed in the first try. This dif- ferent description consists in emphasizing that, according to T2, L1 is empty. And such a description is categorized as a ‘failure to apply’, a failure of the clause ‘translation preserving the CA’. Two remarks can be made about (t2b). First, to emphasize that from T2’s point of view, L1 describes a state of affairs that does not correspond to anything in the physical world, simply amounts to clarify a necessary consequence of the premise of the second try: namely, that the IR of L1 and the IR of L2 are incompatible. Indeed, as it is admitted from the beginning in the second try, at least tacitly, that the two chosen candidates to T IR2 have inconsistent IR, they cannot both refer to existing physical states of affairs (or both be adequate descriptions of the physical world); at least one of them must 118 Léna Soler be empty (or inadequate). In brief, in (t2b), what is actually done, is to continue to focus on the same inconsistent theoretical structures involved in the first try, and then, just to develop a little bit more the clause ‘to have incompatible IR’. Second, the question arises to decide if the judgments of the T2’s adherents (resp. T1’s adherents) about the emptiness of L1 (resp. L2) are well-labelled as judgments concerning CA (in my vocabulary: CA2). At first sight, the present terminological point seems less problematic than the previous one concerning ‘translation according to the preserva- tion of IR’. Indeed, neither of senses MC has given to the expression ‘CA’ stands in opposition with customary contemporary usages. In par- ticular the second sense — the choice to name ‘CA’ what is analysed in t2b, which is what we want now to discuss –, corresponds to one of the ordinary usages of the expression ‘CA’. True, we commonly say that a term ‘does not apply (at all)’ to mean that this term does not name anything existing in the physical world (licorns, for ex.). Now, if we reflect a little bit more on the nature of judgments of the CA2-type, we can feel uncomfortable with the label ‘CA’. Judgments of the CA2-type are, in fact, modal judgments characterizing the status of already available statements holding in a theoretical context T . They are second order judgments about the adequacy and objectivity of some assumptions of T (if not about the independent existence of some states of affairs targeted by T ). They are second order judgments in a chrono- logical as well as in a logical sense: although we can be agnostic about the fact that a word L applies2 when we have specified its theoretical content and the way it is connected to some empirical situations, we must necessarily have the latter specification at our disposal in order to be able to decide if L applies2. Yet, to admit the preceding characteriza- tion is to admit that judgments of the CA2-type can be (and indeed are most of the time in MC’s examples) modal judgments about previously isolated IR. This may render confused the distinction between CA and IR. This being said and kept in mind, I will nevertheless conclude, taking into account customary usages, that the problem, with MC’s notion of CA, is not so much in itself to have labelled ‘CA’ (tout court) what I have isolated as CA2, but to have conflated, under one and the same expression, two operations (my CA1 and CA2) which are not identical and which should be distinguished in the context of the incommensura- bility problem. In what follows I will, for my part, maintain the generic common expression ‘CA’, in order to indicate that there are substantial common points and relations between both determinants, but I will con- Incommensurability on the basis of a contextual theory of language 119 tinue to distinguish with suffix 1 and 2 the two operations involved in the first and the second try, in order to stress the substantial differences spelled out above. Let us recapitulate what is done in the first and second try:

t1a = to look for some linguistic items that have the same CA1; suc- cessful attempt; conclusion: L1 and L2 are translatable according to the CA1.

t1b = to try to translate according to ‘sameness of IR’ (=T IR); un- successful attempt; conclusion: L1 and L2 are have different IR and are not translatable according to ‘sameness of IR’.

t2a = to graft the IR of L1 on L2 and reciprocally (= G, inadequately described as a T IR by MC);

t2b = to examine the CA2 of L1 and L2; conclusion: if L1 have CA2, then L2 does not apply2, and if L2 have CA2, then L1 does not apply2; thus L1 and L2 do not have the same CA2.

More will be said about the substantial common points and differ- ences between CA1 and CA2 (see section 6). But first, we need to reflect again on the notion of CA1.

5. An analysis of the notion of CA1

5.1. Several characterizations of the notion of CA in MC’s analysis of incommensurability

Several characterizations of the notion of CA1 are used throughout MC’s various papers on incommensurability. At the beginning and at a general level, the CA of a term (my CA1) are said to be “determined by the set of situations to which the concept is thought to apply (or not to apply, respectively)” [77]. Subsequently MC uses several different expressions in order to explain the clause ‘same CA’, for instance:

• to be “applied [non accidentally] to the same objects” [76]; to “refer to the same state of affairs” [76];

• to be “applied under the same observable circumstances” ([Carrier 2002, 137], and without the adjective “observable” [85]); 120 Léna Soler

• to be “determined empirically in the same way” ([81], [Carrier 2002, 134];

• to have the “same empirical import” [Carrier 2002, 134];

• to satisfy the condition “equality of measuring procedures”13 [81], [Carrier 2002, 134] (emphasis added);

• to satisfy the condition “equality of measuring indications” [Carrier 2002, 134] (emphasis added);

• to satisfy the condition same “values obtained” [Carrier 2002, 137].

(Most of these expressions also appear in [Carrier 2001]). Are these expressions all equivalent? It is doubtful that the answer could be positive. Particulary with respect to concepts linked to mea- surement practices, one may find natural to ask: is the use of the same instrument sufficient to conclude that the concepts have the same CA? Or do the results of the measurements have moreover to be the same? More generally, what has exactly to be identical, in order to be able to conclude that two words have the same CA? These are not trivial questions and, as we shall see, we will encounter similar problems in the following analysis. Shifting to the analysis of particular examples, we find the same diversity of meaning concerning the notion of CA (CA1). Let us list most of them.

• The term “length” is said to have the same CA (CA1) in the lorentzian and einsteinian frameworks, because “measurements based on rod transport or transmission time of light signals are equally accepted within both theories. That is, classical electrodynamics (ED) and special relativity (SR) roughly agree on the acceptabil- ity of length measurements. Measuring lengths by registering the round-trip travel time of a light signal, as it is done, for instance, in a Michelson-Morley setup is endorsed within the two accounts, and the results of the procedure are unanimously acknowledged as reliable” [81].

13The expression is introduced putting the stress on the fact that the two incom- mensurable traditions agree on the “reliability” of some determined instrument-types and experimental procedures, and thus on the “trustworthiness” of the results ob- tained by the corresponding procedures. Incommensurability on the basis of a contextual theory of language 121

• The CA (CA1) of the lorentzian and einsteinian term “mass” are similar, since “mass is evaluated in the same way in the two ac- counts in question. They both endorse determining mass values using a balance or collision processes (thereby drawing on momen- tum conservation)” [84].

• The CA (CA1) of “phlogiston escape” and “oxygen bounding” “roughly coincide”, since “in most cases in which partisans of the phlogiston theory thought it legitimate to apply the predicate “phlo- giston escape”, adherents of the oxygen theory would speak of “oxy- gen bounding” [Carrier 2001, 75].

• “Impetus” and “momentum” are said to have the same CA (CA1) because “both quantities are estimated by the product of a body’s velocity and its weight or mass” [Carrier 2001, 77].

• In order to spell out the CA (CA1) of the concept of “geocentric planet”, MC lists the relevant celestial objects falling under the concept (Moon, Mercury, etc.) [Carrier 2001, 77].

Without pretending to give an exhaustive analysis of the clause ‘CA of a linguistic item’, I want to distinguish several CA1-types involved in MC’s papers, and to stress some difficulties about the CA1 determinant.

CA CA CA 5.2. Distinguishing several 1-types: 1obj and 1mes

To begin with, let us describe the internal structure (or if one prefers, the ‘grammar’ in a wittgensteinian spirit) of any CA1, and let us fix some notations that will be used all along the paper. Any CA1 may be decomposed in three components:

• The subject of the application (say Sa), which is a linguistic item (a single linguistic item L or a composed one like a sentence or a theory T );

• The point of application (say Pa) or the object of the application, that is, (the description of14) the set of empirical situations (say Eis) to which Sa applies;

14I add ‘the description of’ since I consider the situation from the point of view of the philosopher of science, who have to render things explicit. 122 Léna Soler

• The relation (say Ra) constitutive of the application, that is, (the specification of) the kind of link which is supposed to hold between Sa and the Eis equated to the Pa. Although the ‘application’ lexicon is, as we will see, plastic and vague, not every relation can aspire to be a relation of application. The ultimate motivation for introducing the notion of CA and for distinguishing it from the notion of IR — and, as we said, what makes the interest of the notion of CA — is, basically, the need to name and take into account the non linguistic dimension of science (embodied in our Eis above): the fact that science has the peculiarity to grow in a very intimate relation with extra-linguistic concrete experiences. In agreement with such a motivation, all the MC’s characterizations or in- stances of ‘CA1’ given above have in common, beyond their differences, to target what (in a given state of knowledge) is taken as real empirical situations: either existing phenomena like observable combustions, ob- servable celestial bodies, observable changes in the place and the velocity of macroscopic bodies, etc.; or real available experiments involving real scientists performing real manipulations on real instrumental objects, like mass measurements with the help of a balance, or length measure- ments by means of the Michelson-Morley device, etc. Now, despite the fact that all of MC’s characterizations or instances of ‘CA1’ share the feature to vindicate the rights of the extra-linguistic reality through the targeted Eis, they also manifest striking differences concerning the kinds of Eis involved. • First, the Eis involved are sometimes ‘natural’ and sometimes ar- tificially (experimentally) produced, and they correspond, some- times to naked-eye (or naked-sense) observations, sometimes to highly instrumented observations. • Second, these Eis may be divided into two different types: what I will call the objective Eis (or Eiobj), and what I will call the auxiliary or measuring Eis (or Eimes). – The objective Eis are empirical situations taken to be mani- festations of the object under study (of the physical reality for ex.), and correlatively, taken to provide phenomena that have to be explained by (that are relevant for) theories responsible of this order of reality (physical theories for ex.). – By contrast, the measuring Eis are empirical situations (in modern physics most of the time highly instrumented em- pirical situations) performed in order to determine (most of Incommensurability on the basis of a contextual theory of language 123

the time to measure if we deal with modern physics) some variables defined by one or the other of the available theories about the object under investigation15.

• In other words we have:

– On the one side, situations in which the linguistic item L is supposed to play a significant role (situations exhibited in order to show that the reality named L — whatever it is from an ontological and mathematical point of view — is indeed involved here, and thus that the linguistic item L is one of the relevant element in order to characterize the objective situation under scrutiny). – On the other side, situations conceived and performed in order to detect the presence of L, or to determine the amount or the value or the variation of L.

• In MC’s examples the specification of the CA1 of a linguistic item involves sometimes reference to some objective Eis (ex. Ei = com- bustions; L = ‘phlogiston’ or ‘oxygen’), and sometimes reference to some measuring Eis (ex. Ei = experiments with a balance; L = ‘mass’).

Thus, on the whole, to specify the CA1 of a linguistic item L in a theo- retical context T may mean: • Either to isolate objective empirical situations (whether naked- eye natural observations, naked-eye produced observations, or in- strumentally produced observations) for which the L-variable is thought, according to the adherents of T , to be relevant, if not ab- solutely required, in order to achieve a sound characterization (and situations for which, correlatively, the reality named L is thought — by the same scientists — to be indeed actually present).

I will label such cases ‘CA1obj’. In such cases the relation Ra underlying the verb ‘to apply1’ corre- sponds to the relation: ‘to be relevant’ (in order to achieve a sound characterization of the objective situation under study).

15The distinction corresponds more or less to the one introduced, in the present volume, by Emiliano Trizio when explaining his notion of dual taxonomies (that is, taxonomies composed by a part about experimental instrumented practices and another part about the objective reality under study). Reading his paper while writing my own has helped me to recognize the need to use a distinction of this kind in order to analyse MC’s notion of CA. 124 Léna Soler

• Or to isolate (most of the time instrumented) experimental proce- dures conceived as relevant reliable means to determine (most of the time to measure) L.

I will label such case ‘CA1mes’. Here the relation Ra underlying the CA1 corresponds to the re- lations: ‘to be relevant and reliable’ (in order to determine the magnitudes involved in some theory).

5.3. The dependance of the CA1 upon IR, CA1 in the en- larged/restricted sense

Remarks: CA CA A. Although there are most of the time links between 1obj and 1mes , it is not necessary that they coincide. We can imagine that (and find his- torical examples in which) two scientific traditions roughly agree about the relevance of the same empirical situations (about the fact that their theories have to explain such situations), but do not agree about (all) the experimental instrumented means that are reliable in order to determine the central variables involved in the available theories. CA This is a reason why it is better to distinguish carefully 1obj and CA CA 1mes , as two possible ways to understand the notion of 1. CA The term ‘ 1obj ’ refers to the set of the situations (possibly highly instrumented) to be explained (the relevant situations). It is the most intuitive and common way to understand the idea of ‘CA’ of a theory T L CA or a particular linguistic item . The term ‘ 1mes ’ refers to the experimental means supposed to be reliable with respect to the task of determining the magnibutes mentioned by available theories. Shifting from the specification of CA1 to the clause ‘to have the same CA1’ we have the following equivalences: CA Eis • Same 1obj = same set of relevant empirical situations . The adherents of two incommensurable theories agree about the objective empirical situations to be explained — or about most of them, most of the ones known by both rival traditions. CA • Same 1mes = same set of relevant reliable means for determining the scientific magnitudes involved. The adherents of two incommensurable theories agree about the reliability of the experimental procedures adopted to measure the- oretical variables — or about the reliability of most of them, of most of the ones known by both rival traditions. Incommensurability on the basis of a contextual theory of language 125

B. The descriptions of the empirical situations involved at both levels are of course, even in the case of naked-eye natural observations, all theory laden: all of them rely on a (in principle potentially evolutive) taxon- omy, be it a taxonomy covering naked-eye observations, or a taxonomy including instrument-types and experiment-types. This means that:

(a) The descriptions of what the historian of science sometimes identi- fies trans-paradigmatically as one and the same empirical situation, may be, in actual episodes of the history of science, coordinated to ‘observational’ descriptions that change from a scientific tradi- tion to an other incommensurable one. In that case the historian of science will be able to detect, by contrast, ‘tacit theoretical as- sumptions’ and ‘questionable inferences’ in the old scientists way of talking, where these old scientists themselves only saw ‘given observational descriptions’.

(b) Some (more or less hidden) IR are thus involved in the specifica- tion of CA1 (the one underlying the descriptions of the empirical situations involved), so that the specification of CA1 cannot avoid the specification of some IR. In other words, the CA1 determinant is not completely independent of the IR determinant.

(c) In consequence, we have to distinguish between two kinds of IR: the ones to be associated with the theoretical integration of a con- cept, and the ones to be associated with its empirical application. Yet this is indeed a problem, because the theoretical and empirical levels are of course not separated in re by a natural and sharp dividing line. We do not have, on the one side the description of the relevant empirical situations (with their underlying ‘observa- tional’ or ‘very empirical’ IR), and on the other side the theoretical descriptions (with their underlying ‘theoretical’ IR).

We will come back to points (b) and (c) section 6.

C. The situation is moreover complicated by the circumstance that the verb ‘to apply’ is currently employed in order to label epistemological configurations for which nobody assumes that the point of application Pa is ‘observational’ or even that it is a ‘faithful description of a real state of affairs’. We commonly say that a theoretical item L applies to this or that situation, where the situation involved is not, in any sense, an ‘immediately observational’ one, but is a highly theoretical and idealized 126 Léna Soler model supposed to cover an open class of empirical situations that may be perceptively very different16 from one another. D. And that is still not all. Suppose that difficulties B(c) and C are set aside, that is, suppose that Pa is unproblematically ‘observational’ or ‘very empirical’, and that we are indeed allowed, for some practical purpose, to draw a well determined dividing line between, on the one hand, the level of what can be taken as given (naked-eye or instrumented) observations Eis and, on the other hand, the level of what can be taken as theoretical interpretation of these Eis. This being admitted and according to our definition of CA1, to spec- ify the CA1 of L in the context of T should amount in principle:

(i) To describe a set of (by hypothesis unproblematically observa- tional) empirical situations Eis (let us label the network of IR constituting such descriptions IREi);

(ii) To select these Eis on the grounds that they are — among the larger set of the Eis that appear to be relevant with respect to the theory T to which L pertains — the Eis to which L applies. (If we CA L deal with 1obj , it means that the linguistic item is relevant and required in order to achieve a sound scientific characterization; CA Eis and if we deal with 1mes , it means that the mentioned are relevant reliable means in order to measure L).

In principle (i) and (ii) should be enough17, but in reality, this is rarely the case18. Why? Because it seems that more can (if not must) be said about the link Ra between L and the Eis. Saying that L is relevant for spelling out the Eis amounts apparently to stating nothing more than the fact that L indeed applies to the Eis.

16Kuhn’s texts offer many examples. Cf. for instance, in [Kuhn 1962], Kuhn’s analysis of the way the sketch-law F = ma ‘applies to nature’. Here, as in many other illustrations of the function of exemplars in science, ‘nature’ does not equate with ‘direct observations’ or even with ‘low-level theoretical statements’. ‘Nature’ means ‘highly theoretical idealized models of nature’, although less theoretical (i.e., here, less general) that the covering law F = ma. For further developments on this point, see Emiliano Trizio’s paper in the present volume. 17And sometimes things work in this way in MC’s presentation: for ex., when he claims that “phlogiston escape” and “oxygen bonding” have the same CA (CA1). Here the claim can be taken as implying that the phlogisticians and the lavoisians assume that roughly the same set of empirical situations are relevant (combustions, etc.), and that, in the presence of the same relevant phenomena, they will describe them, respectively as a phlogiston escape, or an oxygen bounding. 18Cf. the examples just below. Incommensurability on the basis of a contextual theory of language 127

But couldn’t L apply to the same Eis in many different ways? This is indeed a current way of talking. Think for example of the so-called em- pirically equivalent theories: they exactly embody such a configuration. This fact leads us to tell more about Ra: not only to state that L ap- plies to the Eis, but moreover to clarify how L is linked to them, to spell out in what precisely consists, in each case, the relation of application involved. Yet in order to do that, one has to introduce new demarcations within the total network of assumptions characterizing a given scientific tradi- tion. Suppose that one has taken the linguistic item L as the subject of the application Sa. L is not directly linked to the Eis, and L is not only linked to these Eis but also to many theoretical items. Thus in order to specify the CA1 of L one will have, given the Eis, to cut the whole inferential network surrounding L in two different parts: a theoretical IR ‘essential’ (or ‘defining’) fragment DL ; and a less theoretical fragment IRD Eis IR playing the role of bridge between the L and the ( B[L−Ei] ). In that case, the specification of the CA1 of L in the context T will require, besides the tasks (i) and (ii) mentioned above, the additional following task:

(iii) To spell out the way L is related to the Eis (and in so doing, to rely on a network of relations IRB ); or in other words, to spell out through what precise connexions the Eis are relevant with respect to the application of L, to spell out how L applies to these Eis.

Let us label a specification of the CA1 integrating this third compo- nent ‘the CA1 in the enlarged sense’ (contrasted with the CA1 in the restricted sense). To specify the CA1 of L in such enlarged sense implies, obviously, to enlarge the IR constitutive of CA1. Indeed, if we rely on the enlarged sense of the CA1, to accept the clause ‘L1 and L2 have the same CA1’ amounts to accept not only that the same Eis are relevant with respect to L1 and L2, but moreover that L1 and L2 are related to these Eis in the same way.

5.4. Applying the elaborated distinctions to MC’s analysis of examples

The preceding remarks will be developed in section 6 below. By listing them here, I mainly intend: first, to provide more fine-grained analytical tools in order to analyse MC’s examples and more generally examples 128 Léna Soler of incommensurability; second, to identify the reasons which — alto- gether or separately depending on the particular case under issue — work toward the undesirable effect that, in MC’s analysis of concrete examples, the two determinants of CA (CA1) and IR — that seemed at the beginning of his presentation, at the general and abstract level, well defined and separated — often interfere in practice. Let us give some illustrations. A. Here are some examples in which MC is claiming to deal with CA (my CA1) but in which IR surreptitiously enter into play, leading the reader to feel, at first sight at least, that the situation should be (or could be) characterized in terms of IR. Ex1. When MC gives the list of the celestial objects falling under the concept of “geocentric planet” (Moon, Mercury, etc.) as an exemplifica- tion of what it means to specify the CA of “geocentric planet”, we are at first sight surprised: in so doing, aren’t we typically spelling out the IR (or theoretical integration) of the considered concept? CA Now I would characterize the situation as a case of restricted 1obj : • Restricted, because the reasons why the Moon, Mercury etc. are assumed to be geocentric planets are not articulated (the way the linguistic item “geocentric planet” applies1 to the celestial bodies named “Moon”, “Mercury” etc. is not made explicit); • Objective, because the (descriptions of the) Eis here involved, that is, the (descriptions of the) considered celestial bodies as they ap- pear from the earth, may be viewed as (descriptions of) objec- tive given phenomena that astronomical theories have to explain, (rather than produced Eis identified with reliable means performed in order to show that the Moon, Mercury etc. indeed are geocentric planets).

Ex.2. MC claims that the CA (CA1) of “mass” in ED and SR are the same, because “mass is evaluated in the same way in the two ac- counts in question. They both endorse determining mass values using a balance or collision processes (thereby drawing on momentum conser- vation)” (84, emphasis added). Reading this passage we can see (since this is here explicitly pointed out by MC) that the empirical evaluations under consideration are not independent of something, namely the mo- mentum conservation, which is a highly theoretical principle holistically linked — according to the adopted contextual theory of meaning — to many other theoretical pieces, and which is then on the side of the IR (theoretical integration). Incommensurability on the basis of a contextual theory of language 129 CA Now, I would characterize the situation as a case of enlarged 1mes :

• Enlarged, because, with the allusion to the principle of momentum conservation, there is a (admittedly quite embryonic) specification of the way the linguistic item “mass” applies1 to empirical situa- tions involving balances or collision processes;

• Measuring, because the (description of the) Eis under scrutiny are, here, (descriptions of) basic instruments and basic manipulations corresponding to procedures intended to measure the magnitude named “mass”.

Ex3. When “impetus” and “momentum” are said to have the same CA (CA1) because “both quantities are estimated by the product of a body’s velocity and its weight or mass”, this sounds again at first sight strange: in specifying the relation between velocity and mass underlying the two incommensurable concepts, aren’t we typically deploying their theoreti- cal IR? In this example it is not easy to qualify the situations in terms of our distinctions, because it is not very clear if MC’s verb “estimated” intends to refer to measures of impetus and momentum via measurements of velocity and mass, or if it intends to refer to a theoretical explanation of the links assumed by both theories between the concepts involved. At least our distinctions allow us to identify promptly what we need to clarify in order to be able to specify the situation. By the way, the example illustrates how complex the situation is. Indeed, suppose that the first of the two possibilities listed holds19. Ad- mitting MC’s characterization, two different experimental measurements are required in order to determine each quantity (impetus and momen- tum), so that the linguistic item “momentum” (for ex.) applies1mes to two different Eimes — these Eimes corresponding to (the description of) the two basic experimental procedures. Now, these Eimes need to be related one to the other in a certain way if the momentum is to be determined. Yet, how are we going to characterise such a relation? If we want to equate the corresponding IR with a component of the specifica- tion of the CA1 of “momentum”, we can consider it as specifying the way “momentum” applies1 to the two Eis taken together. But this is a more complex case than the configuration considered above in (iii), in which the condition ‘the way a linguistic item L applies1’ named the relation

19This is probably what MC has in mind; if the second possibility held, I think we should better describe the situation in terms of ‘pure IR’ instead of CA. 130 Léna Soler between L and one single class of empirical situation Ei.

B. Here is, now, an example in which, reciprocally, MC claims to deal with IR, whereas we are at first sight inclined to qualify what is at issue as CA1. Just after saying that “phlogiston escape” and “oxygen bounding” have (roughly) the same CA (CA1), MC continues: “the drawback is that the inferential relations fail to be preserved. A case in point is that the presence of phlogiston is connected with the colour and the nature [oily-fatty nature for ex.] of the pertinent substance” [Carrier 2001, 76]. He goes on explaining that the adherents of the phlogiston theory see a substantial connexion between the presence of phlogiston on the one hand, and the colour and oily-fatty aspects of the bodies on the other, whereas such relation is no longer accepted by the adherents of the oxygen theory; he adds that phenomena like colour or oily-fatty aspect are no longer, for many lavoisians, relevant phenomena with respect to the task of a chemical theory. Yet, why does MC describe such a situation in terms of ‘different IR’? Aren’t we here typically in the presence of a case of ‘different CA1’? That is, a case in which each rival incommensurable theory assumes different sets of phenomena as relevant (here, very basic naked-eye observable phenomena like the colour or the fatty aspect of bodies)? Or else, if we consider those scientists that assume colour and oily-fatty nature to be relevant, aren’t we typically in the presence of a case in which the linguistic items under scrutiny differently apply1 to the same empirical situations?20. In brief, aren’t we typically in the presence of a case in which key concepts of each rival theory either apply to different sets of situations, or differently apply to the same restricted situations21? Personally I am inclined to subsume the present example under the CA CA category of 1obj , and to describe it as a case of difference of 1 (i.e. the two linguistic items under scrutiny, ‘phlogiston’ and ‘oxygen’, do not have the same CA1 for the empirical situations examined — ei- ther because they do not apply to the same Eis, or because they apply 20 The way ‘phlogiston’ applies1 — is linked by the phlogistician – to these Eis (for ex.: fatty-nature means a high quantity of a principle, phlogiston) is not the way in which ‘oxygen’ applies1 to the same Eis (lavoisians do not explain what this link is). 21 In the judgments concerning CA1, we can focus on a single restricted class of empirical situations, or enlarge the object of focus, up to a — of course idealized — clause corresponding to ‘all the phenomena that the theory has to explain’ or ‘all relevant phenomena’. This can of course modify the decisions about CA1 (the conclusion that we have the same or different CA1). The point will be examined in section 8 below. Incommensurability on the basis of a contextual theory of language 131 differently to the same Eis). The reason for this choice is that unprob- lematically very ‘observational’ ‘given’ observations are involved here (the colour of the bodies, their fatty aspect. . . ). Yet, as we will see in a more detailed way in section 7 below, such unproblematically intuitive observational character is one of the only way we have, in practice, to differentiate the CA1 from the ‘pure’ IR. If cases involving items that are so observational are not counted as CA, what will be? At least, we can experience, through the consideration of these exam- ples, how the application of the distinction between the two determinants CA and IR can be problematic in practice. I will come back later to this problem and try, in section 7, to identify at a more general level the fundamental reasons for such interferences between CA1 and IR. For the moment, let us keep in mind the central conclusion: we cannot avoid to rely on some IR in order to specify the CA1 of any scientific linguistic item.

6. Exploring the substantial relations between CA1 and CA2

Let us now come back, as promised at the end of section 4, to the sub- stantial common points and relations between CA1 and CA2, the ones that may justify the appeal to a common generic expression in order to label the two operations involved. As already noticed in section 4, in current usages we employ one and the same verb ‘to apply’ to mean CA2 in some occurrences, and to mean CA1 in some others. Yet, this fact is not at all gratuitous. Indeed, CA1 and CA2 are two distinct but related senses, and it is not useless, for the analysis of our present problem, to clarify the nature of these relations. The fundamental common point between CA1 and CA2 is obvious: both concern the relation between the linguistic and the non linguistic, the connection between the words and the world. The differences come from the sort of relation involved. This last point has been already sketched in section 4, but it can now be restated relying on the analysis of CA1 provided in section 5.

A. ‘The relation of L to the physical world’, understood in the CA1-sense, names:

• either (if we consider the restricted CA1) simply a no further spec- CA CA ified relation of relevance (for 1obj ) or of reliability (for 2); 132 Léna Soler

• or (if we consider the enlarged CA1) some specified connexions (my IRB) that a given scientific theory T assumes between L and some observational situations Eis taken as given.

At this level, two remarks can be done. First, a physical (or more generally scientific) concept will always have CA in this sense. Indeed, a physical concept cannot completely fail 22 to apply1 ; otherwise it would reduce to a purely metaphysical concept (in the logical positivist sense). Second, to recognize that an expression applies1, and eventually to spell out moreover some of the precise relations IRB that are responsible for this application in a given framework T , is in principle completely independent of any ontological presupposition or commitment about the real/fictitious character of the theoretical states of affairs involved. Once the links between L and some empirical situations according to T have been stated (for ex. once explained that — or in what way — the words ‘phlogiston’ or ‘oxygen’ are related — apply1 — to experiences of combustion in their original framework), we still have to decide if these relations are sufficiently adequate, objective or true of the world. It is at this point that CA2 eventually come into play, as higher- level judgments about lower level relations (the later lower-level relation being possibly relations involved in the specification of CA1 — in my notations, IRB).

B. The relation of L to the physical world’, understood in the in the CA2-sense, names, as we explained section 4, a modal judgment (a judgment of sufficient empirical adequacy or of independent existence) about some previously specified first level assumptions. Now, the object of such modal judgment, that is, the previously specified first level assumptions can, in principle, be identified with any selected part of the T -framework:

• with some IRB; IR • or with some DL .

Hence, as a particular case, the object of such modal judgment can be something previously characterized under the category of ‘CA1’. In such cases, previously specified CA1 are a required condition of the possibility

22Even if the connections of this concept to empirical situations are complex and indirect. I will come back to this point below. Incommensurability on the basis of a contextual theory of language 133 of CA2-judgments, and there is a generative link between judgments of CA1 and judgments of CA2. This is especially striking if we understand CA1 in the enlarged sense, that is, if we include in CA1 of L some spec- ification of the way L is linked to the relevant empirical situations Eis. In that case, determined CA2-judgments depend on the number and on the success of the (often predictive) bridge statements that constitute the CA1’s network and that link L to observational/experimental situa- tions. CA2-judgments (= ‘the linguistic item L, understood according to theoretical context T , applies2, or fails to apply2’) are therefore largely rooted in (if not univocally determined on the basis of) an evaluation of the way L applies1 (or fails to apply1). For our purpose, the point is better considered in a comparative per- spective: the verdicts ‘L2 of T2 applies2 / L1 of T1 fails to apply2’ are largely grounded in a comparative analysis of the way L1 and L2 respec- tively apply1 (or fail to apply1) within their original (different, eventually incommensurable) frameworks T1 and T2. True, on the whole, the bal- ance is not always easy to make, and in real historical situations, it is not necessarily consensual. The more the theoretical change is revolutionary, the more incommensurability will increase, and the more the judgments about the empirical global superiority of one theory on the other will become increasingly delicate, and possibly, in actual revolutionary peri- ods, not homogeneous in the community of specialists23. Nevertheless, from the overhanging perspective of the historian of science, there is no doubt that einsteinian relativity is empirically superior to Newtonian physics, or that the oxygen theory is, by far, more empirically adequate than the phlogiston theory. This is true in the minimal sense that the post-revolutionary theory is largely more apt, on the whole, to account for (that is: to apply1 to) known empirical situations (and this, despite of some possible marginal cases of kuhnian losses). Admittedly, in actual historical controversies, other factors than quan- titative considerations concerning the set of empirical situation explained come into play in theory comparison (such as estimations of simplicity, or conformity to other aesthetical or thematic requirements. . . ). But considering the net result of the historical process, we can claim that the recent theory T2 is indeed supported by a larger number of empirical situations than T1, and that T2 is able to predict more exactly some em- pirical situations also predicted by T1: in other words, T2 applies1 better than its rival T1. Yet from this fact, one commonly tends to conclude that T2 is a better description of reality than T1, which is equivalent

23Cf. [Soler 2004a]. 134 Léna Soler to say, in our technical vocabulary, that T2 applies2 whereas T1 fails to apply2 — or more cautiously: that if one of the two theories T1 and T2 refers to real states of affairs (= applies2), it has to be T2 and not T1. In brief, the judgments about the success/failure of the associations assumed, inside of each rival framework T1 and T2, between L and some observable experimental results (i.e. the judgments about the quality of CA1), indeed influence deeply the modal comparative judgments about the comparative adequacy of each theory (i.e. the judgments about the 24 ability/failure to apply2). In most cases , at least from the point of view of the historian, it is because L2 is thought to apply1 better than it’s correlate L1 of T1, that L2 is assumed to apply2 whereas its correlate L1 of T1 is assumed to fail to apply2. On the basis of these considerations, developed with the intention to clarify the relations between CA1 and CA2, I want to reaffirm a previous conclusion and make a remark. At the end of section 4, I concluded that, although CA1 and CA2 correspond to different operations that have to be distinguished in the context of the incommensurability problem, it is legitimate to use one and the same generic expression to label both operations. I maintain that conclusion and hope that the arguments in its favour are now clear. The remark is the following. As noticed above, first we need, in order to perform modal judgments corresponding to CA2, to specify and to take for given some aspects of the theories T1 and T2 under scrutiny, and second, modal judgments of the application2-type can in principle be directed toward any part of the T -framework. In particular, the later judgments can be directed either toward highly large networks of assumptions held by the adherents of T , or toward very circumscribed propositions (for ex. toward the following one — say (p) –, ascribed to a phlogiston world-view’s adherent: ‘one and the same substance is exchanged in all reactions of combustion’). Yet, it is important to stress the interdependence between, on the one hand, the choice to focus on this or that (more or less extended, more or less observational) network of relations surrounding a given term L in a given context, and on the other hand, the judgments in favour or

24In most cases only, for two reasons: first this holds on the whole, concerning several important concepts of the theories under comparison, but it could fail to hold for some particular marginal concepts; and second, we can imagine some peculiar situations, for example periods during which a new theory is proposed, in which some practitioners of physics believe that this theory is the good one (i.e. that this theory is the most accurate as to its fundamental ontological assumptions), even if it has not yet proved its empirical superiority with respect to the existing alternatives. Incommensurability on the basis of a contextual theory of language 135 against the conclusion that a term applies2. In MC’s second try, the modal judgments involved in the examples are most of the time directed toward broad networks of theoretical rela- tions — eventually including our statement (p) but in association with many other theoretical claims about phlogiston that the oxygen-theory T2 rejects. On the basis of this choice, MC is led to conclude, at the end of his second try, that the linguistic item ‘phlogiston’ under scrutiny fails to apply2. Now, if one had chosen to focus on more restricted parts of the phlogiston theory involving the same linguistic item ‘phlogiston’ (for ex., if one has focussed on our (p) in isolation), the conclusion relative to the possibility for the term to apply2 would have been the opposite, since (p) is maintained by T2. This remark, and many other previous ones concerning the necessity to cut within the whole network of assumptions constituting a scientific paradigm, points to a cluster of important difficulties that we will discuss in the next section.

7. Some intrinsic difficulties of the holistic-contextual framework

Many of these difficulties do not concern specifically MC’s approach and arise inevitably in any approach committed to the holistic-contextual framework. They represent therefore difficulties that are essentially con- stitutive of the incommensurability problem for anyone who thinks, like so many people today, including me, that the holistic-contextual frame- work is not a free methodological choice but a deep feature of human scientific practices. However, they remain relatively hidden in MC’s presentation, and sometimes take a particular form in MC’s model of translation, which I will try to make explicit in the course of the reflec- tion. Globally considered, the difficulties referred to have, I think, two sources.

• What I will call the global/local dilemma: the problem that al- though we recognize that our scientific theories work holistically (that our concepts are systems of correlated concepts, some of them possibly equated with observational ones), we also have to consider them in isolation and cannot use them without, up to a point, disconnecting them from the whole linguistic structure and from the whole set of empirical situations to which they owe their meaning. 136 Léna Soler

• What I will call the theory/observation dilemma: the problem of reconciling the today well-known fact that there is no sharp demar- cation line between the observable and the theoretical levels (this is the famous thesis of the theory-ladeness of any observation), with the epistemological necessity to maintain the distinction, to admit, at a pragmatical level and in a given historical context, that certain areas of our linguistic systems can be considered as direct descriptions of empirical basic states of affairs.

We need fundamental distinctions of these types. But at the same time, we have to recognize that such distinctions are pragmatical and most of the time not very sharp. This poses special difficulties when we try to compare two deeply different frameworks.

7.1. Indeterminations at the level of judgments concerning IR

Consider, first, judgments about IR. In order to characterize incom- mensurability precisely, we have to discuss as carefully as possible if (and why) two given linguistic items either have sufficiently similar IR (so as to be said translatable according to the clause ‘same IR’), or have too different IR (so that they must be considered as untranslatable ac- cording to the clause ‘same IR’). In the framework of a contextual holistic theory of meaning and in the light of the global/local dilemma, we can anticipate that many diffi- culties will hinder such discussions, and we can understand their cause. A holistic theory holds that the use of a term is determined by its rela- tions to other words and to empirical situations. If holism is drastically global, each linguistic item will have to be determined with reference to the totality of its original framework: that is, each linguistic item L will, in a way, contain the whole theory T , where T includes all the con- nections to empirical situations that hold for an adherent of T . Under such assumption, the only situation in which it would be impossible to conclude that L1 of T1 and L2 of T2 have the same IR, would be the case in which T1 = T2, and the criteria of IR would be deprived of any operativity. Yet, as previously noticed, for epistemological and practi- cal reasons, holism cannot be drastically global: we must assume local holism. The consequence is that we have to cut the linguistic system into parts. And the problem is to decide where the cut is to be made. With respect to the task of comparing rival concepts L1/L2 involved in rival theories T1/T2, we have to decide, considering the whole frame- works 1 and 2, which part of the integral inferential network associated Incommensurability on the basis of a contextual theory of language 137 to L1 in T1, and which part of the integral inferential network associ- ated to L2 in T2, are really important/anecdotic, essential/secondary, considering the aim that is being pursued. We encounter here a new version of a traditional philosophical problem, namely that of the essen- tial/secondary properties. Yet this kind of decision is far from being trivial, since nothing im- poses one unique and consensually evident cut: there is, at this level, a fundamental indeterminacy. And the more the theories are incommensu- rable, the more the decisions of different subjects will be heterogeneous [Soler 2004a]. In MC’s presentation this difficulty is hidden, relegated in the back- ground: although what constitutes the ground for the judgments ‘same IR’ or ‘different IR’ is clearly specified or identifiable, the reasons for underlying cuts, and a fortiori the very fact that these judgments need to rely on a non trivial cut, are not explicit. Yet the indeterminacy becomes palpable to the reader, in cases where he would have himself cut differently and thus would have come to different conclusions about sameness/differences of the IR associated to two linguistic items. The above considerations about statement (p) ‘there is one and the same substance exchanged in all reactions of combustion’ can provide an illustration in principle. If we operate a very circumscribed cut within the inferential networks surrounding ‘phlogiston’ in T1 and ‘oxygen’ in T2 — for example if we extract the particular statement (p) and focus on it only —, we will conclude that L1 and L2 have the same IR. But if we enlarge the inferential network associated with L1 and L2, the conclusion will be the opposite. The case will maybe not appear very convincing, because of the com- mon intuition that ‘phlogiston’ cannot be essentially reduced to the (p) characterization. But take the much discussed case of ‘mass’ in Newto- nian and Einsteinian physics. Here the intuitions of the speakers are not so uniform. Some are ready to grant that a sufficient core of Newtonian assumptions about mass are conserved in Einsteinian special relativity, so that we can conclude that ‘Newtonian mass’ indeed refers, or in our vocabulary applies2. But others do not agree at all with this analysis and believe that it is illegitimate to separate the shared and unshared assumptions of Newtonian and Einsteinian scientists about mass, and thus tend to conclude that Newtonian mass fails to apply2. We can also appeal to the example of mass analysed in MC’s paper (section 4). The very fact that “the dependence of total mass on real mass and velocity is mathematically identical to the dependence of relativistic 138 Léna Soler mass on rest mass and velocity” could be taken as a sound argument in favour of the conclusion — which is not MC’s one — that “total mass” and “relativistic mass” indeed (roughly) satisfy the criteria ‘sameness of IR’. The adjective ‘roughly’ is here crucial. But since the criteria are never exactly satisfied, we face a real problem in cases where intuitions of the speakers do not coincide.

7.2. The ‘observational status’, as the central discriminative pragmatical criteria in order to distinguish CA1 and IR in prac- tice

The previous difficulty overlaps with another one, already briefly intro- duced section 5, related to the fact that the distinction between CA and IR is not so sharp, or more exactly, that the CA1 criterion is not independent of the IR criterion (and hence inherits all the difficulties pertaining to the latter). Indeed, to specify the CA of a term can not be done without specifying some of its IR in a given framework. Let us recall briefly why and explain the point a little bit more.

A. What does the philosopher of science have to do, when asked to specify the CA1 of a given linguistic item L in the theoretical context T ? In the restricted sense of CA1, he has to specify:

(i) The relevant empirical situation(s) Eis to which the linguistic item L is assumed to be applied according to the adherents of T ;

In the enlarged sense he has moreover to specify the way L applies to each Ei, that is:

(ii) Some relations holding between L and each relevant empirical sit- uation Ei according to the adherents of T .

The first element (i) points to a non linguistic, empirically given com- ponent, and it is precisely what leads one to talk about ‘CA’ instead of ‘pure IR’. So it is clear from the beginning that the very difference between the two constraints upon translation, CA1 and IR, will at the end have to be located around this point. But this being said, a network of IR underlie both components (i) and (ii). Incommensurability on the basis of a contextual theory of language 139

This is explicit in the very definition of (ii): to specify the CA1 in the enlarged sense inevitably implies to spell out some inferential relations, labelled IRB section 5. And this holds too for (i), although maybe less obviously (cf. section 5, B). Indeed, the empirical situation E1 (resp. E2, E3, ..., Ei) targeted in (i) is never — at least from an overhanging historical perspective — a single situation that could be identified here and now by ostension. It is a constituted (in principle infinite) class of situations assumed to be of the same kind. To identify and circum- scribe this kind of situation, the philosopher of science has to rely on a description of it, formulated in a specific language associated with a specific taxonomy. Even if such a description may be labelled ‘obser- vational’ and considered, at a given developmental stage of knowledge, as a sort of ineluctable double of a piece of observation — so that we can say, in an intuitive and pragmatic sense, that the specification of CA1 have to include observational linguistic items –, it remains, just as every description, questionable in principle (as questionable as the ‘theoretical’ assumptions that constitute it) and deconstructible. Hence, strictly speaking, to specify the (i)-component of CA1 amounts, from the perspective of the historian of science, to rely on a (‘observational’ or ‘empirically given’) network of IR (labelled IREi section 5).

B. But then the question arises: which inferential relations? If the CA1 includes some IR, which part of the total inferential relations of an item L have to be counted as pertaining to its CA1, and which part have correlatively to be counted as ‘pure IR’? The ‘grammar’ (in a wittgensteinian sense) of the verb ‘to apply’ requires an artificial separation between at least two but more often three different parts corresponding to two or three fragments of taxonomies and levels of descriptions25: For the CA1 in the restricted sense we have:

• A (relatively) higher level (or more theoretical, general level), in- timately linked with the subject of the application L, in which an IR DL is selected; • A (relatively) lower level (or less theoretical, more particular level),

25In doing this we go back to a formulation of epistemological problems that is structurally very close to the one that the logical positivists assumed, the main dif- ference being that in the framework of the contextual-holistic theory of meaning all distinguishing determinants (observational/theoretical, etc.) are assumed to be pragmatically and contextually determined features, rather than absolute properties of the states of affairs. 140 Léna Soler

intimately linked with the point of application, within which some Eis are selected, and to which L is said to apply.

For the CA1 in the enlarged sense we have moreover:

• A (relatively) intermediate level, within which some IRB are se- L IR lected and by the medium of which (that is, DL ) is connected to the Eis.

Now, what tells us how to cut within the total inferential network at the heart of which L lies, so as to isolate the IR (IREi and IRB) contributing to the CA1 of L? The demarcation line between the DL- and the B-levels is neither sharper nor more objective than the one between the observational and the theoretical, or between the lower level and the two other ones. Moreover, the situation is complicated, as already noticed section 5.3. C, by the fact that the point of application of the verb ‘to apply’ is not, in current usages, restricted to unproblematic ‘direct observations’, but commonly includes highly theoretical and idealized models. We saw that the ‘grammar’ of the verb ‘to apply’ requires an artificial separation between two or three networks of IR corresponding to three levels of descriptions positioned on a scale of ‘theoreticity’. Yet, this does not imply the assumption that the lower level is observational in the common intuitive sense. And there are many current usages of the verb ‘to apply’ that presuppose the contrary (see the example note 16). However, leaving the reference to current usages and focusing on the task to make the CA1 and IR determinants as operant as possible in the practice of the philosopher, I think we should try to avoid to sub- sume under the CA1 category configurations in which the Eis involved coincide with too theoretical idealized models. In other words, I am inclined to consider the ‘observational’ status of the Eis as the central discriminative pragmatical criteria when having to choose between a characterization in terms of CA1 and a characterization in terms of IR. Of course, there is, once more, no absolute demarcation involved here, and we have to rely on intuition. However, one thing has to be stressed: from the viewpoint of the historian of science comparing two incommensurable paradigms from the vintage point of the overhanging perspective, the ‘given-observational’ status can be legitimately ascribed only to statements or assumptions that have indeed been (or would have been according of the historian) unproblematically taken as ‘observa- tional’ by the adherents of both incommensurable traditions. In this Incommensurability on the basis of a contextual theory of language 141 way we can give a sense to the clauses ‘T1 and T2 have the same Eis’, 26 ‘T1 and T2 target a common set of relevant Eis’ . Let us recapitulate. We are left, when wanting to use the CA1 and IR determinants, with the necessity to cut within the inferential net- work involving L in order to extract the CA1 of L, together with the difficulty that nothing imposes a sharp dividing line between what has to be counted as pertaining to the CA1’s network of L, and what has to be counted as pertaining to the theoretical integration network of L. Ambiguities may arise, and in fact do arise, in the analysis of histor- ical case studies. We sometimes hesitate to characterize the situation in terms of CA1 or in terms of IR, to conclude that we have a case of ‘same- ness/difference of CA1’ or a case of ‘sameness/difference of IR’, and we are sometimes astonished by the characterizations given by others (cf. as an illustration the discussion of MC’s examples at the end of section 5). Even when no ambiguity arises in practice — when everybody is intuitively inclined to uphold the same conclusions about CA1 and IR –, I think it is important to make explicit that the two characteristics CA1 and IR are not mutually independent characteristics.

7.3. Coming back to the analytical characterization of the dif- ferences between CA1 and IR

I tried to clarify the relations of CA1 and IR and to analyse the rea- sons of the difficulties related to the demarcation. But now, I want to repeat that from an epistemological point of view, the distinction be- tween CA and IR seems to me as required as the distinction between the observational and the theoretical –, although no less problematic. It is therefore worth restating in what the difference between CA1 and IR consists, in principle at the analytical level, independently of the possible ambiguities related to the application of the distinction.

• To specify the ‘IR of L’ requires to extract, within the whole lin- guistic network involving L in a given historical context, a single unitary fragment encapsulating only theoretical linguistic items, covering only inter-conceptual links detached from any connexion to anything playing the role of ‘direct observation’.

• Whereas to specify the ‘CA1 of L’ requires moreover, in the re- stricted sense to extract the IREi corresponding to the lowest ‘ob- servational’ linguistic level, and in the enlarged sense, to clarify in

26See [Soler 2003]. 142 Léna Soler

IRB addition the [L−Ei] corresponding to the intermediate linguistic level.

Hence, from an analytical perspective, the difference between the two operations ‘to specify the IR’ and ‘to specify the CA1’ lies in two facts. • There is in the second case, but not in the first, a division of the whole linguistic network encapsulating the whole system of beliefs of scientists in several areas understood as hierarchical levels. • The lowest level encapsulates descriptions targeting taken-for-given perceptual situations, and the highest one encapsulates theoretical descriptions targeting unobservable states of affairs whose exis- tence is supposed to account for the known experimental results. Thus we find in the second case, but not in the first, some ‘ob- servational’ linguistic items (at least as targeted, sometimes in an indirect way), or some linguistic items having the same function in a given context (that is, being in this context unproblematically taken-for-granted descriptions of empirical situations). All this encourages us to prefer, when having to name the ‘pure IR’ of a linguistic item L (by contrast with the IR involved in the CA1 of L), the systematic use of the expression ‘theoretical integration of L’ (often employed by MC as an alternative to ‘IR’), instead of the more generic one ‘IR’. The former label has the advantage to underline that it is a peculiar kind of IR that is involved in the case of ‘pure IR’: namely, a network that can be negatively characterized as exempt from any observational linguistic item. However, the label does not have to be understood as signifying that the IR involved in the specification of the CA1 of L are, by contrast, not theoretical and have nothing to do with theoretical integration. Indeed, it is worth repeating that although the IR involved in the specification of the CA1 of L target observations and thus inevitably comprise some observational linguistic items, they cannot themselves be seen as ‘purely’ observational. The corresponding network will, inevitably, contain theo- retical terms. Indeed, if L is a high-level theoretical terms of T , it will be impossible to specify its relations to empirical situations Eis (the way it applies1) without using, in addition of L, some other very theoretical signifiers L′,L′′ . . . In Kuhn’s words, theories involve interrelated terms that work holistically and apply together to nature. We encounter here the indeed delicate but inescapable problem of evaluating the “empirical import” [Carrier 2002, 134] of a single concept in the framework of a contextual-holistic account of language. Incommensurability on the basis of a contextual theory of language 143 8. Some additional reflections about comparative judg- ments involving CA1

Let us consider now comparative judgements involving CA1. Such judgments have to estimate the similarities/differences between the CA1 of two linguistic items L1 and L2, in order to conclude that L1 and L2 possess the same/different CA1. Yet, it follows from the preceding analysis that to compare the CA1 of two linguistic items L1 and L2 means to contrast each of the two elements (i) and (ii) specified section 7:

• on the one hand the empirical situations Eis to which each of our items apply;

IRB • and on the other hand, the network of relations [L−Ei] spelling out the way each of them apply to its Eis (with the limiting case where IRB = the simple claim that L1 and L2 indeed apply to their Eis with no further specification as to the ‘how’).

This being admitted, there are, at the most general level, four possible combinations: L1 and L2 may be:

IR IR (a) Similarly related to the same empirical situations; ( B1 = B2 = IRB) and (Eis1 = Eis2 = Eis); IR IR (b) Differently related to the same empirical situations; ( B1 6= B2 ) and (Eis1 = Eis2 = Eis); IR IR (c) Similarly related to different empirical situations; ( B1 = B2 = IRB ) and (Eis1 6= Eis2); IR IR (d) Differently related to different empirical situations; ( B1 6= B2 ) and (Eis1 6= Eis2).

In the limiting case (= for CA1 in the restricted sense), the verdicts of the type ‘similarly/differently related to. . . ’ reduce to a disagreement concerning the relevance of a given class of Eis with respect to a given linguistic item L (for ex., if Ei = the fact of coloured bodies, T1 = the phlogiston theory and T2 = the oxygen theory, we can say that T1 and T2 are differently linked, in this minimal sense, to the same empirical situation Ei). 144 Léna Soler

Outside of the limiting case, the difficulties of the verdicts of the type ‘similarly/differently related to. . . ’ have already been discussed. They are difficulties inherent to judgments about sameness/differences of IR, generated by the necessity to make cuts within each of the whole linguistic structure involving respectively L1 and L2, joined to the fact that nothing imposes this or that element as constitutive/secondary and that the choice to focus on certain units instead of others may lead to antagonist verdicts (cf. sections 5 and 7). It remains now, first to consider the clause ‘same/different empirical situations’; and second, to analyse the relation between each of the four cases (a) to (d) on the one hand, and global verdicts of ‘same/different CA1’ on the other hand.

8.1. Comparative judgments involving the CA1, discussed in reference to a circumscribed kind of empirical situation

With respect to the first point, it is important to stress, as MC rightly points out, that in comparing two rival incommensurable theories, it will always be possible to identify some empirical situations for which both T1 and T2 claim responsibility (situations that both the adherents of T1 and T2 think they have to explain). In other words, there will always be some L1 of T1 and L2 of T2 that will apply to the same empirical situations (in the minimal sense of being relevant in order to describe such common Eis).

Such identical empirical situations jointly targeted by T1 and T2 may be described, at least by an historian of science having the advantage of an overhanging perspective and mastering both T1 and T2, by means of a unique ‘observational’ description. Of course such a description would not be completely theoretically neutral. It would be neutral only with respect to both T1 and T2. In other words it would be a description that is sufficiently independent of the divergent assumptions of T1 and T2. (Such a description is not nec- essarily a statement that has been actually used by the real practitioners of science associated with the two studied incommensurable traditions. It may well be a statement formulated in a meta-language especially elaborated by the historian for the purpose, a statement that has never been actually used by scientists but that is nevertheless imputed to them in the name of the assumption that they would have accepted it) 27.

27I elaborated a similar thesis in [Soler 2003]. Incommensurability on the basis of a contextual theory of language 145

Thus there will always be some pairs of L1-L2, about which it is possible to say that they are linked to the same empirical situation picked out by one single actually available observational common description (like ‘situations of combustion’, ‘movements relative to specified concrete frames of reference’, etc.). At first sight this seems to be a necessary condition to conclude that L1 and L2 do have the same CA1 (with respect to a specified class of empirical situations). However, the possibility of case (c) incites us to examine this conclusion a little bit more. Indeed, case (c) could correspond:

• Either to an extension to newly discovered phenomena of an al- ready available explanatory scheme (an extension of the domain of application of the theory, as one commonly says); • Or to a displacement of an already available explanatory scheme on phenomena already known, but to which the sketch in question was not applied until now, and to which other (possibly incompatible) explanations were previously applied.

Given the flexibility and the polysemy of the verb ‘to apply’, we could be tempted to say, without going against current usages, that in such a case, L1 and L2 do have the same CA1 (=similarly apply1), although the requirement ‘to be linked to the same empirical situation’, that seemed at first sight to be a pre-condition of the verdict ‘same CA1’, is not fulfilled (L1 and L2 are here linked to different specified empirical situations). However, my position is that case (c) is better described under the label ‘different CA1’. This is because of the fact, already emphasized, that if we want to be able to maintain a distinction between CA and IR despite of the circumstance that to specify the CA1 of L requires to specify some IR of L, then, we have to confer a primary role to the factual (extra-linguistic, empirical, non-inferential) component targeted in the CA1’s clause (primary compared with the IR component). Thus in cases in which L2 is related to empirical situations E2s unknown or unexplained by T1, and related to these E2 in the same way that L1 is already related to other empirical situations E1, it seems better to say:

• On the negative side, that L1 and L2 do not have the same CA1 (with respect to the restricted class of the E2s. It of course remains, on the basis of the multiplicity of such local verdicts, to enounce a global judgment covering the whole body of the empirical situations relevant for the adherents of T1 and T2, cf. below). 146 Léna Soler

• And on the positive side, that L1 and L2 do have similar IR but different CA1 with respect to the E2s.

Let us admit that the requirement ‘to be related to the same kind of empirical situation’ is a necessary condition to the judgment ‘to have the same CA1’. It is, however, of course not a sufficient one. Otherwise we would have to say that all concepts related in one or in an other respect to a given isolated empirical situation have the same conditions of appli- cation! (for ex., mass and length in the Michelson-Morley experiment28). We need more than this, because L1 and L2 could be related to the same empirical situations in very different ways (=situation (b)). We need, furthermore, that L1 and L2 be related to the same empirical situation in a sufficient similar way — and here we are back to the problem to decide when we are ready to consider that the two underlying networks of IR as ‘sufficiently similar’. On the whole and at a general level I conclude, concerning the rela- tions between the verdicts of the ‘same/different CA1’-type on the one hand, and cases (a) to (d) on the other hand, that: For two linguistic items L1 and L2:

• Cases (a) and (d) obviously correspond, respectively, to judgments of ‘same CA1’ and ‘different CA1’; • And cases (b) and (c), at first sight less obvious, are finally better described as two cases of ‘different CA1’.

8.2. Comparative judgments involving the CA1, discussed in reference to ‘the whole set of relevant empirical situations’

All this holds in reference to a circumscribed kind of empirical situation. But let us now consider the judgments of CA1 in reference to the whole set of the empirical situations that the adherents of T1 and the adherents of T2 consider to be scientifically relevant. The relation between the set associated with T1 and the set associated with T2 is rarely (and probably never for incommensurable theories) a relation of strict inclusion, let alone one of an identity. There are, in most

28Note that it is precisely in order to avoid such an absurd way of describing the epistemological situation, that one cannot reduce the relation of application consti- tutive of CA1 simply to a relation of relevance without any further specifications, and that one is correlatively almost inescapably inclined, in the analysis of concrete cases, to understand the CA1-clause in the enlarged sense, namely, to specify, up to a point, how L is related to the relevant Eis according to T . Incommensurability on the basis of a contextual theory of language 147 cases, empirical situations Eis to which one of the two incommensurable theories is related but not the other (where the ‘is related’ may mean either ‘actually explains’ or ‘has in principle to explain but is not yet able to do it’). Let us develop briefly the point.

It seems obvious if we take the later theory T2 as the frame of refer- ence. Indeed, nobody denies that T2 possesses, at least when considered on the whole and a long time after its victory on its rival T1, a broader scope than the earlier theory T1. The theory T2 accounts for empirical situations and experiences that were either unexplained or even com- pletely unknown at the time T1 was holding sway. Yet, although less immediately obvious, the point holds too, at least locally, if we take T1 as the frame of reference. It corresponds to what is nowadays commonly referred to as ‘kuhnian losses’: phenomena for which T1 claims responsibility (and eventually, phenomena that T1 was believed to explain well), but that the adherents of T2 consider with- out any relevance (for instance: the colour and the oily-fatty nature of bodies, with T1 = the phlogiston theory and T2 = the oxygen theory).

If we focus on a particular kind of empirical situation to which L1 of T1 is linked but no L2 of T2 is linked (for ex.: the coloured aspect of the bodies), we will of course conclude that L1 and L2 do not have the same CA1. However, judgments of ‘same/different CA1’ are not in general referred to a single circumscribed class of empirical situations of the same kind (for example, combustions/coloured aspect of the bodies). They are, most of the time, global judgments corresponding to a balance based on a large set of different kind of experiences and observations (combustions, coloured aspect of the body, plus many other kinds of experiences for which either T1 and T2 claims responsibility, or only T2, or only T1). This introduced a sort of second order difficulty (the first order one corresponds to the previously analysed ambiguities of the judgments based on a restricted specified class of empirical situations). Judgments that L1 and L2 do have (resp. do not have) ‘the same CA1’ rely on an evaluation of their being grounded on a sufficiently important common empirical basis (resp. in a too narrow common empirical basis). Yet, the balance may be delicate, especially for incommensurable theories. One will of course not be ready to conclude that L1 and L2 have similar conditions of application, on the grounds that L1 and L2 have the same CA1 for a given specifiable restricted class of empirical situations, if the class in question is too poor (is reduced to a few empirical situations, 148 Léna Soler or to empirical situations considered by both T1 and T2 as anecdotic or of secondary importance). But once again, such evaluations engage an intuitive and inevitably pragmatic component. As a result, their conclusions are often not consensual, and the arguments underlying them not uniformly convincing.

Conclusion

MC’s central characterization of incommensurability corresponds to the following thesis. Kuhn has been right, in his last work, to identify in- commensurability with untranslatability. Yet such identification needs to be clarified, and this can be done in the framework of the contextual theory of meaning. Incommensurable concepts appear then to be de- fined as concepts translatable with respect to only one or the other, but never to one and the other, of the two conditions that must be satisfied in order to obtain a good translation, namely, ‘same CA’ and ‘same IR’. However, I conclude from the above reflections that MC’s thesis can- not, unfortunately, be maintained as such. I say ‘unfortunately’, because the symmetry of MC’s thesis was indeed attractive. But this symmetry actually lies on a too flexible and permissive usage of the expressions ‘conditions of application’ and ‘preservation of the inferential relations’. Once having distinguished the CA1 from the CA2, and once having examined what should be a proper translation according to inferential relations (= a T IR), this nice symmetry does not resist, and we feel the need for more fine-grained distinctions in order to grasp the complex and diverse situations under study. I have tried to suggest some solutions in this direction, but a lot of work remains to be done. In the framework of a holistic and contextual account of the scientific activity, and under the assumption that there is nothing that can be identified with certainty to absolute and irrefutable data independent of any way of talking, I think we — historians and philosophers of science — have to begin with what we have, that is, with inferential relations underlying statements assumed by each of the scientific traditions under study. In other words, the IR determinant is, from the methodological point of view, of primary importance relatively to the CA (my CA1) determinant. It is only once having exhibited the two inferential structures (and the two coordinated taxonomies) associ- ated with each of the two compared theories T1 and T2, that one can begin to ascribe to certain structural fragments the status of being ‘ob- servational’ or ‘protocolar’, that one can then characterize the situations either in terms of CA (CA1) or in terms of ‘pure IR’, and that one can Incommensurability on the basis of a contextual theory of language 149 ask questions about the preservation of such determinants for key terms — with all the difficulties and ambiguities emphasized above. This being admitted, I think that Kuhn’s characterization of (se- mantic) incommensurability is the good one and the most fundamen- tal one: incommensurability names the relation between structures and taxonomies that are not superimposable and that are for this reason not mutually translatable. If we want to go further, relying on the CA1 and IR determinants, it seems that something like the following holds:

• Incommensurable concepts are never translatable according to the criteria ‘sameness of IR’ (are never T IR) — and here is the main point of disagreement between MC and me, at least at the level of general formulations29. The incommensurable concepts are the ones corresponding to two (on the whole) very different networks of inferential relations, and as a result, the ones that possess no good correlate in the rival theory according to the criteria ‘(on the whole) sufficiently similar IR’.

• As a consequence, incommensurable concepts cannot both apply2 (since they point to incompatible realities).

• However, incommensurable concepts must have some non negligi- ble fragments of IR in common (otherwise they would not appear

29I say ‘at the level of general formulation’, in the sense that it is only consid- ering nominal formulations that we find two contradictory claims (my claim that a translation preserving the IR (=my T IR) is always impossible / MC’s claims that a translation preserving the IR is sometimes possible). If we go under the nominal formulations, it is not really a contradiction that we find. What we find is, rather, that MC actually never performs what I consider as a genuine translation preserving the IR, that is, a T IR. The way MC frames the problem of incommensurability, joined to the awareness that in his second try one is actually not looking for linguistic items satisfying the clause ‘sameness of IR’, strongly suggests the need of something like a ‘third try’ corresponding to the search for a T IR. Had MC seriously attempted to follow such a third try, he would certainly have been led to the difficulties, examined above, constitutive of any comparative judgment of IR in the framework of an holistic theory. True, MC mentions, in his analysis of the historical examples, similar patterns of theoretical relations between L1 of T1 and L2 of T2 (for instance, the fact that ‘velocityED’ and ‘velocitySR’ are involved in some identical mathematical formulas). But such remarks are not exploited as the starting point of a general methodological discussion concerning the pretension that linguistic items are analogues with respect to IR; neither are they exploited as premises of the conclusion according to which certain linguistic items (the non-incommensurable ones) indeed possess homologue IR (are T IR). 150 Léna Soler

at first sight as potential candidates for mutual translation, as MC underlines too — and this is an important point of agreement be- tween us). • Moreover, some incommensurable concepts of the so-called incom- mensurable theories must have the same CA1 (at least in the re- stricted sense): there must be concepts of T1 and T2 that are simi- larly linked with — in the minimal sense of ‘being relevant for the characterization of’ — a non negligible number of identical empir- ical situations. Otherwise, the two theories T1 and T2 would not appear as rival incommensurable theories, but as theories about different separated regions of reality — like for instance hydro- dynamics and botany. And in that case the claim that T1 and T2 are incommensurable is neither scandalous nor interesting, and the comparison between T1 and T2 no longer appears as a crucial epistemological problem linked to realism and relativism).

With such (indeed incomplete but already far too long) characteri- zation of incommensurability, we lose the nice symmetry of MC’s con- clusion. But we gain, I hope, in precision.

Notations

T = any theory. T 1/T 2 = old/new competing theories. L = any linguistic item (signifier or group of signifiers forming an expression or a sentence). L1/L2 = a linguistic item used in the theoretical context T1/T2. ED = electrodynamics. SR = Special Relativity. t1/t2 = MC’s first/second try. t1a/t2a = first step of MC’s first/second try. t1b/t2b = second step of MC’s first/second try. CA = conditions of application. IR = inferential relations. ‘CA1 of L’ (or conditions of application in the first sense) = ‘empirical situations to which L is linked in the the- oretical context T ’. Incommensurability on the basis of a contextual theory of language 151

L applies1 (or applies1 to this or that particular empirical situation) = L indeed has links to empirical situations (or is in- deed linked to this or that particular empirical situ- ation) in the theoretical context T . ‘CA2 of L’ (or conditions of application in the second sense) = ‘empirical adequacy of the description named L’, ‘ex- istence of the state of affairs named L’, or ‘truth of the statement L’ from the viewpoint of a given sub- ject (most of the time a scientific community in the context of our discussion). L applies2 = L has an empirical objective counterpart, L is not an empty concept (from the viewpoint of a specified subject). T IR1(= T IR) = to look for, within two theories T1 and T2, two lin- guistic items having the same inferential relations (items associated with superimposable structures) = the operation attempted in t1b = a genuine ‘translation satisfying the condition same inferential relations’, that can thus be noted T IR. T IR2(= G) = to graft, on a linguistic item L1 of T1, a foreign net- work of IR usually associated with an item L2 in the theoretical context T2 = the operation attempted in t2a, inadequately de- scribed as a translation according to IR. What is done in t2a is not an operation of translation. It can be better described as a graft (= G) . Ei = an empirical situation. Sa = the subject of an application1 (= a linguistic item). Pa = the point of an application1 (= a set of empirical situations Eis). Ra = the relation constitutive of an application1; the kind of link holding between Sa and Pa. Eiobj = the objective Eis = empirical situations taken to be manifestations of the reality under study. Eimes = the measuring Eis = experimental situations con- ceived and performed in order to measure some the- oretical variables. 152 CA CA Pa Ei 1obj = 1 such that = some obj (and correlatively such that Ra = ‘to be relevant in order to achieve a sound characterization of the objective situation under study’). CA CA Pa Ei 1mes = 1 such that = some mes (and correlatively such that Ra = ‘to be relevant and reliable in order to determine the magnitudes involved in some theory’). IREi = network of the inferential relations underlying the descriptions of the Eis. IR DL = network of the inferential relations underlying the definition (D) or the sense of a theoretical linguistic item L. IRB IRB [L−Ei] or = network of the inferential relations underlying the description of the way L is linked to the Eis; bridge relations between theoretical assumptions and obser- vational states of affairs. CA1 of L in the restricted/enlarged sense = CA1 restricted to the specification of the Eis IR L IR CA (= Ei) to which (= DL ) applies1 / 1 un- derstood as including the additional specification of the way L is linked to the Eis (=additional specifi- IRB cation of [L−Ei] ). Incommensurability and Dynamic Conceptual Structures

Hanne Andersen University of Copenhagen

Résumé : Un problème important à propos de l’incommensurabilité est d’ex- pliquer comment des théories qui sont incommensurables peuvent néanmoins entrer en compétition. Dans cet article, on examine brièvement le compte rendu kuhnien de la différence entre transitions conceptuelles révolutionnaires et non révolutionnaires. On argue que l’approche taxonomique kuhnienne et le principe de non-recouvrement qui le sous-tend ne suffisent pas à distinguer entre ces deux types de transition. On montre que cette approche s’appuie principalement sur des analyses de corrélations entre traits, alors qu’il est né- cessaire de prendre de plus en considération les explications en vigueur de ces corrélations entre traits. Ceci met l’accent sur les théories, un élément qui n’a joué qu’un rôle modeste dans le travail que Kuhn a consacré aux lexiques scien- tifiques des années 1980 au début des années 1990. On argue que sur la base de ce compte rendu élargi des structures conceptuelles, l’incommensurabilité cor- respond à des corrélations qui d’un côté portent sur des traits présentant des recouvrements et de l’autre sont subsumées sous des explications différentes. Abstract: One important problem concerning incommensurability is to ex- plain how theories that are incommensurable can nevertheless compete. In this paper I shall briefly review Kuhn’s account of the difference between rev- olutionary and non-revolutionary conceptual developments. I shall argue that his taxonomic approach and the no-overlap principle it entails does not suffice to distinguish between revolutionary and non-revolutionary developments. I shall show that his approach builds mainly on analyses of feature correlations, and that it is necessary to include explanations of these feature correlations as well. This puts emphasis on theories; an element which has played only

Philosophia Scientiæ, 8 (1), 2004, 153–168. 154 Hanne Andersen a humble role in Kuhn’s work on scientific lexicons from the 1980s and early 1990s. I shall argue that on the basis of this extended account of conceptual structures, incommensurability can be understood as overlapping feature cor- relations that are covered by different explanations.

1. Incommensurability: the main challenge and the standard replies

When Kuhn in The Structure of Scientific Revolution claimed that “the normal-scientific tradition that emerges from a scientific revolution is not only incompatible, but often actually incommensurable with that which has gone before”, he ignited a series of debates about scientific change, theory choice, and the status of scientific entities. One of the main chal- lenges of the incommensurability thesis has been to explain how theories that are incommensurable can nevertheless compete. As Shapere for- mulated the challenge in one of the first reviews of The Structure of Scientific Revolutions: “if they disagree as to what the facts are, and even as to the real problems to be faced and the standards which a suc- cessful theory must meet — then what are the two paradigms disagreeing about? And why does one win?” [Shapere 1964, 391]. This is a serious challenge that has shown very difficult to handle. Even Kuhn have let himself confuse by the issue when at the beginning of the 1990s he claimed that new subspecialties and the specialty from which they emerged were also incommensurable ([Kuhn 1992, 19f/120]; the second pages mentionned in the references of Kuhn correspond to [Kuhn 2000]). Ironically, this hits the core of Shapere’s old, but still unanswered question: how to make sense of the idea that incommensu- rable theories are actually competing. Intuitively, one would say that the fact that there is no or only little communication between differ- ent subspecialties — like solid state physics and neural nets research — reflects only that they address ‘something different’, that they are not ‘about the same thing’. But for such theories as the oxygen theory and phlogiston theory one would indeed say that they are ‘about the same thing’ and that they therefore compete on offering the better account of their common domain — even though it has remained an open question what should be understood by ‘common domain’. In the discussions about how to understand the common domain of incommensurable theories, realists have tried to meet the challenge inherent in Shapere’s question by claiming that later theories are better descriptions of the same entities that earlier theories referred to, and that the common domain can be established through this referential stability Incommensurability and Dynamic Conceptual Structures 155

[Putnam 1975a]. On the opposite side, non-realists have argueed that although object-domains cannot be understood in any theory-neutral way, incommensurable theories do in some sense share object domain. None of these attempts to meet the challenge seem to pay due respect to the incommensurability thesis insights. The realist approach seem to discard the historical observation inherent in the incommensurability thesis that, occasionally, scientific terms do change reference. However, if realists start allowing referential change, they seem to be slowly sliding away from their unchangeable natural kinds populating the world. On the other side, when non-realists call for a shared object domain they seem to be slowly sliding in the direction of fixed world populated by unchangeable natural kinds. Apparently, both realists and non-realists seem to be sliding away from their original position towards that of their opponent, but none of them providing a satisfactory solution to Shapere’s question. However, a different approach to the problem of incommensurability has been taken by [Shapere 1989], [Shapere 2001] and later adopted by cognitively inclined scholars, such as [Nersessian 1984], [Nersessian 2001]. Shapere has argued that the problem of incommensurability has often been seen as the problem of how to compare individual concepts from two theories, in isolation from all other considerations. However, on his view, the interesting issue is not that of such side-by-side comparisons, but that of “tracing the reasons for adoption of successive alterations which result in the appearance of radical, ‘incommensurable’ change” [Shapere 2001, 199]. Such an approach makes it possible both to recognize the depth of the change and to explain how it has taken place. This approach has been developed further by Nersessian in her stud- ies of the micro-processes of conceptual change seen as a problem-solving process. On her view, conceptual changes — such as the disappearance or creation of concepts, or the absorption of significant aspects of appar- ently eliminated concepts into other concepts — are continuous but not simply cumulative [Nersessian 1984], [Nersessian 2001]. The chain-of-reasoning connections may thus explain continuity and the possibility of comparison, but this calls for an analysis of possible differences between revolutionary and non-revolutionary change. In this paper I shall briefly review Kuhn’s account of the difference between rev- olutionary and non-revolutionary conceptual developments. I shall argue that his taxonomic approach and the no-overlap principle it entails does not suffice to distinguish between revolutionary and non-revolutionary developments. I shall show that his approach builds mainly on analyses of feature correlations, and that it is necessary to include explanations 156 Hanne Andersen of these feature correlations as well. This puts emphasis on theories; an element which has played only a humble role in Kuhn’s work on scientific lexicons from the 1980s and early 1990s. I shall argue that on the basis of this extended account of conceptual structures, incommensurability can be understood as overlapping feature correlations that are covered by different causal explanations.

2. Kuhn’s account of conceptual hierarchies

In The Structure of Scientific Revolutions incommensurability was char- acterised broadly as a difference in the set of problems and standards for problem solutions, in ontological commitments, and in meaning. How- ever, Kuhn later focussed explicitly on concepts and conceptual struc- tures in defining incommensurability. In his writings from the 1980s, Kuhn identified revolutionary developments with those that demand a restructuring of the conceptual structures, in contrast to developments that imply only additions or refinements to an existing structure. This distinction was based on the view of a conceptual structure as a mul- tidimensional network in which concepts are tied together or distanced from each other by the criteria that can be used to identify referents of the terms in question. On this view, incommensurability is the result of developments that change the constitutive linkages between concepts, whereas conceptual refinements or other developments that preserve the overall structure do not imply incommensurability [Kuhn 1983aa, 683/52]. In discussing incommensurability, Kuhn’s main focus from the 1980s and onwards was on taxonomic terms, or kind terms, that is, terms “which refer to the objects and situations into which a language takes the world to be divided” [Kuhn 1990b, 4]. The taxonomic conceptual struc- tures was seen as ‘categorisation modules’ [Kuhn 1990b, 5] in which “cer- tain sorts of expectation about the world are embedded” [Kuhn 1990b, 8]. On this view, incommensurability denotes the relation that “some of the things which can be conceived and described using one [lexicon] can’t even be imagined with the other. They require a different lexicon which would in turn render unimaginable some of the things permitted by the first” [Kuhn 1990b, 9]. This barrier to certain kinds of ontological enrichments is deeply embedded in Kuhn’s theory of concepts. One of the major premises for this theory is a mutual dependence between concepts and objects which Kuhn expressed through the rhetorical question “Does it obvi- ously make better sense to speak of accommodating language to the Incommensurability and Dynamic Conceptual Structures 157 world than of accommodating the world to language. Or is the way of talking which creates that distinction itself illusory? Is what we refer to as ‘the world’ perhaps a product of a mutual accommodation between experience and language?” [Kuhn 1979, 418/207]. However, Kuhn’s on- tological viewpoint may be difficult to extract from his writings which suffer from a tension between two different meanings of key terms such as ‘world’ in passages like “though the world does not change with a change of paradigm, the scientist afterward works in a different world” [Kuhn 1970a, 121]. To resolve this tension, [Hoyningen-Huene 1989] has suggested a reconstruction in which two concepts of ‘the world’ have to be distinguished: the world-in-itself which is a “hypothetical fixed na- ture” [Kuhn 1970a, 118], [Hoyningen-Huene 1989, chapter 2.1], and the phenomenal world which is a “perceived world” [Kuhn 1970a, 128], that is, “a world already perceptually and conceptually subdivided in a cer- tain way” [Kuhn 1970a, 129]. The subdivision is not read off from the world itself, but is a structure which is imposed on the world by means of the concepts applied to it. On this point Kuhn rejects the realist idea that ‘the world can be cut at its joints’. Instead, different conceptual structures may constitute different ontologies. The conceptual structure is established by relations of similarity and dissimilarity between perceived objects. In accounting for the constitu- tion of the phenomenal world through relations of similarity and dissim- ilarity, Kuhn ascribes a special importance to dissimilarity, that is, the features which differentiate between instances of contrasting concepts. It is important to note that in including dissimilarity in the account, his interest is not in dissimilarity between members of any pair of arbitrary categories. Instead, what is of interest is the relation of dissimilarity that holds between members of categories which can be mistaken for one an- other. Such instances of categories that can be mistaken for one another must be more similar to one another than to instances of other concepts. Hence, these categories again form a family resemblance class at the superordinate level. Or, if seen from the other direction, this superor- dinate can be exhaustively decomposed into the set of non-overlapping categories formed by the contrast set. On this analysis, family resem- blance concepts form hierarchical structures in which a general concept decomposes into more specific concepts that may again decompose into yet more specific concepts, and so forth — in other words, taxonomies30. On this taxonomic view, the decomposition of a superordinate con- cept into a group of contrasting concepts is determined by sets of fea-

30For a full a detailed analysis of Kuhn’s family resemblance account of concepts, see e.g. [Andersen 2000]. 158 Hanne Andersen tures. Thus, as emphasised by Kuhn, “to each node in a taxonomic tree is attached a name (. . . ) and a set of features useful for distinguishing among creatures at the next level down. (. . . ) Attached features are not shared by named creatures. They function as differentiae for the next level down” [Kuhn 1990b, 5] (emphasis in the original). The emphasis on contrast sets and the features that differentiate be- tween the individual categories in the set may seem as if Kuhn is taking recourse to definitions per genus et differentiam. However, this is not the case; the subdivision of a superordinate into a set of contrasting con- cepts is not defined by particular differentiae specificae, but by patterns of dissimilarity that may be overlapping and criss-crossing, and which may differ for different speakers. This is in consonance with a point which Kuhn has noted throughout his writings on conceptual structures, namely that there are no restrictions on which characteristics that may be used to judge objects similar or dissimilar. For Kuhn, there is no distinction between defining and contingent features. By the same to- ken, different people may draw on different features when identifying instances of a category, as long as they successfully ascribe any given instance to the same category31. One may also note that this view was developed in an effort to reject the traditional realist position that the world can be cut at its joints. In consonance with that, features should not be interpreted in a simple realist way either. Features may come into existence as the result of our interaction with the world, for example by the introduction of a new in- strument that reacts in different ways in different situations ([Andersen 2000, 321]; similar views can be found in [Lakoff 1987] and [Buchwald 1992]).

3. Vindication from cognitive psychology

Similar views of concepts as based on a network of similarities and dis- similarities have also been developed by cognitive psychologists, most

31It is important to note that Kuhn’s point here is very different from the division of linguistic labor introduced by [Putnam 1975a]. Putnam argues that “the features that are generally thought to be present in connection with a general name (. . . ) are all present in the linguistic community considered as a collective body; but that collective body divides the ‘labor’ of knowing and employing these various parts of the ‘meaning’ of ‘gold”’ [Putnam 1975a, 228]. On that view, for a person to use the concept ‘gold’, he or she does not need acquire the method of recognizing if something is or is not gold. On Kuhn’s view, on the contrary, different speakers may draw on different features in recognizing if something is gold, but it is a prerequisite for being a member of the relevant language community that gold is recognized correctly as judged by the rest of the community. I shall return to this issue in section 6 below. Incommensurability and Dynamic Conceptual Structures 159 notably Eleanor Rosch and her collaborators. Beginning in the 1970s they made a series of studies of how individuals from different cultures and in different situations group objects into categories [Heider 1972], [Rosch 1973a], [Rosch 1973b], [Rosch & Mervis 1975], [Rosch et al. 1976]. They found that individuals classify objects not only as members of par- ticular categories but also as better or worse examples of the category. This variation in the goodness of example became known as “graded structures” of concepts. The existence of graded structures showed that classification was not a matter of sharing a list of defining features, since on such a view all concepts falling under a concept would do so in virtue of sharing the same list of features and would therefor have to be equal as instances of the concept. Based on empirical explorations of the hypoth- esis that the members of categories which are considered most typical are those that share the most features with other members, Rosch and her collaborators concluded that family resemblance offers an alternative to criterial features in defining categories. By the mid-1980s, the replace- ment of the classical account of concepts in terms of definition with a family resemblance account was referred to as “the Roschian revolution” [Neisser 1987, vii]32. On Rosch’ view, family resemblance is a matter of overlapping at- tributes that reflect “the correlational structure of the environment in a manner which renders them maximally discriminable from each other” [Rosch & Mervis 1975, 575]. Thus, “combinations of attributes of real objects do not occur uniformly. Some pairs, triples, or n-tuples are quite probable, appearing in combination sometimes with one, sometimes an- other attribute; others are rare; others logically cannot or empirically do not occur [Rosch et al. 1976, 383]. Further, just like Kuhn empha- sized the role of dissimilarity and contrast sets, Rosch also stressed that concepts “do not occur in isolation. Any time one places an item into one category one is simultaneously not placing it into other contrasting categories” [Rosch 1987, 157]. Kuhn’s favorite example of concepts based on similarities and dis- similarities between instances were the categories ‘duck’, ‘goose’ and ‘swan’. This contrast set forms part of a taxonomy in which the cate- gory ‘bird’ is attached to a set of features that can be used to distinguish among its subordinate categories ‘waterfowl’ and ‘songbird’. Among

32Although the replacement of the classical account with a family resemblance account was widely accepted, its detailed structure is still a matter for debate. Thus, a variety of different accounts have been introduced that generate phenomena like graded structures in different ways. For detailed accounts of the development, see e.g. [Lakoff 1987], [Barsalou 1992], [Margolis & Laurence 1999]. 160 Hanne Andersen these distinguishing features are, for example webbed/unwebbed feet, rounded/pointed beak, etc. To the category ‘waterfowl’ is attached a new set of features that can be used to distinguish among the subordinate cat- egories ‘duck’, ‘goose’ and ‘swan’. Among these distinguishing features are, for example, the neck/head-length ratio, the body width/length ra- tio, color, etc. (figure 1).

Figure 1: Partial taxonomy covering waterfowl. From [Kuhn 1990b]. Re- produced with permission from the MIT Institute Archives and Special Collections. Incommensurability and Dynamic Conceptual Structures 161

When distinguishing between ducks, geese and swans some speakers may use the combination of the two features neck/head-length ratio and body width/length ratio, while others use the combination of the two features colour and neck/head-length ratio. Each of these sets of features are jointly sufficient to identify instances of the contrasting concepts, but none of the features are individually necessary. In discussing taxonomic structures constituted through relations of similarity and dissimilarity between instances, Kuhn never went beyond simple examples like that of waterfowl. Based on these examples he claimed that “the same technique, if in a less pure form, is essential to the more abstract sciences as well” [Kuhn 1974, 313]. For example, bacteria and vira form part of a taxonomy in which the category infectious agents is attached to a set of features that can be used to distinguish among its subordinate categories (figure 2)33:

Figure 2: Partial taxonomy covering infectious agents.

One may note that in the analysis of taxonomies, the various features are not all equal. Instead, some features are values of others. For ex- ample, the feature ‘feet’ is an attribute of birds that can take the value ‘webbed’ or ‘unwebbed’. Thus, it is differences in values that distinguish between contrasting categories, but all are values of the same attribute. As argued by [Barker, Chen & Andersen 2003] this kind of taxonomy is easily represented by means of frames. Figure 3 is a partial frame representation of ‘bird’.

33For detailed analysis of scientific examples, see [Barker’s 2001] analysis of the Copernical revolution or [Andersen & Nersessian 2000]’s analysis of electrostatics. 162 Hanne Andersen

Figure 3: Partial frame of ‘bird’

Further, one may note that although Kuhn stressed that features function as differentiae, they serve this function because they are shared by instances of contrasting concept on the next level down. Both Kuhn’s and Rosch’ views are therefore based on the idea that instances of a category in a contrast set share a bundle features that at the same time distinguishes them from instances of other categories. The frame representation shows how all instances of the concepts in a contrast set share some features, and how these common features are related to the features that can be used to differentiate between them. In the above frame representation of the concept ‘bird’, all exemplars of ‘bird’ share the attributes ‘feet’, ‘beak’ and ‘body’, but the values of these attributes vary between the subordinate categories ‘waterfowl’ and ‘songbird’. However, the distinction between attributes and values is not to be understand as a distinction between features that are different in kind as such, but as a distinction that shows how features of a given concept are related to each other with respect to this particular concept and taxonomy of which it forms part. Thus, while the concept ‘bird’ has the attribute ‘beak’ whose different values can be used to distinguish between various subordinates, the concept ‘animal’ has the attribute ‘mouth parts’ which can have different values such as ‘beak’ or ‘lips’.

4. Correlations and anomalies

Obviously, Kuhn’s claim that the similarity and dissimilarity relations may be based on different features presupposes an empirical correlation between all features in the bundle attached to a given category. As only some of those co-occurring features are necessary to use a given concept Incommensurability and Dynamic Conceptual Structures 163 correctly, adding further features will say something not just about how to pick out instances of the concept, but also something about how an object already picked out will behave.The conjunction of all features can therefore be seen as a hypothesis about the behavior of the instances of the corresponding concept. In this way conceptual structure is linked to projectibility. For a concept to be projectible, the expectation must exist that the total set of features that are involved in the relations of similarity and dissimilarity involve more features than needed to pick out instances of the concept, and that the classifications which the different sets of jointly sufficient features give rise to must be co-extensive34. It is a key premise of Kuhn’s position that the claim whether this correlation between features holds has an important objective compo- nent. Although the features may be the result of our interaction with the world, once they have been posited, they cannot be correlated ar- bitrarily. The world will show if an alleged correlation does not hold, since in that case instances that violate the correlation will eventually be discovered35. Hence, although a conceptual structure has proved to be a fully consistent division of the object domain for all previously known objects, a new object may still reveal it as inconsistent. Claiming that the question whether the bundle of features attached to a given category is actually correlated has an objective component, Kuhn introduces a resistance against giving arbitrary structures to the phenomenal world. If one tries to impose arbitrary structures to the phenomenal world, situations will appear in which it becomes clear that objects do not behave or situations do not develop as prescribed by the current conceptual structure. As Kuhn expresses his view: “nature can- not be forced into an arbitrary set of conceptual boxes. On the contrary (. . . ) the history of the developed sciences shows that nature will not indefinitely be confined in any set which scientists have constructed so far” [Kuhn 1970b, 263]. Similar views are expressed by cognitive psychol- ogists who also emphasize that “the environment places constraints on

34Again, the lack of distinction between defining and contingent features is crucial since that dissolves any clear distinction between the knowledge of which objects exists and the knowledge of how they behave. See also [Hoyningen-Huene 1989, chapter 3.7]. 35Kuhn ended up ascribing this objective component to the world-in-itself. Ad- mittedly, he first tried to avoid the use of Kantian things-in-themselves [Kuhn 1979, 418f./207], but later changed his mind: “Underlying all these processes of differenti- ation and change, there must, of course, be something permanent, fixed, and stable. But, like Kant’s Ding-an-sich, it is ineffable, undescribable, undiscussible. Located outside of space and time, this Kantian source of stability is the whole from which have been fabricated both creatures and their niches” [Kuhn 1990c, 12/104] (italics added). 164 Hanne Andersen categorisations. Human knowledge cannot provide correlational struc- ture where there is none.” [Rosch et al. 1976, 430]. This claim that there is some kind of resistance against giving arbi- trary structures to the phenomenal world does not rule out that features can be correlated in different ways. Instead, different sets of similar- ity and dissimilarity relations may assume correlations between different sets of features which carve different joints in the phenomenal world. Thus, one may note that the claim is a purely negative claim that not any arbitrary bundling of features is possible; it is not a positive claim about the existence of a privileged set of features bundles constituting the world’s real joints. The claim is therefore far from a traditional realist position [Andersen 2001]. Since the conceptual structure is constituted by the relations of simi- larity and dissimilarity and the bundles of features that result from these, an object which challenges the decomposition of the superordinate into a contrast set of non-overlapping subordinates will call this structure into question. This is what Kuhn introduced as the no-overlap principle:

no two kind terms, not two terms with the kind label, may overlap in their referents unless they are related as species to genus. There are no dogs that are also cats, no gold rings that are also silver rings, and so on, that’s what makes dogs, cats, silver, and gold each a kind. Therefore, if the members of a language community encounter a dog that’s also a cat (or, more realistically, a creature like the duck-billed platypus), they cannot just enrich the set of category terms but must instead redesign a part of the taxonomy [Kuhn 1990b, 4/92].

According to this principle, a conceptual structure is challenged if an object is discovered that on the basis of different differentiating fea- tures can be ascribed to different contrasting categories, since it then reveals that the bundlings of features implied in the contrast set was not projectible. However, a set of differentiating features may generate a large field of potential feature bundles and associated concepts in the form of all possible combinations of the features. Of these potential feature cor- relations only some will be found empirically. The question is whether the discovery of an instance with a previously unseen combination of features within this conceptual field is therefore ruled out? Or if only some of the yet unseen combinations are ruled out, while others can be discovered without calling for changes in the conceptual structure. We may have discovered that birds living in water have webbed feet and that Incommensurability and Dynamic Conceptual Structures 165 big waterfowl with long necks are white, but does that suggest that it is as severe to discover the first black swan as it would be to discover a bird that lives in water but which has unwebbed feet? There seems to be a need for a distinction between possible but yet undiscovered correlations and impossible correlations.

5. Explanations

A possible distinction of this sort may be based on the existence of ex- planations of the correlations. As a reaction to the family resemblance account of concepts developed by Rosch and her collaborators, critics have argued that if the categories should divide the world simply on the basis of features appearing together in bundles, “there are so many possible correlations that it is not clear how the correct ones get picked out” [Murphy & Medin 1985/1999, 430]. As a solution to this problem Murphy and Medin pointed out that people tend to deduce reasons for feature correlations, claiming that “feature correlations are partly sup- plied by people’s theories and that the causal mechanism contained in theories are the means by which correlational structure is represented” [Murphy & Medin 1985/1999, 431]. This view offers a distinction between theoretically possible and the- oretically impossible correlations based on whether they can be covered by the currently accepted explanations. Thus, the discovery of an in- stance with a previously unseen combination of features that can either be explained or at least does not violate currently accepted explanations of feature correlations may lead to the introduction of a new category as a mere refinement of the conceptual structure. On the contrary, com- binations of features that violates accepted explanations of feature cor- relations constitute such anomalies that they call conceptual structure into question. For example, given a theory involving evolutionary expla- nations of the correlation between birds having webbed feet and living in water, the discovery of a bird with unwebbed feet living in water will be a severe anomaly. In contrast, without explicit explanations of the correlation of colour and e.g. neck length, the discovery of a black swan may be surprising, given that all previous examined exemplars have been white, but the new subcategory may be added to the taxonomy un- problematically. Or, to take more recent scientific examples, while the discovery of new bacteria or vira with e.g. variant morphological features may lead to the unproblematic addition of a new concept subordinate to ‘infectious agent’, the discovery of an agent that can transmit disease, but which shows features usually associated with proteins rather than 166 Hanne Andersen features associated with nucleic acid is very anomalous indeed. Again, the difference may be found in the existence of explanations of feature correlations, such as the central dogma of molecular biology that links replication with nucleic acid36. This account may also help explaining why anomalies are not all equally severe. It is a well-known aspect of family resemblance accounts of concepts that different instances of a particular concept may vary in how good an example of the concept they are. Thus, some instances may be better examples than others by being more similar to each other or more clearly dissimilar to instances of contrasting concepts. This variation in the status of instances is called a concept’s graded struc- ture. These differences in goodness-of-exemplar may affect whether an anomalous object questions the conceptual structure. Thus, if an ob- ject is encountered that judged from different features is a good exam- ple of two contrasting concepts it clearly questions the adequacy of the conceptual structure. On the other hand, if an object is encountered that judged from different features is a poor example of two contrasting concepts it may not call the conceptual structure in question as such. Instead, it may just suggests that further research may be necessary to find out whether a new category exists, or if the existing categories may show some additional features that allows the objects to be unequivo- cally assigned to one of them. In the former case, the object is a severe anomaly, in the latter case it is not. Often the theories that has been elaborated to explain the feature cor- relations inherent in the conceptual structure will also determine which features are considered central [Ahn 1998], and by the same token which instances of the concept are judged as good and poor examples according to their possession of central features. The severeness of an anomaly — and thereby the triggering of conceptual change — is therefore closely linked to the theory explaining feature correlations37.

6. A dynamic perspective

When an anomaly has questioned whether the purported correlations of features are actually projectible, conceptual structure must be changed. However, an anomaly only shows that a particular bundling of features is not projectible, it does not determine how they should be bundled instead. The requirement in examining alternatives is that in the new

36A detailed study of this case lies outside the scope of this paper; for further details see e.g. [Keyes 1999a], [Keyes 1999b], [Poulsen & Andersen 2004]. 37For a historical illustration of this point, see [Andersen, forthcoming]. Incommensurability and Dynamic Conceptual Structures 167 conceptual structure the anomalous object will be ascribed to only one of the contrasting concepts. Such a change implies changes in the relations of similarity and dissimilarity and hence changes both of the bundlings of features and of the causal explanation of the feature correlations, where the guideline is that projectibility must be re-established by bundling the features such that the new combinations of features can be seen as hypotheses with some positive, but no negative cases. Hence, the conceptual structure will be changed to provide a new division which is consistent for the new, enlarged group of known objects. On this view, conceptual structures are clearly dynamic entities which under certain circumstances may be subjected to change. This dynamic perspective is essential in analysing conceptual struc- tures. On this perspective, a conceptual structure is always given in some form by the preceding generation which passes it on to the next. This was clearly emphasised by Kuhn, when he pointed out that novices always

find the world already in place. (. . . ) Creatures born into it must take it as they find it. They can, of course, interact with it, altering both it and themselves in the process, and the populated world thus altered is the one that will be found in place by the generation which follows [Kuhn 1991, 10].

Hence, the important issue is not the synchronous constitution of a con- ceptual structure, but the process in which it can be transmitted over time. The analysis of correlations between features and explanations of the correlations should therefore not be read as an analysis of how a con- ceptual structure may be established from scratch, invoking the question of whether correlations or explanations are primary. On a dynamic per- spective, the question of primacy vanishes since some correlations and explanations are always given from the historical setting, even if only in a primitive form. In the historical process they may from there again be transformed into other correlations and other explanations38.

7. Incommensurability and overlapping phenomenal worlds

It is possible to imagine several different changes of the bundling of features which all have some positive, but no negative cases. If these

38For an elaborate version of this argument, see [Andersen 2000], [Andersen 2001]. A simple historical example of such a historical development of a simple conceptual structure can be found in [Andersen 2002]. 168 Hanne Andersen different bundlings overlap, that is, share some but not all features in the bundle, then they can be seen as incompatible hypotheses, which are nevertheless all projectible. As the different bundlings carve different joints in the phenomenal worlds to which they give rise, although they are all projectible, they are projectible in different phenomenal worlds. Given Kuhn’s theory of the constitution of phenomenal worlds and their joints, identical phenomenal worlds are those which are carved into the same joints, that is, phenomenal worlds which share ontology. For phenomenal worlds to be carved into the same joints presupposes shared conceptual structure, and that again presupposes shared relations of similarity and dissimilarity. However, as argued above, the similarity and dissimilarity relations constitutive of the conceptual structure need not be attached by means of the same features by all speakers. Hence, it is shared structure, not shared features, that yields shared ontology. The only requirement is that in so far as features are not shared, it is expected that they are all compatible and covered by the same causal explanation of the correlations. Hence, in so far as the features for a given set of contrasting concepts are not shared, it is expected that they can in principle all be bundled, that is, that all the different sets of jointly sufficient features used by different members of the language community are empirically correlated and included in the same causal explanations of the correlation. Only in this case will members of the language community who use different fea- tures to distinguish instances of a set of contrasting concepts categorize these instances in the same way. But these phenomenal worlds do not differ in any arbitrary sense. They are not unrelated. The important point is that the different bun- dles are incompatible due to the shared features. Because of the under- lying causal explanations of the bundling, the one bundle cannot simply be extended by the remaining features of the overlapping bundle. These are the features ruled out by the causal explanation of the bundling. That means that the feature bundles give rise to different phenomenal worlds that are also mutually exclusive. If you adopt one, you simulta- neously reject the others. Hence, while it is shared structure and not shared features that yields shared ontology, when structure is no longer shared, it is shared features that provides the overlap between different phenomenal world necessary for them to compete in offering the better account of the world in the form of more successful or more promising bundlings. On the Grammatical Aspects of Radical Scientific Discovery∗

Aristides Baltas National Technical University, Greece

Résumé : La découverte scientifique radicale, et le changement radical de paradigme associé, sont traités ici comme découlant de la mise à jour de ce qu’on appelle des ‘assomptions’ d’arrière-plan. Celles-ci sont considérées comme plus ou moins équivalentes aux ‘propositions charnières’ discutées par Wittgenstein dans De la certitude. Sur cette base, diverses questions liées aux changements de signification, au changement théorique, à l’incommensurabilité, etc., sont discutées. On montre que la conception d’ensemble de Kuhn, une fois précisée, n’implique ni l’idéalisme ni le relativisme, et que la rationalité

∗A first version of the present paper was presented at the conference on “The Legacy of Thomas S. Kuhn”, organized by Jed Buchwald at the Dibner Institute, MIT, Cambridge, Mass., on November 20-22, 1997. In addition to Jed, it is both a duty and a pleasure to thank all the participants, and especially Jim Conant (and, as he well knows, for more reasons that this), Mike Mahoney and Norton Wise for their comments and criticisms. A second version of the paper was presented at the workshop on Kuhn organized by Alexander Bird and Rupert Read in Norwich, U.K., on August 30, 2002. It is again both a duty and a pleasure to thank my hosts both for the workshop itself and for their active interest in the paper. All the participants helped me with their criticism but I feel I should single out Vasso Kindi, Jean- Philippe Narboux and Léna Soler. At home, the comments of Aristidis Arageorgis, Charis Chronis, Andreas Karitzis, Dimitri Papagiannakos, Stathis Psillos, Kostas Stergiopoulos, George Fourtounis and, of course, Peter Machamer were, as always, to the point. Last but by far not least, the copious and incisive comments of Léna Soler, once again, as well as those of a particularly generous anonymous referee, of the kind justifying the existence of the refereeing system, obliged me to revise substantially the paper and make it much clearer. At least this is how I see it now.

Philosophia Scientiæ, 8 (1), 2004, 169–201. 170 Aristides Baltas et le progrès scientifique peuvent être sauvés d’une manière acceptable par les scientifiques praticiens. Abstract: Radical scientific discovery and the associated radical “paradigm change” are treated here as following from the disclosure of what I call back- ground ‘assumptions’. These are taken as more or less equivalent to the “hinge propositions” that Wittgenstein discusses in his On Certainty. On this basis, various issues connected to meaning variance, theory change, incommensura- bility and so forth, are discussed. It is shown that Kuhn’s overall account need not, with qualifications, imply either idealism or relativism while ratio- nality and scientific progress can be saved in a way that may be acceptable by practising scientists.

More and more signs are pointing nowadays at a revival of the issues opened by Kuhn’s work. Although social constructivism, in one or an- other form or guise, still holds center stage, a mounting series of essays, books or workshops try to raise again, in philosophically novel and in- teresting ways, questions of his that the prevalence, precisely, of social constructivism has more or less managed to push under the table. Cen- tral among such issues is the complex net of philosophical aporias which, to go quickly, we can call “radical scientific discovery”, without needing for the moment to presume anything regarding the discovery/invention debate and its cognates. To stay with Kuhn’s terminology, we can sim- ply say that a “radical scientific discovery” is the kind of event or episode — without, again, needing to presume anything of its temporal or other features — inducing1 a “paradigm change”. Among the various puzzling features of paradigm change, the ones concerning language (meaning variance and meaning change, incommen- surability and so forth) have received most attention. However, no gen- eral consensus regarding their resolution has been attained despite the valiant efforts dispensed for the purpose, not least of which were those deployed in Kuhn’s own later work. Trying to discuss some of the lin- guistic aspects of “scientific discovery” is what the present paper aims at. Kuhn’s recognized relation to Wittgenstein’s later philosophy2 offers an initial justification for my talking of grammatical aspects and allows me to proceed without further ado.

1“Induces” is here taken to refer as vaguely as necessary to the more or less causal relation holding between the event or episode of radical scientific discovery and the more complex and variously more extended process of paradigm change. Which is to say that, at least in the present stage of the discussion, “produces”, “causes”, “brings about” and so forth would be too strong. 2See, for example, [Kindi 2004]. Grammatical Aspects of Radical Scientific Discovery 171 1. Radical Scientific Discoveries: Giving Names to the Ungrammatical?

Let me start by recounting a personal experience as succinctly as possi- ble. This occurred in three stages. In the first stage, I was trying to present to my students some of the deeper motivations leading to the constitution of the new philosophical tradition that bears the name “analytic philosophy”. Behind Russell’s and Frege’s work lies, of course, Cantor’s theory of sets and the question of the infinite. Thus, in trying to explain Cantor’s main achievements to students who had never before heard anything of this, I tried to ‘recon- struct’ the logical — or rather grammatical — move that Cantor made in giving his famous definition of the infinite: a set is of infinite cardinal- ity if and only if its elements can be put into one-to-one correspondence with the elements of one of its proper subsets. What our author was up against before offering this definition was a total deadlock: on the one hand, since the set, say, of even numbers is a proper subset of the set of natural numbers, it obviously contains ‘fewer’ elements while, obviously again, the two contain an ‘equal’ number of elements, since these can be put into one-to-one correspondence. What Cantor did in order to escape was then very ‘simple’: he did not try to resolve or in any way overcome the contradiction but merely turned the very deadlock into a definition! “The paradise that Cantor has offered us”, to use Hilbert’s formulation, finds its initial grounds at precisely this point. At the time I did not think much about this. But later in the same course, I passed through the second stage of my experience. Now I was trying to provide a cursory account of the revolutions in physics that motivated, at least indirectly, much of the Vienna Circle philosophy of science. The name of Bohr thus inevitably appeared. In trying to reconstruct Bohr’s move now, the one that led to his theory of the atom, I ‘discovered’ myself following unawares the same explanatory pattern as in the case of Cantor. For reasons too complex to enter into either there or here, I took it for granted that Bohr could not — or would not — question either the electromagnetic theory of his time or the planetary model of the atom. But the two together demonstratively lead to an unstable atom: the accelerated motion of the revolving electrons makes them radiate and thus obliges them to fall onto the nucleus. If we deem unstable atoms unacceptable at any price, we have again a contradiction. For it is obviously contradictory to maintain together the electromagnetic theory, the planetary model of the atom and the latter’s stability. Bohr’s escaping from this deadlock can then be reconstructed 172 Aristides Baltas as similar in structure to Cantor’s. He refuses to succumb to or try to overcome the contradiction but goes unconcernedly forward by ‘simply’ turning this very deadlock into the definition of a new physical concept: atoms in the “ground state” do not radiate. Period. Which implies that the trajectories of the electrons in that newly defined state do not obey the classical electromagnetic laws and hence these can be no ‘real’ trajectories, whatever this might mean or imply. What exactly are they and where does their existence rely? Bohr gives no answer. Electronic ‘trajectories’ are precisely such that atoms in the “ground state” are stable analytically, by definition, and that is that. In other words, the electromagnetic theory and the planetary model of the atom both hold and there exist particular atomic states that are fully stable. Only that the latter are such simply because Bohr declares it! By mere fiat, with no reasons either sought or given3. There can be no doubt that this groundless decree made the then emerging quantum mechanics take a huge step forward. The third stage of my experience had nothing to do with the course in question. But it gave unexpectedly a name to what I had been ex- periencing. Thus, while I was reading a book on Lacan’s approach to psychoanalysis, I fell upon the following passage (I am translating from the original French):

(...) What is the object a?4 It is only a letter, nothing more than the letter a, a letter whose central function is to name a non resolved problem or, even better, to name an absence. Which absence? The absence of an answer to a question that persists unceasingly. Since we could not find the solution, which we required and we expected, we mark with a written sign — a simple letter — the opaque hole of our ignorance, we put a letter in the place of the answer we could not get. The object a signifies therefore an impossibility, a point of resistance to the theoretical development. Thanks to this notation, we can continue our research — despite our having stumbled– without breaking the chain of our knowledge. You see, the object a is finally an artifice of analytic thought designed to circumvent the rock of the impossible: we overcome the real by representing it by a simple letter (. . . ) [Nasio 1992, 125].

3Evidently, this simple picture does not intend to exhaust Bohr’s logical, concep- tual or experimental motivations for proposing his model of the atom; it does not seek to trace the history of this proposal, be it even in such a summary fashion; nor does it aim at reconstructing Bohr’s way of thinking on the issue. It only wants to suggest that radical scientific discovery carries important grammatical moves, the understanding of which may help us coming to grips with the philosophical issues involved. 4This is a Lacanian technical term the precise sense of which need not concern us here. Grammatical Aspects of Radical Scientific Discovery 173

With this everything fell into place. I now had at my disposal a concrete formulation, a name, for what I had been experiencing: radical scientific discovery, it seems, consists of a leap into the ungrammatical; it amounts to giving it a name by means of a novel definition. Let me formulate the point. Before the leap in question is taken, research within a given paradigm stumbles on a deadlock. In the pre- ceding examples this deadlock takes the form of an explicit contradiction and, as such, it constitutes a Kuhnian “anomaly” of the severest kinds, an anomaly that, for the cases that interest us here and as can be as- sessed ex post facto, cannot be handled by the means of the board, i.e. by the conceptual resources provided by the paradigm in place. How- ever, research does not stop for that matter. It takes cognisance, so to speak, of this impossibility and leaps forward by ‘simply’ giving it a new name, i.e. by turning that very deadlock or contradiction into a new positive definition. This new definition is positive in the sense that, by construction, it is in the position to ‘forget’, or, more psychoanalytically, to ‘repress’, its impossible origin while providing in this way the starting point of the succeeding paradigm. Given this, the view to be developed here boils down to the follow- ing: post festum, i.e. after the new paradigm has been set up and from the vantage point it defines, the anomaly in question can be character- ized as an encounter with the grammatical bounds of the old paradigm while the new definition starts instituting a novel grammatical space, the grammatical space supporting the new paradigm. This novel grammat- ical space enfolds, as it were, the very impossibility of the old paradigm to handle that anomaly and thus bears intricate relations to it, relations that we have to make precise5. To start doing this, we can consider such opening of a novel grammatical space as tantamount to the disclosure of what we will call background ‘assumptions’.

2. Scientific Concepts, Background ‘Assumptions’ and Grammatical Conditions

One more argument as to why the notion of paradigm — in the sense of “disciplinary matrix” — should replace the more traditional notion of theory is the following: no concept, either simple and intuitive or ab- stract and highly formalized, can exist, i.e. be understood and function within a process of inquiry, unless it carries along with it an amorphous

5Hence the two succeeding paradigms are not totally unrelated, as some views tend to present them. We will elaborate on this below. 174 Aristides Baltas plethora of what we can call background ‘assumptions’. These work ‘be- hind’ or ‘below’ the explicit definition of the concept to mutely adjust it to the language games it can partake, inside — but also outside — the scientific process of inquiry. We can say that these ‘assumptions’ support the concept’s manifest meaning by noiselessly dictating the con- ditions under which it makes sense; it is they that make up the latent grammatical conditions of the concept’s meaningfulness in the various contexts of its use. These ‘assumptions’ remain in the background for they perform their work silently, inexpressibly, hiding their work from view. Since on most views the meaning of a concept derives from the propo- sitions engaging it, it is to propositions we have to turn in order to assess the role and character of such ‘assumptions’ in respect to our present con- cerns. Thus some background ‘assumptions’ may render a proposition’s truth perfectly obvious while hiding themselves and the role they are silently playing in doing this behind the glare, so to speak, of that very obviousness. For example, on some such ‘assumptions’, the earth cannot but be immobile for anybody possessing her senses. On the other hand, some other background ‘assumptions’ may lie well concealed beneath our taking another proposition as totally inconceivable. For example, again on some background ‘assumptions’, no action at a distance can be conceived, for how can bodies react instantaneously to the presence of another faraway body when, in addition, there is nothing in between? As it is well known and as we will elaborate at length below, the de- velopment of classical mechanics has unearthed the ‘assumptions’ lying silently beneath the above propositions. And it has done that in a way making both this old obviousness and that old inconceivability appear today as astonishingly short sighted to almost everybody, i.e. to all those having gone through an elementary physics course. Moreover, such ‘assumptions’ may also work under a tautology, a contradiction, a deductive consequence or an analytic truth, mutely as- suring the logical status of the propositions concerned while again hiding themselves and their role from view6. Putnam’s example [Putnam 2000]

6For reasons that will become clearer below, I hesitate to use the qualification “apparent” in talking about such tautologies, contradictions etc, as I was at first inclined to: if logic is what it is standardly taken to be, tautologies, contradictions, etc. that depend for their logical status on background ‘assumptions’ can only be apparent tautologies, contradictions etc. Moreover, they are shown to be just that (or, at least, so it seems at first sight) after the disclosure of such ‘assumptions’, as I will be discussing shortly. However, the present paper looks to me as implying that we can never be logically or metaphysically certain that any tautology, contradiction, etc that we actually encounter will never turn into an apparent one in this sense. If Grammatical Aspects of Radical Scientific Discovery 175 is that somebody can be either naked or not naked and certainly not both, but only on at least the silent background ‘assumption’ that she is not wearing a net. It is well known that Lakatos’s “hidden lemmas” [Lakatos 1976] mess up rigorous deductive chains while it is analytically the case that the earth cannot be a planet, if the concept “planet” is indeed defined as referring to celestial bodies moving around the earth. This last example is to say that one of the obstacles physical astronomy (i.e. not that of merely “saving the phenomena”) had to overcome was that the empirical import of this definition was rendered perfectly obvi- ous by the work silently performed by some background ‘assumptions’ whilst such obviousness was going hand in hand with the self-evidence of the immobility of the earth and the background ‘assumptions’ assur- ing this self-evidence. The above entail that such ‘assumptions’ work in similar ways7 both for everyday concepts and those that mathematics and logic strive to define and to formalize rigorously, so as to strip them, precisely, of such possibly misleading background. On the present ac- count, even the most highly elaborated and worked out concept cannot but keep concealing the background ‘assumptions’ mutely assuring its meaningfulness. As Wittgenstein has shown (especially in his On Certainty), these are not proper assumptions — hence they should be placed within quotes. They are neither a priori and indubitable nor a posteriori and open to doubt. In normal circumstances, the role they are playing remains veiled and they cannot be moved around in the space of justifications. In Wittgenstein’s felicitous phrase [Wittgenstein 1969, §341-343] (see also [Morawetz 1980]), they are the “hinges” that have to stay put for the door of inquiry (its questions, its reasons, its doubts) to open and to remain open. It is in this sense that they constitute the latent quasi-logical, that is, precisely, grammatical, conditions allowing the concepts they support to have the meaning they do. Let me give a simple example by placing some of Putnam’s cats in this Wittgensteinian context. Normally, that is in Kuhn’s sense of “normal science”, the zoology of cats is not obliged to inquire, first, whether each of our purring compan- ions comes from two parents, whether they are all highly sophisticated robots or extra-terrestrials in disguise and so forth; to run, second, the appropriate tests; and to present, finally, explicit arguments to the effect that they are not. That our pets are no such things the zoology of cats this were indeed the case, the use of “apparent” here would become almost empty. All this needs, of course, a lot of clarification. See however [Putnam 2000]. 7A deeper analysis would probably show that such similarity might require various qualifications. 176 Aristides Baltas takes silently for granted. In other words, the ‘assumption’ that they are not belongs to the amorphous plethora of the latent grammatical condi- tions allowing the concept “cat” to make the kind of sense necessary for our employing it with confidence in the relevant inquiries as well as in all the germane language games. However, that such ‘assumptions’ are not a priori signifies that, under very particular circumstances, any one of them can become distinctly formed and ‘illuminated’, emerge from out of the background and be put to the test. It will appear then as a proper assumption (without quotes) that had been ‘unjustifiably’ and unawares taken for granted, necessitating thereby an investigation as to its war- rants. The completely baffling and totally unaccountable behaviour of some particular cats may thus indeed force us in the long run to consider an extravagant hypothesis like the above. When this happens, such an ‘assumption’ will appear ex post facto as an illegitimate pre-judgment, as a bias, as a prejudice, as an unwarranted presupposition8. In forming the latent grammatical conditions allowing the concepts involved in a scientific inquiry to make sense, these ‘assumptions’ under- write the ‘natural’ interpretation of the corresponding conceptual system (and, by means of it, everything this interpretation determines as, for instance, the sense in which the corresponding experimental transactions and their results are to be taken). More specifically, they are involved in the pictures, the analogies, the metaphors — or the intuitions — which scientists are based on in order to understand the concepts their own work produces, and to communicate their results. As such, they are not mere Wittgensteinian ladders, to be thrown away after the system is es- tablished, nor Fregean hints or elucidations (Winke), that do not belong to the conceptual system proper [Weiner 1990]. Through the work done by those ‘assumptions’, some of the connotations of those pictures, analo- gies and metaphors tarry, as indelible vestiges, on the concepts involved, forming the latent conditions of their grammaticality and the concomi- tant bounds of their meaning. In this way, while channelling the relevant investigations away from the ungrammatical, they surreptitiously close the horizon of that meaning. The leap into the ungrammatical we have been talking about and its

8These background ‘assumptions’ are not so exotic as they might appear at first sight. Although admittedly it has not placed much emphasis on them, philosophy of science has come to recognize their existence in various forms and guises: apart from Lakatos’s “hidden lemmas” that we mentioned, Bacon’s “idola”, Feyerabend’s “natural interpretations”, Laudan’s “ontological commitments”, Kuhn’s “historically changeable Kantian categories” constitute as many attempts to name the ‘assump- tions’ in question and to cope theoretically with their inescapable existence. I owe this remark to Marcello Pera. Grammatical Aspects of Radical Scientific Discovery 177 consequences can be assessed ex post facto as tantamount to the disclo- sure of precisely such an ‘assumption’ (or a set thereof) and to the effects of such a disclosure. Which is to say that an episode of radical scientific discovery observes something like the following pattern. First, a process of inquiry stumbles on a deadlock or contradiction. What confronts the scientists involved makes no real sense to them and hence they find them- selves confronting a total impasse. On the point above, we can say that, one, such a deadlock or contradiction surfaces when the grammatical bounds of the concepts involved tend to be trespassed and that, two, it is the background ‘assumptions’ implicated that silently determine these grammatical bounds, since their function is precisely to steer the process of inquiry clear of the ungrammatical. Hence it is they that silently de- termine what is a deadlock or contradiction in the given context. Given this, the second step of radical scientific discovery amounts to the illu- mination of such an ‘assumption’ and to its emergence from out of the background. Such a disclosure transgresses the bounds in question — amounting thus to a leap into the ungrammatical — and retraces accord- ingly — both widens and modifies — the grammatical space available to the inquiry. In short, an episode of radical scientific discovery turns an ‘assumption’ which, as we have said, is formlessly taken along as a mat- ter of course and to which, accordingly, questions could not be addressed (i.e. an ‘assumption’ with quotes) into a distinct proposition that can be doubted and thence conceptually and experimentally examined (i.e. a proper assumption without quotes). This proposition thus becomes open to rejection, revision, justification, and so forth9. It is these new possibilities for the development of the corresponding process of inquiry that activate the novel grammatical space opened by the radical scien- tific discovery. Thereby, the conceptual system concerned is itself not only enriched but also transformed substantially. The reason why such a disclosure transforms substantially the con- ceptual system in question resides in the fact that no scientific concept can perform its work in isolation from other scientific concepts; these are always interdependent within the system they form10. This inter-

9And not just to a simple dismissal and replacement, as would have happened, for example, in the ideological change involved in a religious conversion. This distinction opens various important issues which I cannot enter to here. 10For an account of why and in what sense scientific concepts are always interdepen- dent within the system they form see [Baltas 1988]. The effects that this ‘property’ has on the meaning of scientific concepts are presented in [Baltas 1990]. I should add that both these papers are concerned with physics. In this discipline, the interdepen- dence in question is all the more manifest because of the mathematical relations that tie physical concepts together. 178 Aristides Baltas dependence implies that background ‘assumptions’ do not perform their function in respect to one or another concept alone, for these underlie, as we have implied above, the ‘natural’ interpretation of the conceptual sys- tem as a whole. In other words, it is they that assure behind the screens the coherence and the self-consistency of the conceptual system, it is they that form the invisible grammatical glue allowing the system to be ‘natu- rally’ understood in all the mutual relations among its parts. Given this, although the deadlock or contradiction from which the process starts is always more or less centred at a particular site of the conceptual system, the effects of the illumination of the corresponding ‘assumption’ and of its emergence from out of the background are diffused throughout the system, finally leaving no concept totally unscathed. This destabilizes the conceptual system in its entirety and thereby opens radically novel and extremely pressing problems, both in respect to the coherent ar- ticulation of the concepts themselves and in respect to the empirical reality these intend to capture. The successful resolution of enough of these problems is tantamount to the establishment of a radically novel conceptual system, the one articulating the new Kuhnian paradigm. We should stress that the disclosure of such an ‘assumption’ accom- plishes, when it happens, two distinct things. On the one hand, it clears, as we have just said, novel grammatical space. As the horizon of inquiry is no longer closed by the dumb existence of this ‘assumption’, new av- enues of research are opened, new questions are asked and new answers are given, the ones, precisely, that deploy the new paradigm. On the other hand, such a disclosure creates a novel vantage point from where the preceding state of the investigation can be looked at anew. This is a vantage point whereby the anomalies whose unaccountable existence had induced the disclosure in the first place appear as misconstruals due to the work that the disclosed ‘assumption’ had been silently perform- ing. Hence reasons can be adduced post hoc for the change that has occurred, reasons that appear as correcting previous inadvertences or oversights and hence reasons that tend to assess this change as invari- ably progressive. The spontaneous whiggism of practicing scientists is based precisely on this. Let us look again at our previous examples. First, Cantor’s radi- cal scientific discovery, if looked at from the novel vantage point it itself created, appears as follows. The deadlock Cantor encountered was deter- mined as that by some background ‘assumption’ working under the time honoured conception of the part/whole relation. Within the then emerg- ing language of set theory, this relation is defined like this: a “proper subset” of a given set is one included in that set without exhausting it; Grammatical Aspects of Radical Scientific Discovery 179 a non-empty remainder is left. Thus the set, say, of even numbers is in that sense smaller, and cannot be but smaller, than the set of nat- ural numbers, since the latter includes the odd numbers as well. On the other hand, within the same language and again by definition, sets have elements, i.e. they are the sets of their elements. And another time honoured idea is that the even numbers can be put into one-to-one correspondence with the natural numbers: the even number 2n corre- sponds one-to-one to the natural number n. But then the set of even numbers has the same number of elements as the set of natural num- bers although a moment ago we demonstrated that the former is smaller than the latter and hence — how else could “smaller” be cashed in here, if it is only elements that sets can have? — it cannot but have fewer elements! Cantor’s leap into the ungrammatical, his giving a name to the ungrammatical, amounts then to his accepting this contradiction — for he cannot escape it or conceivably do otherwise — and go on defin- ing infinite sets as precisely those for which both of the contradiction’s horns hold simultaneously. The well-entrenched background ‘assump- tion’ disclosed through this move is that always and without exception, analytically so to speak, a collection of items that is smaller than another — one that forms a proper part of its corresponding whole — cannot but include fewer items. Cantor’s definition opens up the grammati- cal space where it is not necessarily the case that the relation “properly included in” coincides with the relation “has fewer elements than”: for finite sets the two relations are equivalent but for infinite sets they are not11. Giving room to this distinction — a distinction literally unthink- able before — sets up this novel grammatical space, a space wherein the old contradiction becomes automatically resolved12. The articulation of the new paradigm, i.e. Cantor’s theory of sets and what follows from there, is nothing but the exploitation of this novel grammatical space through the deployment of that distinction’s far reaching consequences. We have to note, however, that after all is said and done, after the rad- ical novelty of Cantor’s proposal has become absorbed and assimilated into the common wisdom of logicians and mathematicians, his move can appear only as simple and natural: why expect that the infinite should obey the same ‘laws’ as the finite? Post festum, but only post festum, the question is, of course, totally justified in its disarming candidness: why indeed? Second, Bohr’s radical scientific discovery, again as regarded from the new vantage point it itself created, follows the same pattern. Bohr

11I am grateful to my anonymous referee for clarifying this for me. 12Should or should not I place “resolved” in scare quotes? See note 6 above. 180 Aristides Baltas refuses to go against the physical understanding of his day by tinker- ing with the planetary model of the atom, Maxwell’s electromagnetic theory and the atom’s stability. His leap into the ungrammatical, his giving a name to the ungrammatical, amounts then to his accepting the manifest contradiction among these theories by positively decreeing that electrons rotating within atoms in their “ground state” — his name for the ungrammatical — do not radiate. And just as in the case of Cantor, this ungrammatical decree opened a novel grammatical space, the space capable of hosting a distinction literally unthinkable before, namely that between moving ‘classical’ bodies — which do emit radia- tion when following particular trajectories — and newly defined “moving quantum bodies”, that do not when following apparently similar tra- jectories. Distinguishing in this way ‘classical’ from quantum motion unavoidably puts under fire the fundamental concept of “trajectory”, leading thereby, grammatically if not historically, to the follow up dis- tinction between ‘classical’ trajectories, where position and velocity (or momentum) can be determined simultaneously with arbitrary precision, and quantum ‘trajectories’ where they cannot13. Given that “trajectory” is, by definition, the sequence in time of the determined positions and velocities (the tangents of the corresponding curve) of a moving body, this further distinction is tantamount to the disclosure and the subse- quent questioning of a quasi elemental background ‘assumption’: it is not necessarily the case, as it had been silently ‘assumed’ up to then, that the trajectories of all physical bodies do possess this, their defin- ing, property. Although this makes quantum ‘trajectories’ impossible to strictly represent in space, cloud chambers and other experimental artefacts demonstrate that the concept should not be altogether jetti- soned and hence that classical and quantum concepts bear very complex relations to one another. Concurrently, the disclosure of this ‘assump- tion’ opens the grammatical connection between quantum ‘trajectories’ and the particle/wave duality thus placing the articulation of the new paradigm of quantum mechanics well on its track. And again, after Bohr’s initial move and its various direct or indirect grammatical im- plications have become assimilated into the common wisdom of at least the practising physicists, the corresponding candid question inevitably surfaces: why expect that the exceedingly small should obey the laws governing the medium sized bodies of our everyday experience? The whole practice of teaching introductory quantum mechanics is founded on the apparent naturalness of precisely this question. Let us have a quick look at one last example. Classically speaking,

13My anonymous referee helped in this as well. Grammatical Aspects of Radical Scientific Discovery 181 the concept “wave” is defined as the propagation of a medium’s distur- bances. This is to say that, within the grammatical space supporting this definition, i.e. is within the grammatical space available to classical physics, the concept “wave” is analytically related to the existence of a material medium. To say, then, that some waves can propagate in vac- uum, i.e. in absence of the material medium whose disturbance they are, is literally inconceivable. However, speaking very roughly, the theory of relativity can be seen ex post facto as resulting from the disclosure of some of the background ‘assumptions’ silently underlying the classical concepts of motion and the concomitant postulation14 – again a name for the ungrammatical — of a new kind of entity, the electromagnetic field. This is a kind of ‘non-classical’ wave that can propagate without any material medium being disturbed, amounting thus to a ‘disturbance’ of nothing that ‘propagates’ in itself! And once again, always post fes- tum, we can repeat with both the practicing physicist and the teacher of modern physics: why expect that the exceedingly fast should obey the laws governing the kinds of motion we encounter daily?

3. Some consequences

The rough picture I have been trying to sketch has consequences. For our present concerns and to my view at least, most noteworthy are those permitting us to have another look at the insights opened up by Kuhn’s work. With the help of some clarifications and modifications, practically all of them can be rescued from most of the charges that had been besieging them from the very beginning. As a result, the guiding ideas of rationality and of scientific progress, ideas Kuhn never wanted to abandon, can be salvaged in ways that may be philosophically sound while agreeable to practicing scientists. First, from the psychological point of view, the disclosure of a back- ground ‘assumption’ does amount, as Kuhn would have it, to a “Eureka!” experience inducing a gestalt shift, a shift making one see the world un- der a new light. However here we have to be careful. Given that the main ingredients of paradigms cannot but be ideas, Kuhn’s maintain- ing that people residing in different paradigms “live in different worlds” seems to imply that it is ideas in general that determine the world — if, pace Berkeley, it does have some kind of existence of its own — and hence are in some sense primary in respect to it. As this is the core the- sis of idealism, Kuhn has been charged, apparently with good reasons,

14Of course, this is not historically accurate. 182 Aristides Baltas for offering an idealist account of science. However, on a closer look, this charge is totally misguided. For, given the above, Kuhn’s account of paradigm change can only imply that it is the world, not only as fully independent of ideas but also as absolutely primary in respect to them, that can be the only agency responsible for Kuhnian anomalies, that is for the deadlocks or contradictions on which paradigms stumble. This is to say that it is only the world that can display, be it in such an indirect and negative way, the inadequacy of a conceptual system, the fact that such a system does not possess the resources for coping with such deadlocks or contradictions, and hence for accounting for the world in the corresponding respect. In short, it is only the world, as fully independent of the ideas articulating the various paradigms, which, by resisting them, can force us into accepting that those very ideas fall short of it and thence are subordinate to it and fully reliant upon it, for better or for worse. Ideas are at peace with the world, allowing scientific, or even naïve, realism to appear as compelling, only as long as no dire anomalies surface to exert their full pressure15. It follows that Kuhn’s position on paradigm change not only cannot be charged as idealist but, on the contrary, that it is a position vindicating with a vengeance the sovereignty of the world in respect to ideas, i.e. the absolute primacy that all forms of naturalism16 demand of it. To go on, let us look at the phenomenon Kuhn calls “communica- tion breakdown”. On the present view, communication between scien- tists invariably breaks down in the relevant respect when these reside in succeeding paradigms. (As well as, with qualifications, in altogether different ones; but for reasons we will explicate, this need not concern us here). Why this is the case should by now be obvious. The scientist residing in the old paradigm has not undergone the pertinent “Eureka!” experience and still holds fast to the corresponding ‘assumption’, while remaining unaware that she is doing such a thing, i.e. that a questionable assumption is involved in the first place. Given the way we explicated the role and character of such an ‘assumption’, it follows that continuing to hold fast to it implies that this scientist cannot understand how it could be possibly questioned. Such questioning is literally unthinkable

15Such resistance of the world to the theories or paradigms trying to account for its various aspects should form, at least according to me, the starting point for a viable realist position, a position which, for reasons related to the above argument, I call “negative realism”. I have tried to explore this idea in [Baltas 1997]. 16This argument does not, of course, exhaust the issue of how ideas connect to the world. As I cannot enter into the matter here, I simply state that the kind of naturalism I would defend would reserve a place for what [McDowell 1996] calls “second nature”. Grammatical Aspects of Radical Scientific Discovery 183 from the old vantage point, as it would amount, for example, to the de- struction of an analytic relation between concepts, i.e. of a relation that is inconceivable otherwise. It would be like being capable of entertaining the possibility that some bachelors may indeed be not unmarried males while the concept “bachelor” is defined as meaning precisely “unmarried male”17. Accordingly, the scientist still residing in the old paradigm can literally not understand the effects of the disclosure in question and hence neither the concepts the colleague residing in the new paradigm is using nor much of her way of talking. It should be clear nevertheless that no kind of simple-mindedness is involved here. To say it provocatively, Lorentz’s, say, continuing to admit till the end that he never came to understand relativity theory may even make him more ‘rational’ than Einstein: the old man had precise well articulated reasons — logical, conceptual, empirical and historical — for clinging, even unawares, to the ‘assumptions’ assuring the meaning of the old concepts while his young colleague only made a wild leap into the ungrammatical18. That Lorentz never underwent the appropriate “Eureka!” experience in no way demonstrates some kind of intellectual inferiority. Lest the above be misunderstood, we should stress that the com- munication breakdown under consideration is no global breakdown. Al- though, as we have said above, the grammatical change induced by the ungrammatical leap rebounds to a greater or lesser extent throughout the old conceptual system, the two parties continue sharing the enormous grammatical space of their common language (Latin, Italian, German or whatever) within which the blind spots of their communication can be circumscribed, even if very hazily. For example, both parties can agree that explaining phenomena is what they are after while remaining completely at odds, not only on what such explanations should exactly amount to, but also on which are the phenomena to be explained19.

17For a discussion of analyticity that may shed more light on this argument, see [Putnam 2000]. 18This does not render Einstein’s move irrational per se. It can be perceived as a wild, since ungrammatical, conjecture perhaps worthy of exploration, i.e. as an extremely far-fetched promise for advancing the investigation beyond the obstacles encountered that can be justified retrospectively from its ex post facto results. As it will become clearer below, the specifics of such ex post facto justification can only lie within and be supplied by the novel grammatical space as opened by the leap in question. In the terms of the political metaphor proposed by Kuhn, the jurisprudence governing such justification is the one established by post revolutionary law. Lorentz and all those still in the grips of the old regime refuse to submit themselves to such jurisprudence, for they literally don’t understand it. 19The communication gap between Galileo and the Aristotelians, or even that between Frege and Hilbert on what a mathematical definition should amount to, are 184 Aristides Baltas

We should add that the communication situation is not totally hope- less even in respect to such ‘dialogues’. Since the disclosure of a back- ground ‘assumption’ creates, as we have said, a novel vantage point whereby one can see what prevented this new way of looking before, one is armed with important rhetorical ammunition20. Although such ammunition cannot compel logically those holding the old paradigm to undergo the pertinent “Eureka!” experience, it can serve to surround, so to speak, the corresponding background ‘assumption’ so as to force those opponents to realize, at least indirectly and in the long run, that they are unwittingly harbouring unwarranted biases. (Unwarranted, of course, from the point of view of the new paradigm). This is, I believe, the logical, or rather grammatical, niche of Galileo’s “propaganda” and of most scientists’ rhetoric and this, pace Feyerabend, is the way the ra- tional import of this propaganda and of this rhetoric should be assessed. Our pedagogical practices when we are teaching counterintuitive theories do bear an eloquent witness to the need for exerting such violence. The next point we should note is that the relation between the two succeeding paradigms is not symmetrical, and this in many senses. For one, it is not grammatically, and hence epistemically, indifferent within which paradigm one resides. Since the grammatical space available to the new paradigm includes the possibility of examining (of negating, of modifying of accepting, etc) an additional assumption unavailable to the old, namely the one resulting from the disclosure of the ‘assumption’ that had been silently taken for granted, it is a grammatical space objectively (i.e. independently of the relevant beliefs and convictions) wider than that available to the old paradigm. It should be clear, however, that this does not imply either that the new paradigm has unearthed all the background ‘assumptions’ of the old or that it does not carry background ‘assumptions’ of its own. The con- cepts the new paradigm invariably introduces cannot be understood and function in absence of their own proper background. Nonetheless, this cannot make the horizon of inquiry accessible to the new paradigm nar- rower than that accessible to the old. The newly introduced background ‘assumptions’ simply have to silently coalesce with the still undisclosed old to assure the coherent and self-consistent overall interpretation of the new conceptual system as well as to ground the understanding that an ungrammatical leap had been involved and what its upshot was. It follows that some of the undisclosed old ‘assumptions’ may be covered up more and hence their entrenchment become strengthened. But this cases in point. 20See, for example, [Pera 1994]. Grammatical Aspects of Radical Scientific Discovery 185 need not impair the future success of the new paradigm; it may only render objectively more difficult the next possible paradigm change. In any case, it is crucial to underline that the assessment of an objec- tively greater width is possible only from the vantage point determined by the new paradigm. Those clinging to the old continue to be un- wittingly constrained by the background ‘assumption’ in question, to remain blind to the possibility of its interpellation and, therefore, inca- pable of surveying the greater width attained. Accordingly, if we keep Kuhn’s metaphor of the “gestalt switch”, we should be careful to note that, unlike the duck/rabbit case and at least thus far in our discussion, this is not a switch that allows one to go back and forth. It is a semi- conducting switch, directing from the old paradigm to the new through the relevant “Eureka!” experience. This is to elaborate the asymmetry we noted above: if we continue residing within the old paradigm, we are blocked in our understanding at least parts of what our interlocutors are talking about. In fact we even consider what they are telling us as literally incomprehensible, since ungrammatical. If we reside within the new paradigm, we can understand both what our interlocutors are talking about and why they are talking this way. We are not blocked because, to go one step further, the grammatical space available to us can accommodate an explicit interpretation in our terms of the old con- ceptual system as a whole, an interpretation concomitant with the rein- terpretation of the empirical phenomena involved. In the case of post Galilean physics, where a mathematical structure always underpins the physical conceptual system thus rendering concepts and conceptual rela- tions more precise, the interpretation in question is based on an explicit, although imperfect, translation of at least a crucial part of the old concep- tual system in the terms of the new21. The case of mathematics, where no empirical phenomena are involved, should be treated separately and will not concern us in the remainder of the paper22.

21Two remarks are in order. 1. I am aware that I am mixing up “translation” and “interpretation” here against Kuhn’s careful distinction of the two terms in his [Kuhn 1983a]. My reasons for doing this will be clarified below. 2. My formulation seems to imply that, to the extent that phenomena become ‘merely’ reinterpreted across paradigm change, they, pace Kuhn, remain per se invariant. I will try arguing below why this implication need not follow although the kind of continuity suggested by my formulation seems to me inescapable. 22However I do believe that some of what follows can, with qualifications, concern mathematics as well. In any case, the irreducible differences in question imply that, for tackling adequately scientific discovery and all the associated issues, it is necessary to assess carefully the characteristics of each different scientific discipline separately and not deal with science indistinctly in the more or less standard general terms. Although I cannot enter into the matter here, I presume referring the interested 186 Aristides Baltas

What I mean can be spelled out as follows. In the passage from the old paradigm to the new, what first23 opens up is the grammatical space tied to the particular concepts located at the core of the deadlock or con- tradiction on which the old paradigm stumbled in the first place (“proper part”, “rotating charged body”, “trajectory”, “wave” and so forth). This opening up blows up and changes dramatically the meaning of these concepts. Some of them may become fully discarded (as phlogiston or caloric) while some others acquire a radically new meaning, even as their names, and for good reasons as we will see, remain the same. The novel grammatical space is such, however, that three closely connected things become possible within it. First, one can understand on its basis the role the disclosed ‘assumption’ had been playing in assuring the coher- ence and self-consistency of the old conceptual system. Thereby that old system can be interpreted in a way making clear the reasons for both its successes and failures in accounting for the empirical phenomena in its domain. Second and concurrently, the novel grammatical space can host a reinterpretation in the new language of the empirical phenomena that had been countenanced, and as they had been countenanced, by the old24. The relevant parts and aspects of nature are being under- stood now in the terms of the new conceptual system and of the novel grammatical space supporting it. Third, the new conceptual system can account successfully for at least some aspects of at least some of the phenomena (as reinterpreted) that were at the heart of the deadlock or contradiction from which the whole process started — i.e. those that the old conceptual system found impossible to handle — as well as for at least some aspects of at least some phenomena (as reinterpreted) that had been considered up to then as being successfully accounted for by the old conceptual system. To see what is involved, let us concentrate on the case of physics. For post Galilean physics, then, we can detail the above by adding that, when more or less strictly specifiable limit conditions are satisfied, some crucial concepts coming out of the ungrammatical leap appear as almost identical to the old and hence they can be considered as their (imper- fect) translations into the new language. Within the novel grammatical space, we can then talk of, say, “classical angular momentum” (if Plank’s constant tends to zero) or “classical mass” (if the speed of light tends to reader to my paper “Physics as Self-Historiography in Actu: Identity Conditions for the Discipline”, still in progress but available as a draft on request. 23Not necessarily in the temporal or historical sense. We will comment on this distinction in the conclusion of the paper. 24The continuity at issue here, mentioned in note 21, will be discussed shortly. Grammatical Aspects of Radical Scientific Discovery 187 infinity) as limiting cases of the corresponding quantum or relativity con- cepts and therefore as special cases, distinct in this sense from the gen- eral ones. Concurrently, within the novel grammatical space, appropriate conceptual relations can be produced which, under exactly the same limit conditions, appear as almost identical to some crucial old relations and hence as their translations into the new language. (Conservation laws are a case in point)25. This (imperfect) translation, together with the attendant reinterpretation of empirical phenomena in the new language, allows us to see why the old conceptual system failed in accounting for the phenomena involved in the corresponding deadlock or contradiction — these (as reinterpreted) did not and could not satisfy the limit condi- tions — as well as why it can be still considered as having succeeded, for all practical purposes, in accounting for some other phenomena — these (as reinterpreted) did satisfy, if only imperfectly, the limit conditions. At the same time, the new conceptual system is in a position to account successfully in its own terms for both these categories of phenomena (as reinterpreted), or at least for some crucial aspects thereof. We should add that, in disciplines other than physics, where mathematics does not play such a constitutive role, this ‘relation’ between the two conceptual systems might not be capable of pinning down precise translation condi- tions of concepts and conceptual relations, failing to situate determinate correspondents even for its key terms. (Phlogiston has no counterpart in post Lavoisier chemistry). Nonetheless, if we are to talk of the change in grammatical space at issue, the interpretation, at least, of the old con- ceptual system as a whole, together with the concurrent reinterpretation of phenomena, should be assured in one way or another. Whatever the case might be, we should emphasize that such a trans- lation can be only imperfect. As we have said, practically all the systemic connections within the old conceptual system are variously accountable to the ‘assumption’ disclosed through the passage of the old paradigm to the new; hence the elimination of the grammatical glue among the old concepts — as we have characterized the ‘assumption’ in question — makes the new conceptual system independent of the old in a way allowing it to develop on its own, without being compelled to espouse all the concerns of the old, to follow strictly on its tracks or even to provide translations or determinate counterparts at all for its particular parts and facets. Thus not all old concepts and relations may or need

25Such passage to the limit need not carry along, and hence need not preserve, the conceptual structure implicated; the existence of a mathematical limit does not imply a conceptually well-defined relation between the general case and the limit case. 188 Aristides Baltas

find a correspondent in the new conceptual system26 while not all parts of the new conceptual system may or need find opposite numbers in the old27. In the case of physics, not all concepts and conceptual relations of the new system may or need possess mathematical limits that appear as identical to some of the old28. In that particular discipline, even the limit cases of the new concepts and relations that do appear as identical to the old may not or need not be strict translations, for the overall conceptual structure is standardly very different29. In other disciplines, where determinate correspondents can be lacking, the imperfection in translation may be so serious that the very meaning of the term fades out in favour of interpretation. In such cases translation cannot properly be said to exist30. At any rate, the required existence of the interpretation/translation at issue adds another dimension to the asymmetry we are discussing. That the grammatical space available to the new paradigm is objec- tively wider than that available to the old implies that only the interpre- tation/translation of the old conceptual system into the language of the new is possible while the reverse interpretation/translation is blocked. The new concepts of “angular momentum” or of “mass” can accommo- date as limiting cases classical angular momentum and mass once the latter are (imperfectly) translated into the new language while relativis- tic or quantum concepts and relations cannot be interpreted/translated into the language of classical mechanics, for the work performed by the yet undisclosed ‘assumptions’ makes such an interpretation/translation literally unthinkable. In the same vein, modern chemistry would be un- thinkable for Priestley while within the grammatical space available to it we can interpret phlogiston theory in a manner allowing us to under- stand fully its conceptual structure and hence the reasons for both its successes and its failures.

26These amount more or less to “Kuhnian losses”. 27For example, oxygen can have no possible counterpart in the language of phlo- giston theory. 28For example, quantum mechanical spin has no classical counterpart and the re- lation E=mc2 cannot possess a classical limit. 29For example, Plank’s constant tending to zero can have no effect at all on the underlying structure of quantum mechanics, namely Hilbert space vectors and op- erators, while the low velocity limit of relativity theory cannot but preserve the conceptual interdependence of space and time. Both this underlying structure and that conceptual interdependence are unthinkable within classical mechanics as such. 30The conceptual structure of phlogiston theory is very different from that of mod- ern chemistry and cannot be accommodated as such within the grammatical space supporting the latter. This is also the case for caloric theory in respect to classical thermodynamics. Grammatical Aspects of Radical Scientific Discovery 189

Let us turn now, as we have promised, to the issue of continuity across paradigm change, i.e. what we had been envisaging when we decided to confine our discussion to succeeding and not generally dif- ferent paradigms. We start by stating explicitly what we have already implied, namely that a kind of continuity is assured between two suc- ceeding paradigms by the fact that the passage from the old paradigm to the new occurs on the basis of a deadlock or contradiction implicat- ing some particular phenomena. We can identify two closely connected grounds at the root of such continuity. First, and by definition so to speak, the new paradigm resolves the Kuhnian anomaly these phenomena exhibit; it is precisely this feat that provides the initial fuel required for the new paradigm to proceed with its deployment. But as we have said early in our discussion, the cor- responding novel grammatical space becomes instituted by the act of repressing the memory of a grammatical impossibility, that encountered by the old conceptual system in trying to account for the phenomena in question. Giving a name to the ungrammatical by means of a novel positive definition amounts precisely to this. This is also to say, however, that the novel grammatical space continues to enfold the same impossi- bility within it, if only in the guise of that repressed memory. And the survival of this impossibility, even in merely that guise, keeps the novel grammatical space linked to the old, thus rendering it continuous with it in that sense. What I mean is the following. We saw in our examples31 that the con- cept positively defined by the ungrammatical leap can host, directly or indirectly, a distinction between itself and the interpretation/translation of some old concept located at the core of the deadlock or contradiction at issue. That the old concept has to be interpreted/translated for be- coming thus accommodated is a direct consequence of its impossibility of overstepping the corresponding grammatical bounds. Thus this inter- pretation/translation, in being precisely an interpretation/translation, retains the memory of this impossibility. But the fact that the posi- tive definition in question institutes a novel grammatical space, wherein the ensuing new concept functions fully grammatically in tandem with the interpretation/translation of the old, makes the ungrammaticality disappear from sight and represses its memory32.

31As it can be readily ascertained, what follows applies mutatis mutandis to dis- ciplines where no direct counterparts are available and hence no translation can be properly said to exist. 32It follows that this ungrammaticality becomes eventually forgotten, fully covered under what the resultant grammatical space starts compelling everyone to take for 190 Aristides Baltas

Now, repressing the memory of this impossibility goes hand in hand with the reinterpretation of the implicated phenomena by the new con- ceptual system in the terms of the novel grammatical space. But in what way is this a reinterpretation of the phenomena exhibiting the Kuhnian anomaly? If we don’t raise the issue we cannot but be silently assuming that these are merely reinterpreted and thus that they retain as such their identity, which inevitably begs the question. To answer, we repeat that, on our account, the appearance of a deadlock or contradiction in respect to some phenomena means only that the world manifests its re- sistance to the conceptual system intending to capture them. This is to say, first, that it is the force of this resistance that the ungrammatical leap has to overcome and, second, that the success of the leap appeases this resistance by making the new conceptual system conform to the world in the relevant respect. But this can only mean that ‘something’ of the world, ‘something’ of the materiality of the phenomena concerned, is carried invariant across the leap33. For, appeasing such resistance and making the new conceptual system conform to the world can only mean that this new system manages to capture adequately the very same ‘something’ that resisted its capture by the old conceptual system. In other words, the same ‘something’ is being conceptualised in the terms of an inadequate system at one of the leap’s ends and in the terms of a correspondingly adequate one at the other end34. The novel grammati- cal space is itself stamped by the persistence of this ‘something’: the fact that what is at issue is an impossibility having concerned the phenom- granted. Thus, in the long run, the achievements of the superseded paradigm appear retrospectively as trivial, as obviously mistaken or as fully incomprehensible. It is then up to the historian of science to reveal the revolutionary character of the corresponding ungrammatical leap and to dispense intellectual justice. 33This is the ‘something’ that any brand of naturalism would minimally require, if the world is to be independent of ideas and primary in respect to them. For an argument why this ‘something’ need not amount to a Kantian “thing in itself”, even if it cannot be described or formulated by any conceptual system at all, see [Baltas 1997]. 34I should note that no “convergence to the truth” is implied by such a passage from the inadequate to the adequate. As we will explicate below, a kind of progress may indeed be involved, but it amounts only to a relation between two grammatical spaces while the world remains, so to speak, gravely silent in the background, permanently refusing to pronounce itself otherwise than through resisting inadequate conceptual systems. This is to say that, as concerns the world, the kind of progress involved is ‘negative’: the new conceptual system merely shows that the world in the relevant respect is not in fact as the old system takes it to be. And that is that. The novel grammatical space inevitably carries background ‘assumptions’ of its own that another, perhaps much more radical, ungrammatical leap may eventually disclose, showing thereby that the new conceptual system too is grossly inadequate. For more details see below as well as [Baltas 1997]. Grammatical Aspects of Radical Scientific Discovery 191 ena exhibiting the anomaly, an impossibility, moreover, that continues to survive — even only as a repressed memory — within the grammatical space having overcome the resistance they had exhibited marks precisely the elusive passage of the same ‘something’ across the ungrammatical leap. We can add that the fact that this ‘something’ remains invariant is faithfully reflected in the pertinent “Eureka!” experience, for this is an experience that cannot engage but a single thing at both its ends: after having undergone it, we understand exactly what we were incapable of understanding before. In one word, it is the invariance of this ‘something’ across that leap that allows maintaining that the new conceptual system indeed reinterprets the phenomena exhibiting the Kuhnian anomaly. To sum up our first point, we can say the following. By construction, the grammatical space of the new paradigm enfolds the impossibility of the old to handle the Kuhnian anomaly and that it enfolds it by re- pressing its memory. In repressing this memory, it resolves the anomaly and becomes the grammatical space of a new paradigm; but by still en- folding it, it remains linked to the old and thence continuous with it in this sense. Concurrently, the resistance of the world manifested by the anomaly becomes appeased through the reinterpretation of the phe- nomena exhibiting it in the terms of the novel grammatical space and through their becoming adequately captured by the new conceptual sys- tem. Despite the radical difference in the way they are being captured, the identity of the phenomena is preserved across the change in gram- matical space because ‘something’ of their materiality remains invariant. The simple idea that two succeeding paradigms are continuous because the new is born out of the old can be fleshed out in this way. Our second point is that the connection between the two paradigms assured by the interpretation/translation and reinterpretation we have been discussing expresses another form of such continuity. And this too is absolutely crucial: in its absence, i.e. in absence of the new paradigm’s capacity for deploying itself as connected through this inter- pretation/translation and reinterpretation with the old, the resolution of the anomaly would carry no scientific weight whatsoever; the correspond- ing leap into the ungrammatical would amount to an isolated ungram- matical definition that institutes no grammatical space, remaining thus perfectly idle. This is also to say that this continuity through interpreta- tion/translation and reinterpretation makes the phenomena captured by the old conceptual system appear as ‘at bottom’ identical with their rein- terpretation in the new system. In conjunction with our previous point, it is precisely this that makes the new paradigm, not merely different from the old, but the one that succeeds it. We can add that the grounds 192 Aristides Baltas of this continuity provide also the reasons why it is not only historically but also grammatically required that the names of the old concepts be preserved in the novel grammatical space as far as its continuity with the old calls for: these names constitute the necessary grammatical reminder of this continuity, i.e. of its inescapability, if the new paradigm is to be a paradigm at all in the above sense. We have to acknowledge that such continuity is close enough to a continuity of reference to almost compel us, together with most prac- tising scientists, to say that the two paradigms talk about the same phenomena tout court. Yet on the above this cannot be strictly correct. If, as we have said, the world manifests itself only through its resistance to our conceptual systems, then the phenomena we are considering can- not provide a firm hold to the relation of reference, at least as it is has been standardly discussed. Viewed from another angle, this is to say — as Kuhn too would have it — that no phenomena can be given to our experience and to our perception independently of the concepts cap- turing them35, for, to use received terminology, they are always, in a sense, theory laden36. In our terms, this simply means that the ‘some- thing’ of their materiality that remains invariant across paradigm change cannot be captured independently of some conceptual system or other, with all the corresponding background ‘assumptions’ inevitably entering into play and the attendant threat of an anomaly always lurking in the shadows. At any rate these remarks cannot, of course, exhaust the issue. A fuller account of the ‘something’ that persists across paradigm change is called for, an account that would spell out the continuity we have been discussing and the associated identity conditions for phenomena in a manner clarifying, precisely, the ways we refer to them. Our story thus far seems to suggest that the continuity and the identity conditions at issue should perhaps be explicated in terms of some kind of constancy of the general conceptual fabric of everyday language — for it is only in its terms that the world can be captured at all — as this works in concert with some kind of stability of experience and of perception — for it is only such stability that can allow our everyday language to func- tion at all in respect to the world. Yet the fact that, on the above, radically novel concepts can be introduced, novel grammatical spaces can become instituted while, concomitantly, our overall experience, and

35As [McDowell 1994] phrases it, the “conceptual goes all the way down”. 36For an interesting way to distinguish the conceptual from the theory-laden that is consonant with the present account and on the basis of which the continuity we are talking about can perhaps be spelled out, see [Pagondiotis 2004]. Grammatical Aspects of Radical Scientific Discovery 193 hence perhaps even our perception, can be broadened and become more sophisticated tend to show that such constancy should be somehow im- perfect and such stability should be somehow supple. Going beyond this admittedly vague pointer, however, would take us too far outside the scope of the present paper. In any case, the above entail that the continuity of succeeding para- digms through the interpretation/translation and reinterpretation we have been discussing is always a vital feature of radical scientific dis- covery, accomplishing at least two purposes. First, such continuity is essential for justifying the use of the old conceptual system when trans- latable counterparts exist or when the corresponding limit conditions are satisfied: after relativity theory and/or quantum mechanics became the reigning paradigms, classical mechanics can be used without many scien- tific or philosophical qualms (which does not mean straightforwardly or unproblematically) thanks to the continuity assuring the corresponding interpretation/translation and reinterpretation. Second, for assessing the role the disclosed ‘assumption’ had been playing within the old con- ceptual system and hence for accounting for the successes and failures of the old paradigm as well as for the coming to being of its successor. As specifically in the case of physics this translation saves — sanctions37 — as limiting cases the translatable, precisely, concepts and concep- tual relations of the old paradigm, its existence allows us to understand how that paradigm could have been successful in the relevant respects despite the role being played by the ‘assumption’ in question. Concur- rently, that not all parts of the old conceptual system are saved through this translation38 allows us to understand the ways in which the horizon of inquiry had been closed by the silent work performed by the same ‘assumption’. In particular, we can understand why the new paradigm could not have come into being without the relevant ungrammatical leap, a kind of leap, however, that preserves the continuity between the two paradigms precisely through the interpretation/translation and reinter- pretation at issue. Surreptitiously shifting this logical “without” to a temporal “before” obliterates such imperfection in translation as well as other telling differences between two succeeding paradigms and makes us perceive the old paradigm tout court — per se and as a whole — as ei- ther totally discardable or as just a limiting case of the new. As we have implied above, this misconception lies at the roots of the ways we tend

37The use of this term intends an allusion to Bachelard’s “histoire sanctionnée”. It lies outside the scope of the present paper to develop the proximity (and the differences) between the approaches of Bachelard and of Kuhn. 38Bachelard’s “histoire périmée” finds its correspondent here. 194 Aristides Baltas to teach modern physics and modern science in general while simultane- ously feeding the spontaneous whiggism of practicing scientists. To sum up, the interpretation/translation and reinterpretation manifesting and substantiating the continuity in question reveals the two aspects in which the grammatical space attached to the new paradigm is objectively wider than that attached to the old. Yet another dimension of the asymmetry we are discussing involves the consequences of this objectively greater width. For one, it is imperative to emphasize that attaining this greater width is an irreversible achievement. Once a new grammatical possibility becomes available through the disclosure of a background ‘assumption’ and once the corresponding implications become domesticated through the successes of the new paradigm, scientific reason cannot, grammati- cally if not historically, wipe out this possibility, forget its existence and act as if it were not there. Forsaking the “Eureka!” experience, retracing the steps of radical scientific discovery and making the disclosed assump- tion re-enter the amorphous background supporting grammatically the old conceptual system is obviously impossible. This is to say that the route for regaining the lost innocence, the route leading back to conceiv- ing the old concepts strictly the way they were being conceived before the disclosure, is blocked. At least part of the grammatical glue assur- ing the coherence and self-consistency of the old conceptual system has been found out and, to that extent, it has lost for good the corresponding gripping power. The two succeeding paradigms are asymmetrical also in the sense that the old paradigm has become definitively superseded. If this is indeed the way one paradigm succeeds another, then no room is left for an extra-paradigmatic vantage point, i.e. a point from where one could impartially assess the relative merits and demerits of paradigms, biased by none. As Kuhn would have it, nothing at all can be conceived outside a paradigm and as [McDowell 1994] would formu- late it, no view “from sideways on” can ever be available: we can reason only in the terms of a paradigm, on the appropriate more general under- standing of the term. But if we always find ourselves within a paradigm without the possibility of acceding to extra-paradigmatic neutral ground, it seems to follow that a paradigm is as good as any other. And if that is indeed the case, rationality receives a lethal blow while all kinds of rel- ativist positions, from social constructivism to various forms of alleged ‘post-modernism’, find a privileged soil on which to thrive: if rationality cannot be saved even within science, then it cannot be saved anywhere and hence we are free to choose the paradigm that suits best our conven- tions, our interests, or even our whims. However, this is a non sequitur Grammatical Aspects of Radical Scientific Discovery 195 and the corresponding charge is, once again, totally misguided. Once we accept that we cannot access God’s standpoint, where no latent gram- matical conditions need exist and all background ‘assumptions’ without exception lay bare to the gazing, no peril whatsoever to rationality can be forthcoming and no kind of relativism can be implied from our ac- count. Both Lorentz and Einstein can be as rational as we wish while the change from a paradigm to its successor is as rational a procedure as any in human thought and action. The catchword is what we have been repeating almost ad nauseam above: there is an inherent asymmetry between succeeding paradigms in the sense that the grammatical space available to the new paradigm is objectively wider than that available to the old. That the new paradigm supersedes definitively the old means that, after having undergone the “Eureka!” experience, we necessarily reside within the novel grammatical space with no possibility of going back and hence that no real choice between the two paradigms can be at issue. In that precise sense, objectivity need not imply neutrality in re- spect to paradigms and the attendant impartiality; their tie may appear unbreakable only from the point of view of God. But if that is the case, then our Kuhnian account appears as open to the opposite charge: do we endorse cumulative progress? The answer is no, for that the old paradigm has become definitively superseded does not imply that the new paradigm can do better than its predecessor in respect to all the (reinterpretations of the) empirical issues that the old had confronted, successfully or not, by its own standards and through its own means. After the ungrammatical leap and the initial empirical successes securing the irreversible character of the expansion in gram- matical space, the new paradigm may indeed solve the (reinterpretations of) some outstanding old puzzles, it may dissolve and completely discard through the corresponding interpretation/translation some others, or it may stumble in its efforts to solve (the reinterpretations of) some of the puzzles that the old paradigm had successfully tackled in its own terms. It may even prove the case that, apart from the inaugurating initial successes, no substantial claim of the new paradigm can survive future empirical trials or that the inaugurating successes themselves need to be reinterpreted. A new paradigm change may be called for, a paradigm change that will disclose additional background ‘assumptions’, those that will appear, ex post facto and from the resulting novel point of view, as responsible for the trouble this new paradigm had been encountering. This implies that there is no paradigm-free way to assess the successes and failures of paradigms so as to come up with the conclusion that the new paradigm performs unqualifiedly better than the old. For the 196 Aristides Baltas same reason as above, namely that God’s standpoint is unavailable, no neutral scale can exist, as the idea of cumulative progress would have it, on which to place such successes and failures, count them impartially and draw the balance. Nevertheless, progress does occur. As we have been repeating, the novel grammatical space is objectively wider and the old paradigm has become definitively superseded. Progress concomitant with radical scientific discovery amounts ‘merely’ to this. On the basis of what precedes, let us have a cursory look at the issues of theory comparison, incommensurability and theory choice as they have been more or less standardly discussed. As we have said, the novel gram- matical space can accommodate a one-way interpretation/translation of the old conceptual system allowing us to understand the role the corre- sponding disclosed ‘assumption’ had been silently playing in respect to it. This implies that we are in a position to understand fully the language of the old paradigm and thus become bilingual in the sense that Kuhn would have it, i.e. become capable of switching back to the old language and reason in its terms. In doing this, we can assess the old paradigm as indeed incommensurable with the new, again in Kuhn’s sense of the term: the interpretation/translation in question is not word for word, it need not preserve either reference or meaning, it uses approximations and circumlocutions of all sorts and kinds, it carries inevitable losses39. Hence the concepts of the old paradigm cannot be placed alongside those of the new and be compared with them through some common measure. Given this, the gestalt switch Kuhn is talking about can then be in- deed bi-directional in the corresponding sense, i.e. in allowing such a movement between the two incommensurable languages. What Kuhn does not make sufficiently clear, however, is that all this

39As we recall from note 32, once a given paradigm (say classical mechanics) has been entrenched deeply and long enough through scientific practice and many years of education, most older approaches tend to appear either as trivially simple and obvious (those sanctioned by the interpretation/translation and reinterpretation we are talking about) or as self-evidently wrong, if not fully incomprehensible (those not saved by that interpretation/translation and reinterpretation). This is to say that the historian of science has to expend a lot of intellectual effort in order to understand superseded paradigms in their own terms. This is a kind of effort that re-dis-covers, as it were, the background ‘assumptions’ at work in the old paradigm, the ‘assumptions’ whose disclosure has led to the current deeply entrenched paradigm, i.e. the one that the present day historian of science tends herself to take for granted. Arriving to understand the old paradigm in such a way constitutes, of course, a major gestalt shift of the purest kind. In his [Kuhn 1987], Kuhn describes eloquently the “Eureka!” experience and the gestalt shift he had himself undergone in respect to Aristotelian physics. And it is only fair to add that Kuhn’s “Eureka!” experience opened another kind of novel grammatical space, the one that, among many other things, provided the necessary grounds for writing the present paper. . . Grammatical Aspects of Radical Scientific Discovery 197 can happen only within the wider grammatical space irreversibly estab- lished by the disclosure of the corresponding background ‘assumption’. In this sense, there is really only one language at play, namely that sup- ported by the novel grammatical space. This is to say that bilingualism, the concomitant bi-directional gestalt switch and incommensurability ac- quire the characteristics that Kuhn and others highlight only after the old paradigm as such, i.e. as still harbouring the ‘assumption’ in question in its background, has become definitively superseded and only on the basis of the novel grammatical space. We can add that within this wider grammatical space, that ‘assumption’, by having become an assumption, can, as we have said, be explicitly negated, modified, or even accepted post hoc, depending mostly on the empirical grounds that have become available to the novel grammatical space40. Theory choice enters at this point and can enter only at this point, for, on the present account, the disclosure of a background ‘assumption’ and the corresponding paradigm change and expansion of grammatical space involve no choice at all. But once a literal choice of theory can only take place within a given gram- matical space, it is not a ‘big’ choice. It can never be a paradigm choice, if “paradigm” is taken in the sense of “disciplinary matrix”. As a choice of theory within a given grammatical space, it is choice of the sort scientists make all the time within what Kuhn calls “normal science”. Our departure from Kuhn’s account, then, boils down to our consid- ering that he is running together asymmetry and incommensurability41, as we have been discussing them. Two succeeding paradigms are asym- metrical in the sense that the grammatical space available to the new is objectively wider than that available to the old while phenomena of in- commensurability (together with the processes of theory comparison and theory choice) really appear only within the novel grammatical space on the basis of the one-way interpretation/translation we have been talking about42. But then incommensurability is not that dramatic after all, for it is in absolutely no position to support relativism or endanger (human and not Godlike) rationality.

40[Earman 1989] can formulate and assess the merits and demerits of all kinds of space-time theories, old and new, in the language of current mathematics on this basis and only on this basis. 41I pity the intrepid translator who may attempt capturing this distinction into Greek, for the Greek a-syn-metron is the exact translation, fragment by fragment, of in-con-measure! 42Earman notes, I take it, the same point: “Incommensurabilities have a way of disappearing when the initially seeming incommensurable set of propositions is fitted into an appropriately enlarged possibility set” ([Earman 1989, p.27], my emphasis). This “enlarged possibility set” is almost synonymous to what I call a “wider gram- matical space”. 198 Aristides Baltas

I could go on elaborating. But having almost exhausted the space available, I stop here hoping that the above succeeded in offering a rough idea that both the devil of relativism and the deep blue sea of whiggism43 can be avoided while maintaining firmly most, if not all, of Kuhn’s fun- damental insights. Both rationality and scientific progress can be vindi- cated at a price that is not really one. Pace Leibniz, Frege, the Vienna Circle positivists and many others, we should come to accept, and this with joy, that the groundings of our science can neither be made totally explicit nor become subsumed fully to a kind of algorithmic control. If per impossibile they could, life would be incredibly poorer.

4. To Conclude: Reservations and Qualifications

Lest the above be over-interpreted, I believe I should make explicit that I don’t want to argue that every radical scientific discovery follows nec- essarily the kind of pattern I have been trying to sketch. Although more examples can be forwarded, I believe that much more research is re- quired before advancing vast claims such as this. Such research may go along two main directions. The first concerns the overall philosophical coherence of the story I am trying to tell; this can be assessed if the present point of view becomes fleshed out and articulated in a way al- lowing it to be tested against the various questions still pestering the philosophical issue of scientific development. The second direction con- cerns a fuller reconstruction of particular episodes of radical scientific discovery along the lines I am suggesting. Such research, even if it does not demonstrate that my story is down and out incoherent, will most probably compel it to change substantially by recognizing, at the very least, telling differences in the patterns followed44. To go on, it is evident that all my examples are only summary recon- structions of particular episodes in the history of science, more or less in the spirit of Lakatos. However, history of science forms indeed a subject in its own right and cannot be reduced to a depository of self-serving examples and even less to a “set of footnotes”. Accordingly, if what I have to say is to be of some value to historians of science, it requires some important qualifications.

43Earman continues his previous remark by adding: “[N]o fear of being labelled Whigs should prevent us from taking advantage of an ‘apparatus’ that can (. . . ) provide [such a] larger possibility set”. Exactly! But, again, on the basis of the caveat that this “larger possibility set” becomes available only after the disclosure I have been talking about has effectively taken place. 44I have tried to walk some steps in that direction in [Baltas 2000]. Grammatical Aspects of Radical Scientific Discovery 199

These qualifications concern for the most part the division of labour between the philosopher and the historian of science. Their different tasks will come out more clearly if I try relate the present account with an historical study which I find particularly consonant with what I have been trying here to convey. This is a study of the development of low temperature physics published by [Gavroglu & Goudaroulis 1989]. The two authors suggest that in actual scientific practice, the dead- lock or contradiction I have been talking about (they don’t use this terminology) usually presents itself to the scientists involved through a whole set of interrelated puzzles, each of which may exhibit a different unaccountable property. The problem situation confronting those scien- tists is thus variously and complexly structured. The two authors then go on to classify such properties so as to show concretely that only one such puzzle and/or one such property is the ‘right’ one. By this they mean that it is their effective (possibly serendipitous) coming to grips with this particular puzzle and/or property that allows the scientists in- volved to proceed towards radical scientific discovery. According to the two authors, the process in question is one that leads the concepts im- plicated within the problem situation out of their initial contexts, where this “out of” is one of those terms, made famous by Derrida (who is not mentioned), that possess simultaneously two contrary meanings. On the one hand, the concepts in question come out of, in the sense that they belong to and are derived from, the context of the initial paradigm that supplies them with their established meaning. On the other hand, dur- ing the process of discovery, the same concepts come out of, in the sense that they become foreign to and get away from, this initial context while creating a new context and hence a new paradigm45. If this picture holds water, then the task of historians is to examine the particular processes that have led to the isolation of the ‘right’ puzzle and/or property and to its subsequent solution or dissolution. The task of philosophers is very different. They can start immediately from what has emerged post hoc as the ‘right’ puzzle and/or property — or even they can concoct one suiting the purposes at hand — and then try to pinpoint the background ‘assumptions’ at work which used to constitute as many latent grammatical conditions on the concepts implicated and, concomitantly, as much resistance to the problem’s solution or dissolu- tion46.

45See [Gavroglu & Goudaroulis 1989], especially pages 25 to 30. 46However, if it is a philosopher’s task to assess the role of various factors in sci- entific development, as is the case, for example, in the internalist/externalist debate, philosophers too are obliged to follow the details of a particular historical episode so 200 Aristides Baltas

The distinction between solution and dissolution should be taken seriously. It aims at distinguishing puzzles that appear totally irresolv- able but which are eventually shown to conform to the paradigm in place (superconductivity and superfluidity are excellent cases in point, for quantum mechanics proved fully capable of accommodating them) and those that resist such efforts to the end, thereby inducing the leap into the ungrammatical. The first of these are the puzzles solved and the second the puzzles dissolved. The fact, now, that in both cases the recalcitrant puzzle appears as a total deadlock or contradiction implies that there is no way of knowing beforehand whether it belongs to the first or to the second variety and hence the distinction in question can be drawn only ex post facto. This is to say that there cannot exist any definitive scheme telling scientists what to expect and to prepare accord- ingly. In all circumstances, everybody concerned is bathing within more or less the same ocean of background ‘assumptions’47, whose character is precisely such that it forbids scientists from realizing that they can start questioning them. Radical scientific discovery is so rare precisely because of this. To say it in one word, there is no definite method leading to radical scientific discovery and there is no advice that can be given to the scientists from the outside, even if one manages to muster for the purpose all philosophical ingenuity and all historical knowledge avail- able. In this respect, philosophy of science is totally powerless. The best it can do, which is already precious enough, is to throw some light on the situation after the upheaval has settled down and everything important has been set into place. On the other hand, the fact that the problem situation confronting such scientists is variously and complexly structured shows that the pro- cess of scientific discovery is no instantaneous act. For it may involve false starts of all sorts, research undertaken leading to a dead-end, telling but coincidental insights, bitter conflicts and discords, and all kinds of such things. As Kuhn puts it [Kuhn 1978, 369], “Discoveries are ex- tended processes, seldom attributable to a particular moment in time and sometimes not even to a single individual”. [Damerow, Freudenthal, McLaughlin & Renn 1992] stress exactly the same point. Their work shows convincingly that the process leading to the formulation of classi- cal mechanics was effectively such that both the ‘moment’ of discovery and its single particular instigator are impossible to isolate. No relevant text of the period and no phrase within any of these texts can be sin- as to distinguish determinative from anecdotic factors and so forth. I owe this remark to Léna Soler. 47Not necessarily the same in the strict sense. See [Baltas 2000]. 201 gled out as constituting the precise moment of the break. The precise moment in question simply does not exist. Surreptitiously, within the relevant texts and from one text to another, surely ‘something’ impor- tant is indeed taking place. Only this ‘something’ becomes recognizable as radically different from what existed before only after the ‘event’. But this ‘event’ has no assignable beginning or end. If this is a fact for The Great Revolution itself, it should sober us down. It brings with it a demand for humility that goes very much against the grain in the sense that too many practicing scientists would regard it with disfavour. To quote Kuhn again

[w]hat is at stake for them, implicitly or explicitly, is the concept of the unit discovery, a concept that will not withstand application to actual practice, but on which much of the reward system of science as well as important elements of the scientist’s conception of self are nevertheless based. [Kuhn 1978, 369].

This is a moral principle that both philosophically sophisticated history of science and historically informed philosophy of science carry to the practice of science. These twin disciplines then, although humble enough to admit that they cannot help much the effective process of scientific discovery, do have moral principles to bring to the world of science. And this is indeed a good thing for us all. 202 Néo-pragmatisme et incommensurabilité en physique∗

Michel Bitbol CREA

Résumé : On distingue trois strates interdépendantes dans les paradigmes kuhniens : le savoir-faire expérimental, le formalisme, et les engagements on- tologiques. Seul le niveau ontologique se trouve intégralement et explicitement exprimé dans le cadre du langage courant. Il semble donc qu’assimiler l’« in- commensurabilité » des paradigmes à une intraductibilité revient à esquiver une partie du problème. Afin de compenser cette apparente incomplétude, une conception néo-pragmatiste et structuraliste de la physique est développée, en l’appuyant sur les réflexions d’A. Pickering et I. Hacking. Au lieu d’être mar- ginalisé, le domaine des pratiques devient dans cette conception l’axe central où se définissent toutes les composantes de la connaissance, et où se décident toutes les questions, y compris celle de l’incommensurabilité. Abstract: Three interdependent levels are distinguished in Kuhn’s concept of paradigm: experimental know-how, formalism, and ontological commitment. The onlogical level is the only one which happens to be entirely and explicitly expressed in the framework of ordinary language. It then appears that identify- ing “incommensurability” (of paradigms) with untranslatability is tantamount to skipping part of the problem. To compensate for this incompleteness, a neo-pragmatist and structuralist view of physics is developed along the lines of A. Pickering’s and I. Hacking’s. In this conception, the domain of practice is no longer marginal. It rather becomes the central axis with respect to which every component of knowledge is defined and every question is to be discussed, including the issue of incommensurability.

∗Je remercie Léna Soler, ainsi qu’un rapporteur anonyme de Philosophia Scientiæ, pour leurs remarques pertinentes et leurs critiques constructives.

Philosophia Scientiæ, 8 (1), 2004, 203–234. 204 Michel Bitbol 1. L’incommensurabilité, entre langage et pratiques

Le concept d’incommensurabilité des paradigmes est compris avant tout comme défaut de traductibilité entre deux langues1. Ce biais linguistique se comprend si l’on identifie chaque paradigme kuhnien à un système de référents, à une ontologie (au sens de Quine) associée à une représenta- tion de la nature. Mais de toute évidence, le paradigme n’est pas que cela. Il s’y réduit rarement dans l’exercice quotidien des secteurs les plus avancés des sciences physiques, et il est bien davantage dans la philoso- phie de Kuhn lui-même. En physique, il existe une tradition résurgente de mise à l’écart des modèles et des représentations au profit de leurs structures sous-jacentes ; et corrélativement du langage au profit des mathématiques. Cette orien- tation s’est consolidée à la naissance de la mécanique quantique, lorsque les modèles corpusculaire et ondulatoire initiaux ont été non pas conci- liés, mais résorbés et surmontés, dans un ensemble qui comprend un formalisme abstrait (celui de Dirac et Von Neumann) et ses règles d’uti- lisation à des fins prédictives (l’algorithme probabiliste de Born). Elle a été systématisée plus tard par certains physiciens comme Murray Gell- Mann, qui ont préconisé, à titre de méthode universelle, de commen- cer par construire un modèle, puis d’en rejeter les éléments les plus concrets de dénomination ou de caractérisation des référents, afin d’en isoler les seules structures (habituellement des structures de Groupe de Transformations). Ce qui a masqué la portée d’un tel déplacement est que, le plus souvent, la focalisation sur les structures a été interprétée sur un mode réaliste, donnant naissance à un courant philosophique de « réalisme structural » [Ladyman 1998]. Le réalisme structural recon- duit l’idée courante qu’un paradigme véhicule avant tout une ontologie ayant sa terminologie, et que cela donne lieu à un éventuel problème de traduction avec les paradigmes antérieurs ou concurrents. Tout ce qu’il change par rapport à la conception classique des théories scientifiques est que ses entités sont identifiées au réseau formel lui-même plutôt qu’aux unités individuelles qu’on suppose habituellement reliées par lui. Mais la véritable signification de la méthode du retour aux structures va bien au-delà de celle que suggère le réalisme structural. Le principal effet con- cret de cette méthode est en effet d’isoler des squelettes théoriques aptes à opérer directement comme guides des pratiques expérimentales et de

1Dans la Structure des théories scientifiques, on relève trois variétés principales d’incommensurabilité : celle des langages ou idiolectes associés à une théorie, celle des valeurs cognitives, et celle de la perception d’expérience. Les deux dernières variétés appartiennent toutefois aussi à ce qui est directement exprimé dans un langage donné, et conditionné par lui. Néo-pragmatisme et incommensurabilité en physique 205 l’interprétation de leurs résultats, sans référence obligatoire, et encore moins exclusive, à une quelconque ontologie. Une structure est testable à travers le succès des pratiques orientées par elle, par-delà la variété concrète des modèles qu’y associent les chercheurs. La théorie, recon- duite à ses structures sous-jacentes, n’est pas une description de la na- ture dans un quelconque langage, mais un cadre prescriptif des activités et des attentes au laboratoire. On est à partir de là conduit à distinguer trois niveaux principaux d’intégration dans un paradigme :

– Le niveau des techniques, savoir-faire instrumentaux, et orienta- tions plus ou moins explicites de l’activité de recherche vers des buts de réalisation concrète ; – Le niveau des structures théoriques qui règlent les pratiques pré- cédentes et en recueillent les limitations contraignantes dans un réseau normatif ; – Le niveau des « scénarios » à teneur ontologique, qui ressemblent un peu à ces « récits d’un autre temps » qui, dans les sociétés à culture orale, offrent à la fois des aperçus de sens et des modèles de conduite. Les seules clauses de pertinence dont peuvent se prévaloir ces scénarios sont : (a) la compatibilité avec la structure légale de la théorie (qui n’implique pour autant aucune exclusivité) ; c’est- à-dire l’occupation conforme de « nœuds » ou de « liens » de cette structure par diverses « entités », (b) l’aptitude à concrétiser et à compléter le pouvoir régulateur de la structure théorique, et (c) la propension à motiver une grande variété de types d’investigations concrètes que ne suffirait pas à suggérer le seul formalisme; parfois autant de types d’investigation que de scénarios compatibles avec une structure théorique donnée.

Ces trois niveaux ne sont pas certes pas indépendants « en soi ». Ils dénotent trois degrés d’analyse réflexive sur le fonctionnement des sciences physiques. L’intérêt de les distinguer consiste à pouvoir faire usage de degrés de liberté supplémentaires par rapport au bloc para- digmatique intégré tel que l’a retenu une tradition simplificatrice de la réflexion kuhnienne. Kuhn a lui-même soutenu une définition extensive des paradigmes, qui inclut des composantes de signification bien plus larges que celles de représentations ou de systèmes de croyances intégralement verbalisés. Le paradigme comporte aussi et surtout un ensemble d’« engagements » 206 Michel Bitbol

(commitments) à intervenir de telle et telle manière dans la pratique ex- périmentale, à ne se poser que certains genres de problèmes, et à utiliser des schémas de résolution tenus pour valides. Adopter un paradigme, entrer dans le voir-comme qu’il favorise, ce n’est donc pas tant accep- ter une doctrine que s’être entraîné à agir (par la résolution d’exercices et la réalisation de travaux pratiques surveillés) d’une manière compa- tible avec sa « matrice disciplinaire ». Le paradigme, écrit Kuhn dans la Structure des révolutions scientifiques, sert « (. . .) à définir implici- tement les problèmes et méthodes légitimes d’un domaine de recherche pour des générations de praticiens » [Hoyningen-Huene 1989]2. Il oriente les gestes, les techniques, les choix d’appareillages, ainsi que les raisons d’accomplir et de construire. Il réside au moins autant dans des habitus acquis, dans des savoir-faire incarnés, que dans des thèmes explicités. Cette conception en partie pragmatique des paradigmes a d’importan- tes conséquences en termes de définition de l’incommensurabilité. Si on l’admet, l’incommensurabilité des langages et des représentations asso- ciées n’est plus strictement coextensive de l’incommensurabilité des pa- radigmes. Il suffirait, pour pouvoir désolidariser incommensurabilité des langages et incommensurabilité des paradigmes dans leur ensemble, de distinguer dans ces derniers les niveaux performatif, structuraux, et onto- logiques qui les constituent, et de leur reconnaître un degré d’autonomie plus grand que celui que leur prescrit Kuhn (même s’ils ne sauraient être rendus complètement indépendants l’un de l’autre et opèrent en synergie). Autonomie non négligeable des modèles vis-à-vis des pratiques et des lois, en premier lieu. On peut concevoir que des langages, des concepts, et des représentations soient (en partie au moins) intraduisibles terme à terme, alors qu’ils se rapportent en fait à un seul corpus structural et pratique. Par exemple, entre les contenus conceptuels de la théorie à variables cachées non-locale de Bohm et ceux de la mécanique quantique standard, il n’y a guère de règles de traduction. Mais dès qu’on descend au niveau élémentaire des prédictions de phénomènes, on s’aperçoit qu’il s’agit « en fait » (c’est-à-dire sur le plan des règles d’anticipation di- rectement articulées sur le domaine empirique) de deux réalisations du même réseau pragmatico-structural, à peine distinguées par des agré- gats de métaphores différents. La pratique d’investigation est en partie la même, bien que les discours et croyances affichées divergent. A-t-on là affaire à deux paradigmes distincts comprenant des couches élémentaires pragmatico-structurales communes (ce qu’on devrait affirmer si l’on as-

2La pagination renvoie à l’édition française. Néo-pragmatisme et incommensurabilité en physique 207 similait le paradigme au bloc intégré des habitus, des structures et des représentations) ? Ou bien doit-on dire au contraire que la mécanique Bohmienne et la mécanique quantique standard sont deux réalisations ontologiquement divergentes d’un même paradigme, ce qui correspond de près aux conceptions communes des physiciens ? La première option ne va pas sans soulever de grandes difficultés quant au trait majeur assigné, de manière quasi-définitionnelle, au para- digme : son unicité et sa stabilité. Lorsqu’on dit que les sciences fonc- tionnent de manière paradigmatique, contrairement à la métaphysique, par exemple, cela revient à dire que pendant une longue période de temps les chercheurs scientifiques s’accordent sur un noyau déterminant d’hy- pothèses et d’orientations. Pourtant, la multiplicité des représentations, des formes et des ontologies associées à une base pragmatico-structurale (partiellement) commune, est considérable, même aux époques de rela- tive prégnance de croyances partagées. Au temps de la mécanique clas- sique, par exemple, de multiples conceptions ontologiques cohabitaient ; surtout vers la seconde moitié du dix-neuvième siècle, au cours de la- quelle des modèles de milieux continus étaient soutenus à côté de la veille image atomiste, où l’énergétisme s’affirmait, et où des critiques convergentes de la notion newtonienne et leibnizienne de « force » se développaient. Vues de près, ces conceptions pouvaient sembler refléter des paradigmes distincts, d’autant plus que des variantes structurales distinctes pouvaient leur être associées (mécanique hamiltonienne, la- grangienne, Hertzienne etc.), et que des tendances divergentes dans les programmes de recherches allaient de pair (il suffit de comparer le pro- gramme discontinuiste de Boltzmann et le programme continuiste de Planck, dont la paternité de la théorie quantique est presque une ironie de l’histoire [Kuhn 1987], [Soler 1997]). Mais vu de plus loin tout cela ressemble aux variantes d’un même esprit d’investigation (un « air de famille ») qu’on pourrait nommer le paradigme classique au sens large, dans la mesure où les structures étaient à la fois mutuellement inter- déductibles et co-extensives, et où les ontologies partageaient de grands présupposés communs (ceux de l’individualité des entités et du caractère intrinsèque des propriétés n’étant pas les moindres). Ainsi semble-t-il possible de concilier, dans une certaine mesure, l’unicité de définition du paradigme avec la pluralité de ses réalisations représentationnelles. La seconde option, celle d’un seul paradigme avec diverses variantes, ne va cependant pas non plus sans susciter des questions embarras- santes. La question la plus épineuse est celle-ci : qu’est-ce qui, entre les trois niveaux distingués, définit à proprement parler le paradigme ? 208 Michel Bitbol

Considérons à nouveau le cas de la mécanique bohmienne. Sa structure légale empirique-prédictive est identique à celle de la mécanique quan- tique standard à un passage déductif près (celui de la dérivation d’une forme originale d’équation d’Hamilton-Jacobi à partir de l’équation de Schrödinger). Mais son ontologie, faite de points matériels individuali- sés en permanence et soumis à des champs, ressemble à s’y méprendre à la variante dominante de la mécanique classique. Quant à son pro- gramme de recherche, il est souvent hybride, combinant des démarches heuristiques typiquement classiques, et des descriptions quantiques, avec pour lien entre les deux l’expression inédite du « potentiel quantique » non-local. La mécanique bohmienne appartient-elle donc au paradigme quantique, au nom de son contenu empirique, ou au paradigme clas- sique, au nom de sa visée ontologique ? Plutôt que de s’embarrasser de tels dilemmes, mieux vaudrait reconnaître une part non-négligeable de latitude mutuelle aux trois principales composantes du concept-bloc de paradigme kuhnien. Et s’il y avait absolument à désigner le « cœur » de ce concept, ce serait sans doute la structure légale-prédictive, qui consti- tue les objectivités propres de la théorie, borne le champ des ontologies possibles, et règle une part importante (mais pas exhaustive, comme nous allons le préciser maintenant) des pratiques. Autonomie partielle des pratiques à l’égard des modèles et structures légales, en second lieu. On peut rencontrer des cas de divergences entre plusieurs traditions de laboratoire, entre plusieurs pratiques, alors qu’on tend à les forcer dans des langages véhiculaires, des modèles, voire des formalismes théoriques associés, essentiellement similaires. Peter Galison a donné une illustration détaillée de cette situation dans son livre Image and Logic, en signalant l’existence de deux sous-cultures expérimentales en physique moderne : celle de l’image (dans les cham- bres à bulles et autres dispositifs équivalents) et celle du dénombrement (dans des compteurs à déclenchement discret). L’une porte à établir des statistiques sur des événements disjoints, l’autre à appliquer des lois à des occurrences tenues pour individuelles : celle d’une entité micro- scopique identifiée manifestant ses « charges » par sa trajectoire dans divers champs, ou traduisant des règles de conservation par son mode de désintégration. Leur réunion autoritaire sous un seul cadre formel voire ontologique (celui de la description des entités « particules élémen- taires ») ne va pas sans artifices et paradoxes lorsqu’on conjoint l’aspect collectif de l’un à l’aspect individuel de l’autre. C’est par exemple le cas de la question des « particules indiscernables ». Si l’on conserve le concept de paradigme-bloc, ces paradoxes équivalent à l’affrontement la- tent de paradigmes concurrents ; comme si sous couvert de deux modes Néo-pragmatisme et incommensurabilité en physique 209 expérimentaux intra-paradigmatiques on avait en vérité affaire à la trace ou à l’ébauche de paradigmes distincts. Tantôt on relève la trace perfor- mative d’anciens paradigmes, la tradition de l’image étant marquée par le désir de perpétuer les représentations classiques par corpuscules et trajectoires. Tantôt on peut avoir affaire aux signes avant-coureurs per- formatifs de l’émergence d’un nouveau paradigme plus radical dans sa prise de distance vis-à-vis de la physique classique, la tradition du dénom- brement étant a priori plus ouverte, par son agnosticisme, à des boule- versements dans les représentations. On pense ici à l’idée d’une ontologie de « sortes » plutôt que d’individus, dans laquelle des cardinaux sont définis sans que des ordinaux aient pu l’être auparavant. Doit-on dire que la variété des pratiques expérimentales s’inscrit (coûte que coûte) dans un même cadre paradigmatique, ou qu’elle manifeste des signes avant- coureurs d’éclatement du paradigme ? Ici encore, plutôt que se laisser troubler par ce genre de dilemme, on est porté à assouplir et à décom- poser le concept de paradigme en plusieurs moments semi-indépendants, de chronologies évolutives différentes, et de modes d’association variés. On est en particulier amené à se demander s’il n’y a pas un fonction- nement partiellement séparé des systèmes de pratiques, avec des critères propres de cohérence ou de clôture, ainsi qu’un possible équivalent d’in- commensurabilité qui ne se traduit certes pas par l’intraductibilité de certains termes, mais par l’exclusivité mutuelle des gestes et des effets expérimentaux qui en résultent. Ces systèmes de pratiques expérimen- tales opèreraient en sous-main soit pour assurer la cohésion d’un para- digme structural en unifiant ses méthodes en réponse à des questions elles-mêmes unifiées en dépit de la variété superficielle des images et mo- dèles, soit au contraire pour instaurer, à travers leur multiplicité et leur incompatibilité, des tensions internes qui portent en germe une future révolution scientifique. Telle est l’idée que suggère la latitude mutuelle des strates consti- tutives du paradigme. Nous devons cependant l’étayer un peu avant de la développer. Il existe bien des pratiques expérimentales différentes, voire des cultures techno-instrumentales différentes dans les laboratoires, mais en quoi cela autorise-t-il à qualifier ces différences d’« incommen- surabilité », ou d’« incompatibilité » ? Perçues de l’extérieur, par un ethnologue, un greffier, ou un spectateur de laboratoire, ces pratiques ne sont effectivement que différentes. L’inventaire des comportements, du matériel et des changements observés les caractérise suffisamment, et seuls des écarts statiques, énumérables point par point, s’y manifes- tent. Perçu de l’intérieur, en revanche, par un acteur de la recherche 210 Michel Bitbol expérimentale, tout change. Chaque geste est intentionnel, porté par des présupposés et gouverné par un projet. Ce sont les présupposés et le projet de recherche qui conduisent à sélectionner les actes, à les organiser en séries disjointes excluant généralement les combinaisons et donnant une signification parfois « sans commune mesure » aux résultats obtenus. Mais cela ne revient-il pas à admettre qu’en fait, la prétendue « incom- patibilité/incommensurabilité » des pratiques ne fait que refléter celle des théories mises en jeu ? Et n’est-on pas rabattu dans ce cas sur une conception plus orthodoxement kuhnienne de l’incommensurabilité, re- posant sur la non-superposition des réseaux de problèmes posés dans chaque cadre théorique et sur les capacités divergentes qu’ils ont à y répondre ? Pas vraiment, et pour au moins deux raisons liées. A — Première raison. Les présupposés de la recherche ne se réduisent pas à ce qui est énoncé dans les théories et modèles qui leur sont asso- ciés. Ces présupposés (en principe explicitables, mais non intégralement explicités sous peine de régression à l’infini) relèvent en grande partie de ce que M. Polanyi appelait la « dimension tacite », et que J. Searle [Searle 1983] fait relever de l’« arrière-plan » de l’action. Les savoir-faire sont la condition préalable de la constitution des savoirs, et des projets trop généraux pour être déclarés comme tels (« connaître les caracté- ristiques propres de cela qui est là-devant ») sous-tendent les projets pleinement déployés dans un cadre théorique (par exemple : détermi- ner le rapport charge/masse de l’électron). Les présupposés performatifs confèrent ainsi à l’horizon de sens des pratiques une certaine capacité d’affranchissement à l’égard de ce qu’en indique la théorie. Plus généra- lement, le simple « faire » nourri de présupposés performatifs précède et excède toute tentative d’énonciation : « We don’t need the walking rule in the first place ; we just walk » [Searle 1983, 152]. Pour voir à l’œuvre cette aptitude des pratiques à s’affranchir des cadres théoriques voire du cadre linguistique, il suffit de constater que, dans l’histoire de la physique, une expérience unique, dotée de son pro- jet implicite, peut se trouver orientée vers la mise à l’épreuve de plu- sieurs théories [Galison 1987, 12], et ne devoir être que partiellement réinterprétée lors du passage de l’un des domaines théoriques à l’autre. Un indice corrélatif de l’enracinement anthropologique non-déclaré des arrière-plans performatifs, d’autant plus profond qu’il reste cryptique, est que ces arrière-plans peuvent inciter à maintenir l’interprétation des phénomènes en-deçà de ce que la théorie en vigueur rendrait accept- able sans artifice. On constate souvent des porte-à-faux entre un fonds de présuppositions tacites indispensables à la vie et à la communica- tion au laboratoire, et les contraintes qu’impose un nouveau formalisme Néo-pragmatisme et incommensurabilité en physique 211 dont le champ de validité s’étend au-delà de l’environnement quotidien et des catégories véhiculaires des expérimentateurs qui cherchent à le tester. Parmi les porte-à-faux de ce genre, ceux de la physique quan- tique sont les plus connus. De nombreux paradoxes de la physique quan- tique ne se comprennent aisément que lorsqu’on les attribue au conflit entre des présupposés performatifs de l’activité humaine toujours actifs à l’échelle mésoscopique, y compris l’activité expérimentale, et la struc- ture des prévisions fournies par la théorie. Ces paradoxes peuvent dès lors être considérés comme un signe indirect des limites de la dépendance des présupposés performatifs à l’égard du cadre théorique. B — Deuxième raison. Une méthode expérimentale, gouvernée par la Weltanschauung d’une culture, peut infléchir de manière ascendante l’orientation théorique. Une excellente illustration de ce cas est offerte par la « révolution chimique » de Lavoisier. Après s’être entourée de précautions, B. Bensaude-Vincent finit par désigner le facteur central de la révolution de Lavoisier, celui qui a commandé le basculement théo- rique plutôt qu’il n’en a été la conséquence : l’utilisation systématique, valorisée, voire exaltée de la balance [Bensaude-Vincent 1993]. C’est la réflexion sur la place déterminante de la balance et de l’acte de pesée qui la conduit à résumer : « Des pratiques instrumentales peuvent non seulement provoquer le renversement d’une doctrine, mais elles modi- fient même les normes ou exigences d’explications » [Bensaude-Vincent & Stengers 2001, 11]. Comment cela peut-il s’expliquer ? L’enjeu est ici d’identifier le vrai statut de l’instrument et des pratiques instrumentales, intermédiaire entre un instrument indifférent, source neutre de renseignements pour les partisans de diverses théories (empirisme), et un instrument dont la conception et l’usage sont déterminés par un modèle théorique suscep- tible d’une complète énonciation (version langagière de holisme gnoséolo- gique). Ni conforme au seul empirisme, ni intégralement explicable dans le cadre du holisme gnoséologique, le rôle de l’instrument acquiert en fait une importance à laquelle il ne pourrait prétendre selon aucune des deux doctrines épistémologiques précédentes. D’un côté, il faut admettre que la balance et son utilisation pour évaluer les gains et pertes de matière dans une transformation, étaient loin d’être inconnus en chimie avant Lavoisier. C’est là l’aspect empiriste du statut de l’instrument, et beau- coup d’historiens des sciences s’en sont prévalus pour minimiser son rôle dans la révolution chimique de Lavoisier. Mais d’un autre côté, Lavoisier fait acquérir à la balance une place quasi-exclusive dans son argumen- tation, dans ses pratiques quotidiennes, dans le traitement de questions qui ne relevaient pas avant lui de son utilisation. 212 Michel Bitbol

Une telle centralité acquise de l’instrument de pesée pourrait se com- prendre dans le cadre d’un holisme théorético-expérimental à dominante théorique, si l’on admettait que c’est la théorie nouvelle, avec son modèle combinatoire et ses principes de conservation, qui exige l’utilisation de la balance et en gouverne l’emploi. À l’examen, cependant, on s’aperçoit que ni l’épistémologie ni la démarche de Lavoisier ne s’accordent avec une telle forme d’a priorisme théorique. Un troisième facteur intervient chez lui en sous-main, qui n’est ni empirique ni théorique mais axio- logique. Une axiologie qui, en plus, dépasse nettement le cadre restric- tif des valeurs cognitives partagées par les membres de la communauté restreinte des chercheurs. La balance est souvent présentée par Lavoi- sier comme symbole de précision, de justice, de mesure en un sens non seulement métrique mais éthique. Et c’est en s’appuyant sur cette sur- valorisation culturelle (le plus souvent tacite, mais inscrite en filigrane dans le caractère sans appel des affirmations et des choix) que les ré- sultats en provenance de la balance acquièrent leur force de conviction rhétorique, devant les académies et dans les publications. La théorie est dès lors tenue de rendre raison en priorité, si ce n’est exclusivement, des données en provenance de la pesée (acte de haute portée symbolique, à cette époque de réflexion radicale sur la légitimité des pouvoirs), et toutes les catégories théoriques sont élaborées en conséquence. Au lieu de rester une simple ressource informative parmi d’autres, la balance (avec ses pratiques associées) est devenue une norme épistémologique. Son usage exclusif, commandé par une valeur de grande extension cultu- relle, a imposé une marque décisive à la théorie dont le développement est conditionné par cette culture. On commence à comprendre à partir de là qu’il puisse y avoir « in- compatibilité/ incommensurabilité » des pratiques, de manière relative- ment indépendante de l’incompatibilité/ incommensurabilité des conte- nus théoriques. Cette sorte d’incompatibilité bien à elles leur vient de l’incompatibilité des arrière-plans de valeurs qui les gouvernent (et qui ne s’identifient pas forcément à celles qui gouvernent l’édifice théorique). Par ricochet, la forme restreinte d’« incommensurabilité » qui concerne les pratiques peut induire une part d’« incommensurabilité » entre une théorie qui prend une certaine activité expérimentale pour référence mé- thodologique, et une autre théorie dont l’activité expérimentale de réfé- rence est différente. Etudier le rôle que jouent les pratiques de laboratoire me semble donc un complément indispensable à l’analyse fine et détaillée du langage méta-scientifique dans l’analyse de la question de l’incommensurabilité. Cela ne ferait après tout que réactiver le contenu métaphorique du terme Néo-pragmatisme et incommensurabilité en physique 213 même d’incommensurabilité : absence d’une commune mesure ; absence de procédure d’étalonnage commun par rapport à laquelle comparer des séries disjointes de phénomènes apparaissant dans des conditions elles- mêmes disjointes. Afin d’amorcer cette étude des pratiques de laboratoire, je prendrai pour fil directeur la démarche d’Andrew Pickering, quitte à la discuter chemin faisant. L’étape initiale du travail, dans la section 2 qui suit, consistera à mon- trer comment les pratiques expérimentales peuvent être tenues pour le pi- vot du travail scientifique, par-delà l’habituel face-à-face entre leurs pro- duits (les phénomènes) et leurs motivations (les assertions théoriques). Il deviendra à partir de là vraisemblable que le facteur d’incommensu- rabilité « performative » puisse acquérir une importance centrale plutôt que marginale. À la section 3, la répartition habituelle des rôles entre un sujet qui propose une théorie, et une chose-nature qui donne son verdict de va- lidité sera radicalement mise en cause. On commencera à comprendre à partir de là que s’il doit y avoir une part d’incommensurabilité entre « paradigmes », elle ne peut être ni dictée par un choix (« subjectif ») de réseaux distincts d’énoncés et de termes, ni imposée par les domaines (« objectifs ») dont il s’agit de rendre raison, mais co-produite à l’inter- face. La section 4 montrera comment concevoir cette notion de co-produc- tion : en tant que dialectique, ou boucle de rétro-action, interne au réseau des pratiques. Le propos de la section 5 est d’élargir le champ de la « sous-détermina- tion des théories scientifiques » à la plasticité des activités expérimen- tales. Cela conduira à atténuer plus encore, si besoin est, le caractère tranchant, irrémédiable à première audition, du concept d’incommensu- rabilité dans sa dimension historique. Au sein de la dynamique des acti- vités d’élaboration des connaissances, l’« incommensurabilité performa- tive » apparaîtra elle-même comme un simple instantané. La section 6 a une importance particulière pour la question de l’incom- mensurabilité, puisqu’elle vise à montrer en quoi consiste l’équivalent néo-pragmatiste du « paradigme » : un cercle auto-consistant de pra- tiques et de guidage théorique. Le caractère apparemment discontinu du passage d’un paradigme à l’autre s’explique ainsi par la nécessité de refondre entièrement un cercle de ce type afin d’atteindre à nouveau à l’auto-consistance. Enfin, la section 7 portera sur ce que je soupçonne être au cœur 214 Michel Bitbol du concept de paradigme (et, partant, des éventuelles incommensurabi- lités) : les structures formelles des théories physiques.

2. L’engrenage des pratiques

La conception d’Andrew Pickering a pris le nom suggestif d’engrenage des pratiques (traduction approximative de Mangle of Practice), parce que c’est, selon Pickering, d’un mécanisme complexe, incluant des élé- ments cognitifs, normatifs, sociaux, matériels, technologiques, interpréta- tifs, formels etc. qu’est issue ce que nous finissons par prendre pour notre durable « image du monde ». Cette approche a été formulée sans rapport apparent avec les problèmes d’interprétation soulevés par la mécanique quantique, mais, ainsi que nous allons le voir, elle s’avère éclairante dans ce domaine. L’option fondamentale de Pickering consiste à inverser le rapport tra- ditionnel entre l’idiome représentationnaliste de la théorie de la connais- sance et l’« idiome performatif » des expérimentateurs. Loin de tenir le second pour un simple auxiliaire du premier qui serait seul détenteur de vérité, il considère que le premier est dérivé du second par cristallisations ontologiques successives. Sa filiation est pragmatiste, comme le montrent ses références répétées à James et à Dewey [Pickering 1995, 179]. Le principe de sa démarche consiste à refuser de se placer d’emblée du point de vue du résultat achevé des pratiques expérimentales et concep- tuelles des chercheurs, c’est-à-dire d’un point de vue où l’on se considère autorisé à établir une distinction nette entre ce qui revient à des objets et ce qui revient à l’intervention des sujets [Latour 1997]. Au lieu de cela, on suit d’aussi près qu’on le peut le cours de ces pratiques, qui consistent indissolublement en actions-des-sujets-dans-le-réel, sans qu’une division interne à cet égrènement de termes joints par des traits d’union, ne soit possible ou même nécessaire à ce stade. Le retour au moment du surgisse- ment performatif indifférencié des sciences une fois accompli, la question qui se pose n’est plus celle de la correspondance entre des connaissances humaines et une nature extérieure pré-constituée, mais celle de la co- stabilisation dans la pratique :

(a) de processus ou objets qui puissent être traités comme s’ils étaient indépendants de cette pratique, et

(b) de contenus théoriques qui, par-delà leur valeur d’instrument pré- dictif, soient interprétables comme descriptions de ces processus ou objets. Néo-pragmatisme et incommensurabilité en physique 215

Autrement dit, on ne se demande plus comment il est possible qu’une théorie soit la représentation fidèle d’une réalité indépendante, mais com- ment s’élaborent dans l’activité des chercheurs à la fois la relation de représentation et les conditions pour que les termes de cette relation puissent être considérés séparément l’un de l’autre en fin de parcours. On ne s’inquiète plus de savoir si une correspondance existe (question de toutes manières indécidable, en raison du vieil argument du « diallèle » [Kant 1800, 54]3) mais par quel chemin performatif et adaptatif a été instaurée une situation qui permette de s’exprimer comme si il y avait correspondance. L’axe central des pratiques de la recherche est l’instrumentation ex- périmentale, ou plus largement l’ensemble des outils et des « machines » utilisés au laboratoire. Les instruments incarnent en premier lieu un pro- jet d’investigation parce qu’ils sont orientés tantôt vers la production des conditions qu’on désire explorer, tantôt vers la mesure de variables tenues pour pertinentes. Et ils représentent en deuxième lieu le site de manifes- tation des obstacles qui s’opposent au bon déroulement des plans conçus au départ parce que leur agencement laisse subsister une part incontrôlée d’où peut surgir l’inattendu. À vrai dire, ils combinent étroitement ces deux caractéristiques, car ils ne laissent transparaître les obstacles qu’à travers la grille de lecture imposée par le projet (implicite et explicite) qui a présidé à leur conception. L’instrumentation étant l’axe central des pratiques de recherche, et les pratiques de recherche étant l’axe central à partir duquel peut émerger une structure évoquant une représentation de la nature par la théorie, la question de l’incommensurabilité devrait se discuter au moins autant au niveau de cet axe central, de ses valeurs directrices et de ses présupposés sous-jacents, que de ses produits dérivés (les phénomènes, le formalisme théorique, et les engagements ontologiques).

3. Contraintes ou résistances ?

Puisque les obstacles sont informés par un projet d’action incorporé dans l’appareillage, et qu’ils surgissent seulement en réponse ordonnée à une mise en œuvre elle-même ordonnée de l’instrumentation, Pickering es- time qu’il est peu judicieux de les nommer des « contraintes ». Selon lui, en effet, le terme « contrainte » connote le caractère statique et pré- donné de l’obstacle : « le langage de la contrainte est le langage de la

3« (. . .) Puisque l’objet est hors de moi et que la connaissance est en moi, tout ce que je puis apprécier c’est si ma connaissance de l’objet s’accorde avec ma connais- sance de l’objet. Les anciens appelaient diallèle un tel cercle dans la définition ». 216 Michel Bitbol prison : les contraintes sont toujours là, exactement comme les murs de la prison, bien que nous ne nous heurtions à eux qu’occasionnelle- ment (et que nous puissions apprendre à ne jamais nous y heurter) » [Pickering 1995, 66]. Au contraire, le terme « résistance » suggère la ré- ciprocité d’une réaction répondant à l’action. L’eau de l’océan dresse par exemple une résistance à l’avancée d’un navire. La résistance de l’eau, avec sa structure directionnelle et son intensité, émerge en même temps que l’acte planifié (la progression dirigée du bateau) auquel elle s’oppose. « (. . .) On doit considérer la résistance comme authentiquement émer- gente dans le temps, à la manière d’un bloc surgissant (. . .) à l’encontre de tel ou tel moment d’une pratique orientée vers un but » [Pickering 1995, 67]. La conséquence attendue de ce changement de vocabulaire et de concepts connotés, est la diminution des tentations d’investissement on- tologique des obstacles rencontrés par la recherche. Les « contraintes » risquent d’être tenues pour quelque chose qui existe déjà, qui est pré- formé de toute éternité dans les objets visés par les chercheurs, et que les théories scientifiques ont à découvrir puis à représenter. Au contraire, les « résistances » sont structurées par la pratique ; elles ne sont dues ni exclusivement au milieu exploré ni exclusivement au projet d’exploration mis en oeuvre mais au concours (a priori indémêlable) des deux termes. Ici, ce qui se voit hypothétiquement attribuer l’antécédence nécessaire pour être ontologisé (le « milieu »), n’est pas supposé posséder de lui- même les structures qui se prêtent à la représentation. Inversement, les structures qui surgissent en réaction à une activité ordonnée, et qui sont pour leur part représentables, ne sont pas supposées avoir le degré d’in- dépendance qui leur confèrerait une dignité « Ontologique » au sens le plus fort, pré-quinien, de ce terme. I. Hacking, qui soutient également, au vocabulaire près, ce passage des « contraintes » aux « résistances », en donne une formulation vo- lontairement provocatrice : les chercheurs scientifiques n’expliquent pas tant, selon lui, les phénomènes, qu’ils ne les « créent » par leur activité d’investigation [Hacking 1983, 355]. Le problème est qu’une fois cette thèse très forte affirmée, I. Hacking se trouve conduit à des aménage- ments, à des reculs partiels, et à des concessions (peut-être excessives). Tout d’abord, Hacking considère qu’il y a quelques exceptions à cette thèse générale de la « création » des phénomènes reproductibles dont doivent rendre compte les théories scientifiques. L’une d’entre elles est (évidemment, a-t-on envie de dire) celle des phénomènes astronomiques. Cette exception ne fait cependant, commente Hacking, que confirmer indirectement la règle par le fait même de sa rareté : il serait difficile Néo-pragmatisme et incommensurabilité en physique 217 de trouver ailleurs qu’en astronomie d’authentiques phénomènes repro- ductibles pré-existants. Par ailleurs, pour ce qui est des phénomènes ou « effets » obtenus au laboratoire (comme l’« effet Hall » ou l’« effet Josephson »), I. Hacking admet qu’ils ne sont pas vraiment créés de toutes pièces mais simplement isolés et purifiés à partir d’un devenir naturel complexe. L’idée courante selon laquelle les « effets » attendaient tels quels dans la nature qu’on les découvre, provient selon lui d’une distorsion imposée par une relecture théorique a posteriori, une fois leur procédure d’isolement achevée. Car c’est seulement si l’on se fie à cette relecture qu’on est tenté de croire que la complexité du devenir naturel résulte d’une composition des divers « phénomènes » ou « effets », au lieu de reconnaître qu’à l’inverse c’est par une procédure de dé-composition menée à bien au sein du flux naturel qu’on est parvenu à y circonscrire des « phénomènes » ou « effets ». Telles sont les deux concessions consenties par Hacking à l’affirmation courante d’une pré-existence des phénomènes dans la nature. Si l’on y regarde de près, cependant, on s’aperçoit que leur importance aurait pu être réduite à condition d’aller jusqu’au bout des perspectives ouvertes par les sciences cognitives et la physique moderne. En premier lieu, l’idée d’une pré-donation des « phénomènes » ou régularités astronomiques ne semble aller de soi que parce que les condi- tions de leur constitution sont banales ; trop banales pour qu’on y prête attention. Afin qu’émergent des régularités sidérales, il faut s’être au- paravant donné les moyens de réidentifier des corps célestes, à travers la succession des jours et des nuits, ou avant et après leur occultation par des nuages. Il faut aussi, dès qu’on les a réidentifiés, les suivre percep- tivement (ou à l’aide de détecteurs et de procédures de traçage angulaire automatique) le long de leur trajectoire ; il faut repérer leurs positions relatives et les variations de ces positions relatives ; il faut pour cela organiser des systèmes de coordonnées appropriés. Sans ces procédures de réidentification, de traque, et de repérage mutuel, pas de régularité et donc pas de « phénomène » astronomique à « sauver » par quelque « système du monde » que ce soit. La seule raison qui semble justifier qu’on passe sous silence cette activité de constitution des phénomènes astronomiques est qu’elle est en grande partie isomorphe, avec un degré de systématicité en plus, à l’activité de constitution des « événements » et des « choses » de l’environnement familier. Cette dernière allant de soi, du moins avant qu’on se soit heurté à la difficulté de la reproduire par des procédés d’intelligence artificielle, rien n’obligeait à l’expliciter parmi les préalables nécessaires à la définition des phénomènes astronomiques. Plutôt que de la pré-donation des phénomènes astronomiques, il faudrait 218 Michel Bitbol donc parler de leur pré-constitution par le biais de couches d’activités qui anticipent l’œuvre scientifique. En second lieu, l’image d’une simple dé-composition de la complex- ité naturelle en faisceaux d’« effets » produits au laboratoire, est très en retrait par rapport à la conception du phénomène qu’on a été con- duit à adopter en mécanique quantique4. Selon Bohr, par exemple, non seulement le phénomène n’est pas quelque chose qu’on puisse traiter comme s’il survenait spontanément dans la nature, mais il n’est même pas quelque chose qu’on pourrait séparer du devenir naturel par un procédé volontaire d’analyse. L’instrumentation expérimentale ne joue pas seulement chez lui le rôle d’un moyen permettant de mettre en évi- dence ou d’isoler des phénomènes déjà disponibles ; elle participe indis- solublement à leur définition par son architecture, voire à leur produc- tion par ses phases singulières de fonctionnement à la fois incontrôlables et irréversibles5. Au demeurant, sauf à avoir recours à des « variables cachées », le formalisme quantique ne se laisse pas interpréter comme description d’occurrences survenant d’elles-mêmes (aussi enchevêtrées soient-elles) au sein du milieu naturel microscopique [Bitbol 1996]. En raison du « principe de superposition », ce que le phénomène comporte de détermination, c’est-à-dire de stricte opposition à l’égard d’une liste donnée d’autres phénomènes possibles, n’a en effet aucune contrepartie

4Il est vrai que cette image semble retrouver une certaine actualité dans d’autres interprétations de la mécanique quantique, comme celles qui sont basées sur la lo- gique quantique ou les théories à variables cachées. Mais à la réflexion, ce retour s’apparente à un faux-semblant. L’échevau de processus naturels « indépendants » que les théories à variables cachées conduisent à se représenter reste, de leur propre aveu, principiellement hors d’atteinte de l’expérience ; et ce qui est accessible à l’expé- rience est un phénomène « contextualiste » qui fait intervenir, de façon inanalysable par toute expérience supplémentaire, quelque chose qui revient au processus ima- giné et quelque chose qui revient au fonctionnement de l’appareillage. Quant aux interprétations fondées sur la logique quantique, les propriétés non-booléennes dont elles peuplent la nature peuvent trop facilement être lues comme autant de pro- jections ontologiques de phénomènes relatifs à des contextes instrumentaux parfois incompatibles. Cela d’autant plus qu’elles ne sont pas aussi générales que les phéno- mènes contextuels : des propriétés, fussent-elles non-booléennes, exigent un support, alors que des phénomènes ne requièrent que des circonstances d’apparition. Face aux théories quantiques des champs, qui rapportent les supports traditionnels (les « par- ticules ») à de simples valeurs entières d’observables « Nombre », une conception qui fait l’économie du concept formel de « support de propriétés » acquiert un avantage incontestable. 5La question de savoir à quelles époques de sa vie, et surtout jusqu’à quel point, Bohr s’en est tenu à cette conception strictement holistique et émergentiste du phéno- mène a été très discutée [Faye 1991, 193]. Il faut cependant reconnaître que, par-delà les conflits internes au système de priorités philosophiques de Bohr, c’était bien vers cette position que conduisaient les plus audacieuses de ses analyses. Néo-pragmatisme et incommensurabilité en physique 219 dans le symbolisme de vecteurs d’état utilisé pour prédire les résultats d’expériences portant sur une préparation de ce milieu. En résumé, la procédure expérimentale peut être dite ici « créer le phénomène » en un sens beaucoup plus fort que celui dont Hacking avait fini par se contenter à la suite de sa concession. Il reste à ce stade à affronter ce que l’expression de Hacking « créa- tion du phénomène par l’expérience » a de choquant. N’a-t-on pas ici l’impression que quelque chose de l’ordre de la décision arbitraire de l’expérimentateur est intervenu, alors même que le but des sciences est de s’en affranchir ? Il n’en est rien. Rappelons qu’en physique microsco- pique le phénomène lui-même n’est pas déterminé dans sa singularité par une décision de l’expérimentateur. Sa capacité à manifester d’éven- tuelles « résistances » reste donc intacte. Seule la gamme de possibles dont il actualise l’un des éléments dépend de la matérialisation d’un pro- jet de recherche, à travers l’utilisation de certaines pièces d’appareillage conçues et construites par une équipe d’expérimentateurs. Ce projet n’a par ailleurs lui-même rien d’arbitraire ; il s’inscrit dans le prolongement méthodique d’une histoire du processus de recherche que les nombreuses « résistances » rencontrées dans le passé n’ont pas manqué d’infléchir. Ceci étant acquis, nous sommes conduits à retourner notre attention vers l’origine psychologique et doctrinale du soupçon suivant lequel la conception des résistances développée par les philosophes des sciences néo-pragmatistes revient à soutenir que les faits sont « fabriqués » par le sujet expérimentateur. Un tel soupçon, courant, presque lancinant, est avant tout révélateur du cadre de pensée de ceux qui le formulent. Dans le contexte de l’alternative dualiste de la théorie de la connaissance, il est en effet naturel de considérer que si le phénomène isolé et « mis en évidence » par l’expérience ne peut pas être reconduit à l’objet, et à l’objet seul, c’est parce que le sujet l’a altéré ou fabriqué à lui seul. Mais dans le cadre d’une conception émergentiste, la perspective change du tout au tout : la stricte répartition des tâches entre un objet stabilisé et un sujet cognitif et social apte à le décrire est ici un aboutissement souhaité de l’entreprise d’investigation plutôt qu’une donnée de départ. Ni attribuable isolément à l’objet, ni fabriqué en partie ou en totalité par le sujet, le phénomène surgit à l’intérieur d’un processus intriqué qui permettra peut-être plus tard de mettre à part ce qui revient à des « objets », à des « instruments », et à des « orientations individuelles et sociales ». Dans sa discussion du concept de paradigme, Kuhn s’approche de la thèse émergentiste, mais demeure souvent en-deçà d’elle par l’évocation répétée d’une dualité quasi-kantienne entre l’équivalent de la chose en soi 220 Michel Bitbol et l’équivalent des formes a priori de la sensibilité et de l’entendement. S’il admet que « (. . .) les sujets épistémiques sont co-constitutifs (d’un) monde (. . .) », c’est uniquement au sens où ils imposent leur regard, leur façon de percevoir, à une nature « intouchée et non-influencée par les changements révolutionnaires dans les sciences » [Hoyningen-Huene 1989, 33]6. Dès lors, l’incommensurabilité a toutes les chances de rester confinée au niveau des structures perceptives collectives, subjectives au sens large, et de ne pas vraiment concerner le continuum naturel. Elle dénote un cadre durable d’attentes perceptives. À l’inverse, des partisans d’un relativisme ontologique, comme N. Cartwright, pourraient affirmer que l’incommensurabilité est celle des régions du monde elles-mêmes, d’un monde intrinsèquement « tacheté » [Cartwright 1999], et non pas celle des sujets qui les perçoivent. Mais si l’on se garde de cette conces- sion au dualisme, la question de savoir lequel des deux pôles du processus épistémique est en permanence concerné par l’incommensurabilité perd tout son sens. Née dans le processus qui conduit à définir des domaines et objets d’étude, au sein de l’axe central des pratiques, l’incommensu- rabilité des catégories organisatrices peut se voir tour à tour projetée sur le sujet ou sur le monde sans que cette projection ait la moindre portée métaphysique.

4. L’accommodation, au sens technique aussi bien que théorique

Le travail scientifique progresse, rappelle Pickering, à travers une dia- lectique des résistances et de l’accommodation à ces résistances [Picke- ring 1995, 22]. Pour comprendre la complexité d’une telle dialectique, il faut commencer par rappeler que les résistances se manifestent en tant qu’écarts à ce qui était attendu dans le cadre d’un projet général impliquant à la fois : des valeurs cognitives et éthiques, des préjugés mé- taphysiques thématisés ou latents, les circonstances sociales, culturelles, historiques, ou économiques qui favorisent ces valeurs et ces préjugés, une théorie scientifique à large domaine de validité, une théorie du proces- sus expérimental, un appareillage construit en fonction de cette théorie locale, et enfin des éléments de « culture matérielle » (au sens de savoir- faire technique) qui permettent de mener à bien les expérimentations. Lorsqu’une résistance survient, c’est chacune des composantes du projet d’investigation qui se trouve en situation d’être interrogée, et éventuelle- ment modifiée, afin d’aboutir à l’accommodation souhaitée. Par-delà la

6The pages mentionned are the ones of the english edition. Néo-pragmatisme et incommensurabilité en physique 221 théorie scientifique générale et la théorie partielle instrumentale, qui sont souvent considérées comme les seules variables d’ajustement, la pression des résistances peut aussi conduire à modifier, en aval, la constitution et le plan de fonctionnement de l’appareillage, ou bien, en amont, les grandes valeurs portées par la société environnante. J’insisterai ici sur l’opportunité, rarement analysée, de modifier les techniques. Lorsqu’une théorie ne permet pas (ou plus) d’anticiper une certaine classe de phénomènes, il arrive que le travail d’adaptation le plus fécond ne porte pas sur elle (ou pas que sur elle), mais également sur les phénomènes qui lui sont opposés, c’est-à-dire sur leur production instrumentale. Un exemple connu est discuté par I. Lakatos [Lakatos 1978]. En 1913, une théorie quantique, celle de l’atome de Bohr, per- mettait de dériver pour la première fois avec la plus grande précision le spectre de l’atome d’hydrogène tel que l’avait établi expérimentalement Balmer quelques décennies plus tôt. Dès la fin de 1913, cependant, l’expé- rimentateur Alfred Fowler opposa à Bohr un spectre de tube à décharge qui s’écartait notablement des spécifications de la théorie à peine née. De nouvelles raies attribuées à l’hydrogène avaient des fréquences correspon- dant à des valeurs demi-entières du nombre de quantification de Bohr. Bohr soupçonna alors (et calcula) que ces nouvelles raies pouvaient cor- respondre aux transitions discrètes d’un atome d’hélium à moitié ionisé, auquel il reste un seul électron. Il suffit dans ce cas à Bohr de proposer une modification de la préparation expérimentale, consistant à rempla- cer les mélanges d’hydrogène et de traces d’hélium utilisés jusque là par des mélanges d’hélium et de traces de chlore « catalytique », pour tester l’hypothèse que les raies « demi-entières » correspondaient à l’hélium ionisé. La proposition de Bohr, couronnée de succès, consistait en une demande de « purifier » suffisamment les phénomènes par modification des conditions expérimentales pour leur faire atteindre le degré de défi- nition qu’exigeait la théorie. D’autres suggestions de correction portent non pas sur la préparation expérimentale mais directement sur l’appa- reillage de mesure. Et d’autres sources de réorientations expérimentales peuvent venir (comme chez Lavoisier) non pas tant de la théorie, que des valeurs culturelles sous-jacentes. Les résistances rétro-agissent donc parfois non pas sur le corpus de théories et présuppositions testé, mais sur les moyens performatifs et technologiques du test. Ainsi voit-on comment l’approche émergentiste et accommodative rend caduc le face-à-face rigide entre des « faits » pré-donnés et une communauté de chercheurs, qui constituait le champ clos du débat tra- ditionnel entre réalistes et constructivistes. Le jeu des pratiques est ici 222 Michel Bitbol le creuset où tous les moments de l’histoire adaptative sont susceptibles d’entrer en fusion, successivement ou simultanément. D’un côté il donne naissance à un « (. . .) processus délicat et indéfiniment ouvert de re- configuration de la culture matérielle scientifique en vue d’obtenir des manifestations matérielles qui puissent être précisément alignées avec les structures conceptuelles » [Pickering 1995, 97]. Et d’un autre côté, comme le soulignent aussi bien Laudan [Laudan 1984] que Pickering, les intérêts des acteurs sociaux de la recherche, une bonne partie des valeurs qui les orientent, et la culture intellectuelle qu’ils véhiculent, sont également remodelés après coup ou simultanément par les nécessi- tés de l’accommodation. On en vient ainsi à admettre que « (. . .) rien de substantiel [ni monde extérieur ni sujet connaissant] n’explique ou ne contrôle l’extension de la culture scientifique. La culture existante est la surface émergente de sa propre extension, dans un processus de modéli- sation indéfiniment ouvert qui n’a aucun but donné ou connaissable par avance »[Pickering 1995, 146]. L’une des clés du changement de perspective sur les sciences que propose Pickering est son remplacement des problématiques impliquant une causalité linéaire (entre la réalité et sa représentation, ou bien entre les structures cognitives et la théorie qu’elles avancent), par le concept d’un système cybernétique évolutif d’avancées et d’ajustements rétro- actifs.

5. La sous-détermination au sens pragmatique : un débat actuel

Sous ces hypothèses épistémologiques, on aboutit à une forme nouvelle de la thèse de la sous-détermination radicale des théories scientifiques (ou thèse de Duhem-Quine). Selon Hacking il s’agit même d’une ver- sion renforcée et élargie de cette thèse. Dans sa forme originale celle-ci consistait à affirmer que bon nombre de théories générales peuvent être soutenues face à un ensemble fini de « faits », pourvu que l’on modifie de façon appropriée la théorie locale du fonctionnement de l’appareillage, et que l’on remodèle ainsi la signification de ces faits. Dans la forme néo- pragmatiste de la thèse de la sous-détermination, de nombreuses théories générales peuvent être soutenues face à un ensemble fini de phénomènes, pour peu que l’on transforme adéquatement le dispositif expérimental lui- même (et pas seulement la théorie de son fonctionnement) en tant qu’il contribue à produire les phénomènes auxquels la théorie est confrontée. La plasticité du système de la recherche, sur laquelle repose la thèse de Duhem-Quine, est ici portée à un degré inégalé puisqu’elle s’étend aux Néo-pragmatisme et incommensurabilité en physique 223 conditions instrumentales mêmes qui participent à la production des phénomènes. Les « résistances » ne sont pas pour autant niées ici, pas plus que les « faits » ne l’étaient dans la version originale de la thèse de la sous-détermination. La part des facteurs modifiables lors de la négo- ciation dialectique qui aboutit à une théorie adéquate aux phénomènes a simplement été étendue aux manipulations techno-expérimentales, au lieu d’être limitée à leur interprétation théorique. On ferait, il est vrai, peu de cas de la lucidité de P. Duhem, si l’on affirmait qu’il n’a jamais envisagé la possibilité d’un ajustement de l’ins- trumentation et des projets expérimentaux dans l’activité globale du physicien. Cependant, cet ajustement ne se voit offrir par Duhem au- cun rôle explicite dans la mise en cause holistique des systèmes scienti- fiques. Seul demeure en fin de compte le face-à-face entre phénomènes et ensembles de propositions théoriques, le mode expérimental de « pro- duction » du phénomène restant à l’arrière-plan : « La seule chose que nous apprend l’expérience, c’est que, parmi toutes les propositions qui ont servi à prévoir ce phénomène et à constater qu’il ne se produisait pas, il y a au moins une erreur; mais où gît cette erreur, c’est ce qu’elle ne nous dit pas » [Duhem 1906, 281]. Toute la différence entre le « fait scientifique » et le « fait brut » se trouve ramenée par Duhem à l’en- cadrement théorique du premier, qui manque au second. Chaque enca- drement théorique fédère un grand nombre de constats de laboratoire ou « faits bruts » (actuels et potentiels) en un seul « fait scientifique » ; et à l’inverse chaque « fait brut » est susceptible de multiples interpré- tations théoriques et donc de modes variés d’articulation avec d’autres « faits bruts » en « faits scientifiques ». Mais rien ou peu de chose sur la manière dont les « faits bruts » eux-mêmes sont modelables à travers un processus complexe associant interprétation théorique, pression de valeurs cognitives parfois tacites, et modifications de choix instrumen- taux, ce qui sous-détermine encore plus le type d’ajustement adaptatif à effectuer face à une « résistance ». Les conséquences d’un élargissement des cas de sous-détermination ne sont pas négligeables pour le sort de la thèse de l’incommensurabilité. La sous-détermination des théories, si elle est radicale, ravale l’incommensu- rabilité éventuelle de deux paradigmes successifs à une simple question de commodité, de simplicité ou d’économie. Lors d’une époque de crise, il était plus commode, plus simple, plus économique, de changer radica- lement de réseau de concepts et de questions pertinentes pour rendre rai- son d’une gamme élargie de phénomènes. Mais à l’examen (et souvent de manière rétrospective), on s’aperçoit que rien n’interdisait formellement de maintenir un degré de conservatisme plus élevé que celui qui avait été 224 Michel Bitbol envisagé au départ. On aurait pu continuer à concevoir la physique mi- croscopique comme une variété (altérée par les « potentiels quantiques » de Bohm) de mécanique corpusculaire, largement commensurable sur le plan conceptuel avec la mécanique classique. On aurait pu continuer à traiter la théorie de la gravitation dans un cadre géométrique euclidien (quadri-dimensionnel, et rempli par un tenseur d’impulsion-énergie ap- proprié), au lieu de recourir à la géométrie riemanienne et au concept de géodésique, incommensurable avec celui de force. Les complexités et les composantes quelque peu « ad hoc » de ces formes théoriques alterna- tives inhibent il est vrai la tentation d’y avoir recours. Mais le seul fait de leur existence montre que l’incommensurabilité (de toutes manières partielle) n’est qu’une option parmi d’autres, dans l’éventail d’options offert par la sous-détermination des théories. L’amplification de la sous-détermination qui consiste à ajouter le choix des procédures expérimentales et la transformation des phéno- mènes « produits » par ces procédures aux paramètres d’ajustement dont disposent les chercheurs, ne fait dans ces conditions que diminuer le caractère de nécessité du changement de paradigme, et rend plus facul- tative encore la succession de paradigmes authentiquement incommen- surables. L’incommensurabilité apparaît ici plus clairement que jamais comme le fruit d’une option plus ou moins consciente, d’une bifurcation consentie dans « l’engrenage des pratiques », et elle est de ce fait toujours susceptible d’être surmontée par un retour aux conditions performatives qui lui ont donné naissance. A la réflexion, on s’aperçoit cependant que le cadre historiciste adopté par les philosophes des sciences néo-pragmatistes n’a pas seulement pour conséquence d’étendre le champ de la sous-détermination de principe des théories scientifiques ; il suggère aussi une explication plausible du fait que la sous-détermination effective de ces théories est très faible. Le nombre de degrés de liberté de la créativité conceptuelle, axiologique, et matérielle, est en effet considérablement amoindri par la condition de continuité de chaque avancée future avec la trajectoire historique qui a mené à l’état présent des sciences. On reconnaît ainsi que la contingence n’est en aucun cas synonyme d’arbitraire. Pour quelqu’un qui participe au développement cognitif, les possibilités de s’écarter de son cours sont en définitive assez restreintes, même s’il apparaît, d’un point de vue qui se voudrait extérieur à la séquence évolutive, que les choses auraient pu se passer autrement. A partir de là, un genre inédit de divergence est apparue entre les divers partisans de la conception néo-pragmatiste du développement des sciences. Contre Pickering, qui insiste sur la sous- détermination de principe, en invoquant par exemple la possibilité que Néo-pragmatisme et incommensurabilité en physique 225 la physique contemporaine n’ait pas pris la voie qui l’a conduite à postu- ler l’existence des Quarks, Hacking pense que la seule question intéres- sante à se poser est celle de la détermination de fait des théories : « La tâche philosophique est moins de comprendre une indétermination que nous sommes capables d’imaginer mais dont nous ne pouvons pas faire l’expérience, que d’expliquer la remarquable détermination des sciences de laboratoire arrivées à leur phase de maturité » [Hacking 1992].

Une question connexe est celle de savoir si, par-delà la sous-détermina- tion de principe des théories, liée à la variété des trajectoires historiques possibles du processus de la recherche, ne s’en dégagent pas quelques invariants universels. Hacking a esquissé cette interrogation [Hacking 1999], mais il l’a restreinte à une comparaison entre l’historicisme re- lativiste de Pickering et le réalisme scientifique. Après tout, remarque Hacking, un réalisme scientifique de type « convergent », entièrement tendu vers le futur, n’est pas forcément en contradiction avec la contin- gence historique de l’état présent de la science. Il n’exclut pas en effet que les voies pour parvenir au lointain objectif de la fidélité au réel soient multiples, voire pragmatiquement incommensurables du fait de leurs différentes cultures expérimentales. Dans cette perspective, l’appa- rition d’invariants qui s’imposeraient aux diverses voies d’investigation serait l’indice d’une proximité accrue (au moins dans certains secteurs) vis-à-vis de l’objectif de correspondance au réel.

Le problème est que rien n’empêche que ces invariants ne manifestent, à leur façon ambiguë, tout autre chose que des structures extérieures sur lesquelles se modèleraient les théories scientifiques. La conception histori- ciste nous incite à voir dans les théories scientifiques le produit à jamais inachevé d’une dialectique des résistances et des accommodations. Ne se pourrait-il pas que ce qui reste invariable d’une histoire dialectique à l’autre ne traduise rien d’autre que les grandes rationalités procédu- rales qui leur sont communes, en deçà de la variété des techniques et des agencements instrumentaux ? Dans ce cas, les invariants ne seraient pas moins instructifs que dans l’option réaliste. Simplement, ce sur quoi ils nous renseigneraient ne serait pas la structure de quelque réalité indé- pendante, mais les conditions de l’émergence co-dépendante dans le réel d’un système d’activités individuelles et sociales viables et d’un réseau structuré de phénomènes qui leur répondent. Il s’agit là d’une réponse historiciste au défi historiciste de la dispersion potentielle des connais- sances. 226 Michel Bitbol 6. Le cercle « vertueux » de la connaissance

Des régions de stabilité se manifestent quoi qu’il en soit dans l’histoire dialectique effective des sciences physiques, et elles demandent à être ex- pliquées. Dans la perspective néo-pragmatiste, ces régions de stabilité ne traduisent pas des « découvertes » mais des cycles-limites stationnaires d’accommodation localement optimale entre les théories et l’instrumen- tation expérimentale. Les transformations des structures théoriques et des appareillages de laboratoire se répondent, jusqu’à atteindre un état où ils deviennent, au moins pour un temps, « (. . .) mutuellement auto- justificateurs »[Hacking 1992]. La forme la plus élémentaire de l’auto- justification mutuelle est, selon Hacking, celle du « cercle vertueux » dans lequel « (. . .) nous créons l’appareillage qui engendre des données qui confirment des théories ; nous jugeons l’appareil par son aptitude à produire des données qui collent [à la théorie] » [Hacking 1992]. Une phrase comme celle-ci, peut il est vrai faire penser à un cercle vi- cieux autistique plutôt qu’au cercle vertueux invoqué par Hacking. L’im- pression se dissipe cependant à condition que l’on introduise les nuances indispensables sur la portée limitée qu’a ce genre d’auto-confirmation. Les verbes « engendrer » ou « produire » sont à interpréter, nous l’avons vu, dans le sens de « co-engendrer » ou « co-produire » : la part spécifiée, contrôlée, de la préparation expérimentale collabore avec sa part non- spécifiée, non-contrôlée, dans l’émergence du phénomène. Par ailleurs une appréciation préalable de la qualité de l’appareillage fondée sur la ca- pacité qu’a celui-ci à (re)produire des phénomènes que prévoit la théorie en vigueur, n’est légitime que dans une phase d’étalonnage préparatoire. Indubitablement, l’étalonnage des appareils exige que l’on sache d’avance à quoi s’attendre en ce qui concerne une certaine classe, restreinte et bien maîtrisée dans le passé, de phénomènes. Mais une telle exigence n’exclut en rien l’apparition de résistances en cas de sortie impromptue hors du domaine de validité de la théorie lors d’une phase expérimentale posté- rieure à l’étalonnage. La recherche s’étend inévitablement au-delà de la base de phénomènes qui sert à la mise au point de l’appareillage. Une fois ces précisions apportées, le cercle de Hacking s’avère effectivement « vertueux ». La raison pour laquelle on peut le qualifier de vertueux est qu’il est pleinement ouvert. Il est non seulement ouvert à l’inattendu en provenance de la part non-spécifiée du dispositif expérimental, mais aussi ouvert à une redéfinition de la base d’étalonnage une fois que de nouveaux champs théoriques ont été suffisamment assurés pour jouer le rôle de « certitudes » indiscutées. Néo-pragmatisme et incommensurabilité en physique 227

Le concept de cycle-limite présente l’avantage de dépasser l’opposition habituelle et sans issue entre la thèse de la vérité-correspondance et une thèse faisant reposer la vérité des théories sur leur seule cohérence in- terne. Au lieu de cela, on se trouve conduit à adopter une thèse faisant intervenir tout à la fois « (. . .) la cohérence de la pensée, de l’action, du matériel, et des marques écrites [sur les sorties graphiques ou numériques des appareils de mesure] »[Hacking 1992]. En d’autres termes, la solu- tion proposée consiste en une extension de la thèse de la vérité-cohérence, initialement confinée dans l’univers intellectuel, aux pratiques, aux ap- pareillages, et aux phénomènes qui s’y manifestent. Il y a bien sûr un élément à première vue surprenant, pour ne pas dire choquant, dans cette idée de cohérence étendue aux pratiques. Comme me l’a signalé à juste titre Léna Soler, la cohérence est une clause qui s’applique en toute rigueur aux idées plutôt qu’aux choses, aux énoncés, y compris ceux qui portent sur des dispositifs expérimentaux, plutôt qu’aux simples gestes et matériaux du laboratoire. La première réponse qu’on peut faire à cette objection est conforme à ce qui a été proposé dans le premier paragraphe du présent article. La cohérence élargie de Hacking peut être conçue dans une certaine mesure comme portant sur des énoncés, pourvu qu’on admette que cer- tains de ces énoncés font partie de l’arrière-plan de présupposés auquel s’adossent les pratiques, et sont donc seulement tacites ou virtuels. La seconde réponse est qu’il n’est pas inconcevable de donner plus direc- tement sens à l’idée de cohérence (ou plus directement d’absence de cohérence) entre énoncés et pratiques, en ayant recours au concept de « contradiction performative » dû à K.-O. Apel. Il est performativement contradictoire d’argumenter contre la validité de toute argumentation, car l’acte d’énonciation s’inscrit en faux contre le contenu de l’énoncé. Il est performativement contradictoire d’utiliser un dispositif interféromé- trique pour produire des phénomènes optiques nouveaux (comme l’holo- graphie) si l’on adhère à la théorie corpusculaire de la lumière de Newton, car la configuration de l’appareil ne correspond à aucun effet prévisible au moyen de cette théorie. Ici, des « faire » s’opposent à des « dire », et il semble possible d’en inférer a contrario que seuls certains « faire » s’ac- cordent avec d’autres « dire ». Ce genre d’accord est ce qu’on appellera la cohérence généralisée. La thèse de la vérité-cohérence généralisée a d’autres conséquences. Dans le cadre de cette thèse, tout ce que l’on peut dire d’une théorie est qu’elle est vraie de cette catégorie (éventuellement très large) de phé- nomènes, qui se manifeste au moyen de cette classe idéalisée d’activités coordonnées et de cette sorte de matériel instrumental. Inversement, 228 Michel Bitbol lorsqu’une nouvelle résistance apparaît, déstabilisant un cycle-limite, celle-ci n’a pas à être conçue comme un élément d’information rendant la théorie associée « fausse » au sens d’une non-correspondance à la source réelle extérieure des informations. Elle signale simplement que le cercle actuel des pratiques, des organisations matérielles, et des concepts, est sorti par inadvertance du champ d’opérativité non-artificielle des règles théoriques et performatives qui régissaient le cycle-limite précédent ; et elle donne de ce fait le coup d’envoi à une nouvelle dialectique évolutive des résistances et des accommodations. La stabilisation d’un nouveau cycle peut se faire selon plusieurs modalités (selon le degré de généra- lité de ce cycle). Il peut au maximum inclure le cycle-limite précédent comme un cas particulier valant pour une classe restreinte de pratiques. Il peut aussi conduire à définir une nouvelle discipline et un nouveau domaine d’études disjoint du premier, ou au contraire amener à uni- fier des champs disciplinaires initialement pensés comme distincts. Dans tous les cas, le caractère de discontinuité-incommensurabilité des para- digmes successifs ou coexistants se trouve pris en charge par l’idée de cycles-limites disjoints. L’usage qui est fait de l’idée d’un cycle de constance théorético- performative obtenu à l’issue d’un itinéraire de recherche, varie cepen- dant d’un auteur à l’autre. Sa composante relativiste, contenue dans le concept d’une vérité pour tel cycle de pratiques, est le foyer du débat. Hacking attache une importance décisive au détachement progressif du « cercle vertueux » des résistances et des accommodations à l’égard des circonstances socio-historiques qui l’ont accompagné pendant sa phase de stabilisation. De là vient sans doute l’affinité de sa position avec le réalisme des entités : si un cycle théorético-performatif stable, unique, et complètement autonome vis-à-vis de l’histoire de sa production, s’est mis en place, alors aucun obstacle ne s’oppose à ce que l’on traite comme réelles celles des entités que la théorie générale désigne comme étant manipulables (fût-ce médiatement). Par contraste, Pickering et Gooding apparaissent beaucoup moins disposés à laisser leur « réalisme pragma- tique » dévier, de concession en concession, vers des thèses standard du réalisme scientifique. Pickering admet certes la possibilité qu’advienne un « gel » des procédures, une itération « machinique » des gestes, une stabilisation interactive de la « danse » des pratiques et des orientations théoriques en une « chorégraphie » réglée une fois pour toutes [Picke- ring 1995, 102]. Mais il ne cesse d’insister sur le caractère émergent (et donc sur les antécédents dynamiques et historiques) de ces « clôtures » cycliques. Et il souligne (ce qui le range dans le camp d’un relativisme historiciste) que, selon lui, la trace de l’histoire qui a conduit à chaque Néo-pragmatisme et incommensurabilité en physique 229 cycle ne peut pas en être effacée. De même, selon Gooding, il ne faut pas perdre de vue les « (. . .) relations entre les aptitudes technologiques des observateurs et leur confiance dans la validité de leurs représentations. Certaines de ces représentations deviennent si stables qu’elles cessent d’être conçues comme des synthèses qui ont émergé d’un processus de convergence entre le possible et l’actuel. Au lieu de cela, elles sont consi- dérées comme correspondant à des choses (également stables) dans le monde »[Gooding 1992]. En d’autres termes, la stabilité immanente des cycles de pratiques et d’anticipations théoriques est projetée en stabilité transcendante des entités de la théorie ; et, réciproquement, le postu- lat de la transcendance de ces entités favorise la reproduction du cercle théorético-performatif qui l’autorise. Une objection sérieuse que je ferai aux principaux protagonistes de ce débat est que la situation inaugurée par la physique quantique ne s’accorde facilement avec aucun des deux principaux schémas qu’ils pro- posent. D’un côté, la mécanique quantique apparaît, dans son formalisme standard, largement dégagée des contingences historiques, culturelles, et conceptuelles, qui y ont conduit. La raison en a déjà été exposée en introduction : ce formalisme a été conçu par Dirac et Von Neumann à partir de deux théories initiales (la mécanique matricielle et la mécanique ondulatoire) qui dérivaient de deux séries de modèles antinomiques, res- pectivement discontinuiste et continuiste. En tant que résidu abstrait, ou plus petit dénominateur commun, de ces deux lignées antagonistes, le formalisme quantique était condamné à retenir le moins possible de l’une comme de l’autre. Mais d’un autre côté, cette forte déshistoricisation de la théorie quan- tique est loin d’avoir levé toutes les difficultés à une conception pleine- ment réaliste de ses entités. Des obstacles considérables se dressent face à ceux qui soutiennent de telles conceptions. Il est en particulier exclu de passer du concept d’« observable » ‘a celui de propriété (qui justifierait l’attribution d’un prédicat à quelque chose), ou encore du concept de nombre de quanta d’excitation d’un oscillateur du « vide quantique » à celui d’objets spatio-temporellement localisés individuels et réidentifiables (qui justifierait de faire référence à un quelque chose d’isomorphe au corps matériel). De nombreuses difficultés rendent peu plausible (ou fragmentaire) la projection sous forme d’entités transcendantes de la stabilité immanente des grands cycles théorético- performatifs associés à la mécanique quantique. Ici, par conséquent, on a le sentiment que l’alternative habituelle, entre le maintien du lien des théories avec l’histoire de leur émergence, et un réalisme fondé sur 230 Michel Bitbol l’anhistoricité de ces mêmes théories, ne fonctionne plus. S’il en est ainsi, c’est que le formalisme de la mécanique quantique traduit non pas la dialectique effective de résistances et d’accommodations dont elle est le fruit, mais une vaste classe, jusqu’à présent exhaustive, de résistances et d’accommodations possibles. Au lieu de se contenter de recueillir ré- trospectivement le produit des cycles d’ajustement, la mécanique quan- tique a formalisé prospectivement les conditions de tout processus de recherche associant la « production » de phénomènes non-séparables de leur contexte et le projet d’en unifier l’algorithme prédictif. En somme, aussi déshistoricisée que soit la mécanique quantique, elle porte dans la structure même de son formalisme la trace d’une impossi- bilité à détacher les phénomènes dont elle rend compte des circonstances expérimentales de leur manifestation. La stabilité immanente des cycles de pratiques et d’anticipations théoriques ne peut pas ici (sauf artifice) être interprétée comme signe de la stabilité transcendante d’entités quel- conques. Le fait que des manipulations couronnées de succès s’effectuent sous le présupposé de l’existence de telles entités n’atténue en rien ce constat. Car ce présupposé, qu’on n’est en droit de maintenir que lo- calement, entre les limites requises par l’activité guidée par lui, n’a pas l’universalité requise pour être projetée ontologiquement. Une réflexion sur la mécanique quantique s’inscrit au total en faux à la fois contre l’historicisme relativiste et le réalisme des entités. Elle invite selon moi, et selon plusieurs autres auteurs, à une approche néo-transcendantaliste des théories physiques, incluant des composantes pragmatistes mais ne s’y réduisant pas.

7. Sur les mathématiques et l’expérimentation

La question lancinante de la « déraisonnable efficacité des mathéma- tiques dans les sciences de la nature »[Wigner 1979] est également abor- dée par le courant de philosophes des sciences néo-pragmatistes. Picker- ing établit une distinction entre au moins trois niveaux de la dialectique de résistances et d’accommodation, parmi ceux qui sont les plus centraux pour la pratique scientifique. Trois niveaux que leur aptitude à rétro-agir l’un sur l’autre ne doit pas conduire à confondre. L’un de ces niveaux concerne les pratiques de laboratoire, le second concerne les théories mathématiques, et le troisième, qui implique la recherche de l’« aligne- ment » des deux premiers, concerne les théories physiques. La remarque centrale est ici que les théories mathématiques proprement dites émer- gent, comme les théories physiques, d’une dialectique de résistances et d’accommodations ; à ceci près que dans leur cas les résistances ne provi- Néo-pragmatisme et incommensurabilité en physique 231 ennent pas d’une « générativité matérielle » à l’œuvre dans la chaîne des instruments expérimentaux, mais d’une « générativité disciplinaire »7 imposée par des règles de manipulation symbolique universellement ac- ceptées. Par la suite, le processus créatif des mathématiques est à son tour décomposé en trois étapes : une étape d’extension hypothétique des mo- dèles antérieurs, une étape de « transcription » déductive encadrée par la discipline des règles admises, et une étape finale de « remplissage » (par des règles inédites) des relations symboliques que les règles précédentes laissaient indéterminées. Celle des trois étapes qui rend très tentante l’in- terprétation réaliste des entités mathématiques, parce qu’elle confère à leur système une forme d’autonomie et d’imprévisibilité, est la transcrip- tion déductive. Alors que les deux autres étapes, l’extension hypothétique et le remplissage, sont essentiellement libres (même si elles peuvent être inspirées par la culture ambiante), la transcription déductive est rigou- reusement contraignante. Elle suscite de ce fait le sentiment qu’il est impossible d’en maîtriser le cours. Ici comme ailleurs, la combinaison d’une visée directionnelle (par prolongement idéal), et d’un système de contraintes à la productivité insondable, trouve une expression commode dans la croyance (platonicienne) en des entités transcendantes. La question qui doit à présent être posée de façon plus précise, dans un cadre néo-pragmatiste, est celle du rapport entre mathématiques et sciences physiques. Un point commun crucial entre les pratiques mathé- matiques et les pratiques expérimentales de la physique est leur confron- tation à des résistances; des résistances qui se présentent comme des réactivités dont la forme dépend de l’organisation d’une activité de re- cherche. Dans un cas, des résistances systématiques sont imposées à un projet créatif par une discipline déductive. Dans l’autre cas, des résis- tances occasionnelles se manifestent à l’intérieur d’une instrumentation préalablement agencée en fonction d’un programme de recherche. Dans le premier cas les résistances prennent corps au cours d’une succession d’opérations strictement intra-symboliques. Dans le second cas, il est vrai que les résistances « matérielles » qui surviennent sont également traductibles sur le plan symbolique par des propositions (elles acquièrent alors le statut de « faits »). Mais la caractéristique distinctive des résis- tances dont doivent tenir compte les sciences de la nature, par rapport à celles des mathématiques, est leur capacité à se traduire par des obstacles

7Ces expressions « générativité matérielle » et « générativité disciplinaire » tendent à traduire, de façon inévitablement imparfaite, mais suffisamment évoca- trice dans ce contexte, les expressions anglaises « material agency » et « disciplinary agency »[Pickering 1995, 116]. 232 Michel Bitbol concrets au déploiement d’une activité elle-même concrète de maîtrise de l’environnement. L’« alignement » dont parle Pickering peut dans ce cas être conçu comme une procédure de sélection de celles des structures symboliques et résistances disciplinaires qui sont aptes à envelopper par le jeu de leurs possibilités les structures opératoires et les résistances actuelles d’une certaine catégorie d’activités concrètes de recherche. En s’affranchissant de la conception « platonicienne » des mathématiques, on évite du même coup d’avoir à affronter le mystère d’une correspondance entre les entités du ciel des idées mathématiques et les entités transcendantes du monde physique. Il faut souligner une nouvelle fois ici le rôle particulier que joue (fût- ce à demi-mot) la physique quantique dans le processus qui conduit à asseoir la crédibilité de ce genre de conception. Sur fond d’une discussion de la seule physique classique, on aurait en effet pu objecter qu’interpré- ter les entités mathématiques comme projections d’un cycle réversible d’opérations symboliques, et les entités naturelles comme projections stables d’un cycle-limite de pratiques expérimentales et d’anticipations corroborées, ne fait qu’introduire des complications inutiles. Puisque les épistémologues néo-pragmatistes eux-mêmes conviennent de la récipro- cité de la relation (à la fois projective et régulatrice) entre cycles de pratiques et entités postulées, y a-t-il une raison de ne pas adhérer sans réserve à la manière dont les physiciens eux-mêmes en viennent à élimi- ner de leur discours l’échafaudage des pratiques pour traiter des seules entités ? Et y a-t-il davantage de raisons (si ce n’est peut-être de principe) de ne pas prendre au sérieux leur méta-représentation d’une correspon- dance entre des entités naturelles et les entités théoriques qui visent à les représenter ? Bien des choses changent en revanche si l’on a à tenir compte d’une théorie comme la mécanique quantique standard ; c’est-à-dire d’une théo- rie dont les symboles ne sont pas immédiatement interprétables comme représentant des déterminations appartenant en propre à une collection d’entités naturelles, mais comme instruments de prédiction probabiliste de phénomènes obtenus sous des conditions expérimentales spécifiées. Car dans ce cas l’idée de conférer à la théorie le statut purement « gram- matical » d’un ensemble de normes d’orientation prédictive n’a plus a être justifiée par un travail archéologique portant sur les circonstances de sa formation et de son utilisation effective ; elle s’impose d’emblée, en première instance. Au contraire, c’est la tendance habituelle à tenir une théorie pour la représentation d’un système de relations entre les entités naturelles qui requiert désormais une justification longue, diffi- Néo-pragmatisme et incommensurabilité en physique 233 cile, et semée d’embûches ; une justification qui en appelle tantôt à des logiques non-classiques tantôt à des influences instantanées à distance entre processus principiellement inaccessibles à l’expérience.

8. Conclusion

En fin de parcours, nous avons peut-être réussi à compenser (ou à in- verser) un curieux déséquilibre du débat épistémologique que B. Van Fraassen a décrit en ces termes : « (...) le réalisme gagne par défaut. Et cela a été la stratégie du réalisme tout au long des âges, gagner par défaut une fois qu’il a explicité ce que son adversaire doit faire pour gagner »[Van Fraassen 1975]. Longtemps, en effet, les épistémo- logues réalistes ont pu se soustraire aux critiques souvent pertinentes de leurs adversaires anti-réalistes en s’abritant derrière l’incapacité de ces derniers à rendre compte des deux traits distinctifs du travail scienti- fique : l’efficacité d’une activité guidée par la visée régulatrice d’entités et de lois, et l’orientation de ces visées en fonction de contraintes dont le chercheur n’est pas maître [Bitbol 1998]. L’idée d’une réalité exté- rieure pré-structurée qui serait à la fois l’objet de la visée et la cause des contraintes, semblait être la seule réponse disponible au double défi for- mulé par les réalistes scientifiques. Mais à partir du moment où des alter- natives épistémologiques comme l’empirisme constructif de Van Fraassen ou le néo-pragmatisme de Pickering et Hacking, sont parvenues à four- nir un compte-rendu fonctionnel des visées régulatrices des sciences, et à montrer comment les « résistances » (plutôt que les contraintes) peuvent dépendre de l’activité guidée par ces visées régulatrices, l’idée d’une coïn- cidence entre objet des visées et source exclusive des contraintes n’a plus rien d’impératif. Désormais, la charge de la preuve a été transférée au réa- lisme scientifique, et les discussions de philosophie des sciences comme celle sur l’incommensurabilité ont de bonnes raisons d’être conduites, fût-ce par défaut, dans le cadre tracé par les néo-pragmatistes. Dans ce cadre, on l’a vu, comparer deux paradigmes ne suppose pas seulement de mettre en regard deux représentations du monde et deux langages associés, mais aussi et surtout deux manières d’intervenir dans le monde. L’intérêt principal de ce sens élargi du concept de paradigme est qu’il requiert plus manifestement encore que le premier quelque chose d’autre qu’une simple traduction. Soit une véritable simulation (virtuelle ou actuelle) de ce que c’est d’être (le « What it is like to be » de Th. Nagel) dans l’autre système de pensée et d’action, ce qui laisse subsister une forme d’incommensurabilité. Soit l’adoption d’une manière d’être et 234 de chercher qui englobe les précédentes ou en fait un libre usage alterné, ce qui permet de dépasser l’incommensurabilité par la mise en place d’une sorte de méta-niveau performatif. Le déplacement systématique des interrogations à un méta-niveau par rapport aux niveaux historiques antérieurs se trouve à vrai dire accompli presque automatiquement au cours de l’avancée des sciences. Avec l’argument de la sous-détermination généralisée, cela suffit à faire perdre à l’« incommensurabilité » alléguée une bonne partie de sa rigidité. Un intérêt dérivé de ce sens élargi du concept de paradigme est qu’il rejoint une évolution récente des sciences de l’esprit et de la cognition, sur laquelle semblent curieusement s’accorder les « mystérianistes », les dualistes, et les éliminativistes neuro-physiologiques. Prenons l’exemple de la thèse éliminativiste. Les époux Churchland (défenseurs embléma- tiques de l’éliminativisme) ont réagi avec une certaine audace épistémo- logique aux psychologues qui leur reprochent : (a) d’ignorer que la « folk- psychology » est plutôt un art de « se mettre à la place » d’autrui qu’une authentique théorie de l’esprit, et (b) de chercher par conséquent à tort à éliminer la « folk-psychology » comme on le ferait d’une théorie scien- tifique périmée. Selon les Churchland, l’erreur que font leurs adversaires est de considérer une théorie scientifique comme un pur symbolisme re- présentatif. Ils considèrent pour leur part, en accord ouvert avec Kuhn, qu’apprendre une théorie « (. . .) n’est pas seulement ou même priori- tairement une question d’apprentissage de lois et de principes : c’est une question d’apprentissage d’une pratique sociale complexe » [Chur- chland & Churchland 1998, 11, 33]. Par conséquent, concluent-ils, la folk-psychology, dont l’assimilation suppose l’intégration d’une pratique sociale, n’a pas de raison de ne pas être considérée comme une théorie. Et, en tant que théorie, rien n’empêche de la mettre à l’écart comme toute autre théorie dépassée. Je ne me préoccuperai pas ici de savoir si cette redéfinition kuhnienne des théories suffit à répondre à l’objec- tion des défenseurs de la « folk-psychology », ou si elle ne revient pas au contraire à leur faire une concession décisive [Bitbol 2002]. Mais ce qui me frappe est de constater que la discussion sur les théories, les paradigmes, et leur incommensurabilité alléguée, tend effectivement à se déplacer partout sur un plan pragmatique. Non seulement dans la théorie philosophique de la connaissance, mais aussi, on le voit avec les Churchland, dans les projets de théorie naturalisée de la cognition. Incommensurability and laboratory science∗

Emiliano Trizio Universities of Paris-X Nanterre et Venezia Ca’ Foscari

Résumé : Le but de l’article est d’établir des relations entre, d’une part, la caractérisation générale kuhnienne de l’incommensurabilité comme impossibi- lité de traduire l’une dans l’autre les taxinomies de théories scientifiques rivales et, d’autre part, la version plus spécifique de l’incommensurabilité proposée par Hacking, laquelle porte sur des théories concurrentes s’étant stabilisées en re- lation à des équipements de laboratoire et des techniques de mesure différents. Sur la base d’une analyse, inspirée des travaux de Duhem, de la nature des taxinomies scientifiques, on soutiendra que l’approche linguistique kuhnienne est inadéquate pour rendre compte de la manière dont les termes scientifiques s’appliquent à la nature dans le domaine des sciences de laboratoire, au sein desquelles le rôle des opérations de mesure est essentiel. L’analyse introduira la notion de taxinomie duale et celle de caractère ostensif d’une théorie. Il apparaîtra que, une fois ces deux notions prises en compte, il devient possible de poser les bases d’une version taxinomique élargie de l’incommensurabilité, susceptible de fournir un cadre commun pour la discussion des exemples in- troduits par Kuhn et Hacking. Abstract: The aim of the article is to establish relations between Kuhn’s general characterization of incommensurability as the impossibility to trans- late the taxonomies pertaining to rival scientific theories into one another

∗I wish to express my deep gratitude to Léna Soler, whose many comments and suggestions have compelled me to rethink various aspects of this article and to modify it in a substantial way. It is also a pleasure to thank Matteo Bevilacqua, Emiliano Boccardi, Fantina Madricardo, Ayesha Mian, Anna Sartori and the anonymous ref- erees of Philosophia Scientiæ for helping me to improve its form and content.

Philosophia Scientiæ, 8 (1), 2004, 235–266. 236 Emiliano Trizio and Hacking’s more specific version of incommensurability affecting compet- ing theories that have stabilized relatively to different laboratory equipments and measurement techniques. On the basis of an analysis of the nature of sci- entific taxonomies that takes its inspiration from the works of Duhem, it will be argued that Kuhn’s language-based approach is inadequate to provide an account of the way scientific terms apply to nature in the domain of physical laboratory science, in which the role of measurement procedures is essential. The analysis will be carried out by introducing the notion of dual taxonomy and the notion of ostensive character of a theory. It will result that, once these two notions are taken into account, it becomes possible to lay the foundations of an enlarged taxonomic version of incommensurability which can provide a common framework for the discussion of the examples introduced by Kuhn and Hacking.

1. Introduction: Kuhn’s linguistic version and Hack- ing’s “literal” version of incommensurability

It is well known that Kuhn has increasingly stressed over the years the role of language, meaning and translation in his account of revolutionary changes and incommensurability1. He has also explained that this evolu- tion was coherent with the problems that originally motivated the intro- duction of this notion: namely those faced by the historian when trying to interpret old scientific texts, which, to a modern reader, seem often more obscure and nonsensical than simply wrong or outdated. Kuhn came to believe that this interpretative work requires, in a non-trivial sense, the understanding of the language in which those texts were writ- ten [Kuhn 1983a, 56-57]2 for, “the appearance of nonsense could be re- moved by recovering older meanings for some of the terms involved, meanings different from those subsequently current” [Kuhn 1990c, 91]. Following this line of reasoning, he compared the task of the historian with that of the linguist and became deeply interested in the works of Quine on meaning and translation [Kuhn 1970b, 165]. It must be stressed that although (contrary to Hacking3) Kuhn deems the theory of meaning necessary to any satisfactory account of scientific knowledge [Kuhn 1993, 229], he restricts its role in the discussion of in- commensurability to the treatment of “taxonomic terms” or “kind terms”

1On the evolution of the concept of incommensurability in Kuhn’s writings after its introduction in 1962 see [Hoyningen-Huene 1989, 206-222] (the pages mentionned are the ones of the english edition). 2For all the papers contained in [Kuhn 2000], the pages mentionned are the ones of this last book. 3See, for instance, [Hacking 1983, 43-45]. Incommensurability and laboratory science 237

[Kuhn 1990c, 92]. Different theories have a different lexical taxonomy, (which Kuhn calls also lexicon [Kuhn 1990c, 93]). When translation be- tween such lexical taxonomies is (at least partially) impossible, the two theories are said to be incommensurable: there is no common measure in the sense that “there is no language, neutral or otherwise, into which both theories, conceived as sets of sentences, can be translated without residue or loss” [Kuhn 1983a, 36]. Kuhn’s linguistic-taxonomic account of incommensurability is far from being the only one. Since its introduction in 1962, the concept of incom- mensurability has given rise to several attempts to grasp the main idea underlying the purported “lack of common measure” that the word by itself suggests. Kuhn’s departure from a literal interpretation of the concept, as we have seen, comes along with his stress on language and translatability (incommensurability = no common language). Hacking and Pickering have instead maintained that incommensurability can also be interpreted in a non-metaphorical way, when the essential role played by measurement instruments and procedures in laboratory science are taken into consideration. While Kuhn, as it will repeatedly be stressed, develops a highly general account of incommensurability, which applies to common sense language as well as to scientific theories of any degree of complexity, Hacking and Pickering have devoted special attention to the relation between rival theories whose development is deeply intertwined with the stabilization of different and incompatible laboratory practices and equipments. According to Hacking, “Stable laboratory science arises when theo- ries and laboratory equipment evolve in such a way that they match each other and are mutually self-vindicating” [Hacking 1992, 56]. As self-vindication does not exclude the possibility that more refined instru- ments produce new sets of data incompatible with the available theories, laboratory sciences can undergo deep crises that call for the development of new theories. This development takes place as a complex, mutual maturation of theory and experiment leading to a new stabilized stage of laboratory science. Yet the old theory is still compatible with the old sets of instruments and data. This fact is essential to Hacking’s views on incommensurability.

Kuhn (1961) noticed almost all of this with characteristic precision. Fetishis- tic measurement sometimes hints at anomaly that can only be tackled by devising new categories of instruments that generate new data that can be interpreted only by new sort of theory: not puzzle solving but revolution. This is the overriding theme of his study of black-body radiation (Kuhn 1978). He omitted only the fact that the old theory and its instruments 238 Emiliano Trizio

remain pretty much in place, in their data domain. Hence new and old the- ory are incommensurable in an entirely straightforward sense. They have no common measure because the instruments providing the measurements for the one are inapt for the other. This is a scientific fact that has nothing to do with “meaning change” and other semantic notions that have been associated with incommensurability. [Hacking 1983, 43-45]4 .

Hacking distinguishes this kind of incommensurability from the one that concerns the translation between kind terms that he discusses in another article [Hacking 1993, 275-310]. His two separate treatments have a lot in common, for they are both based on Hacking’s fundamental unwill- ingness to interpret science (and knowledge in general) solely in terms of notions such as language and meaning at the expenses of its practical and material dimension. Although I would not subscribe to the view that a theory of mean- ing is altogether unnecessary in the philosophy of science, the general point of view that I will adopt in this article is close to that of Hack- ing. The fact that theories can be considered up to a certain extent as sets of sentences or, at any rate, as abstract meaning structures, has led many philosophers (in primis the logical empiricists) to neglect the crucial role played by practice and manipulation in science. Science was thus reduced to the pair language/observation and little effort was made to analyse in detail what the notion “observation” really amounts to in science and what goes with it. As it is well known, Kuhn, along with others, has contributed to the overthrow of logical empiricism, precisely by blurring the distinction theory/observation; but, I will argue, he has done it in such a way that language has been granted a role, which is, if possible, even more prominent than it used to be. Kuhn’s analyses do not focus on the different status of the operations that allow differ- ent types of scientific theories and taxonomies to apply to the world. His study of exemplars, which I will discuss later in some detail, under- writes this interpretation. I will try to give an account of “how scientific terms attach to nature” that takes into consideration these differences, with special attention to the distinction between observation and mea- surement. The aim of this analysis will be to show that the two kinds of incommensurability just referred to can be accommodated in an en- larged taxonomic version, which takes into account the distinctive roles of observation, experimental practices and measurement procedures. One terminological clarification concerning the meaning of the term “taxonomy” is indeed necessary. In Kuhn’s works terms like “vocabulary”,

4See also [Pickering 1984, 407-414], and [Pickering 1995, 186-192]. Incommensurability and laboratory science 239

“structured vocabulary” [Kuhn 1989, 61], “conceptual vocabulary” [Kuhn 1991, 220], “lexicon”, “lexical taxonomy”, “cluster of terms” [Kuhn 1989, 65] are employed more or less as synonyms. One has the impression that he tends to prefer “taxonomy” or “lexical taxonomy” when he refers to theories (like ancient astronomy) whose concepts can be ordered in “trees” on the basis of the relation between genera et species [Kuhn 1991, 218], while he is more inclined to speak simply of “lexicon” or “cluster of terms” when he discusses the conceptual structures of physico- mathematical theories such as Newtonian mechanics [Kuhn 1989, 65-66]. Yet it seems to me that he intends to analyse a theory’s conceptual vocabulary without presupposing that its structure is that of a classical “aristotelian” taxonomy. Hacking, on the contrary, discusses kuhnian incommensurability on the basis of a precise definition of “conceptual taxonomy” in terms of the relation genus/species and of the existence of a summum genus or category at the top of the tree [Hacking 1993, 286], [Hacking 2003]. In what follows, I will use the word “taxonomy” in what I take to be Kuhn’s loose sense, without assuming that the conditions defining tree-like taxonomies are always fulfilled and I will employ the aforemen- tioned companion expressions more or less according to the kuhnian usage. This choice is justified by the fact that many of Kuhn’s analyses concern conceptual clusters whose structure cannot be reduced to that of a taxonomic tree5. In general, we can say that the problem of char- acterizing the nature of revolutionary scientific development demands that an account of scientific conceptualization be given, and the tree-like taxonomic pattern based on the genus/species relation does not seem to be apt to accommodate the huge variety of conceptual structures that we encounter in science. This becomes more apparent when physico- mathematical theories6 are taken into account7. The plan of the article is the following:

• in section 2 a comparison developed by Nancy Cartwright between Kuhn’s and Duhem’s accounts of the relation between theory and observation will be discussed. It will result that a discussion of the

5Sometimes what Kuhn calls a “lexicon” even includes laws of nature and conse- quently cannot be thought of as a mere structured set of kind terms, “Once mass and the second law have been added to the Newtonian lexicon in this way, the law of gravity can be introduced as an empirical regularity” [Kuhn 1989, 70] (emphasis added). I will avoid this admittedly deviant usage. 6Throughout the article I will refer to physico-mathematical theories, terms or taxonomies as those specifically pertaining to modern mathematized physics. 7As it was shown already by [Cassirer 1910], especially chapters I and IV. 240 Emiliano Trizio

way scientific terms attach to nature requires, in the case of math- ematical physics, a careful analysis of laboratory practices. Such an analysis appears to be missing in Kuhn’s writings, which focus mainly on the use of scientific language in teaching, learning and theorizing, without an acknowledgement of the ultimately essential role of experiments. • In section 3 some of Duhem’s penetrating insights on the subject are recalled and, • in section 4, they are taken as the starting point for a characteri- zation of the nature of conceptualization in laboratory science. It is claimed that what Duhem’s analysis shows is that physical ide- alizations differ from everyday observational concepts not so much because they are more general and abstract, but because, in or- der to apply them to the world, one must simultaneously yield a theoretical interpretation of whatever contributes to define the experimental context that renders their application possible. Tax- onomies belonging to mathematical physics will thus be described as dual, in the sense that they subsume natural entities and pro- cesses only if they co-subsume practical contexts and laboratory items. • These results will be used in section 5 to criticize Kuhn’s language- centred account of the way scientific terms attach to nature. It will be argued that his language-relative developmental character- ization of the theory/observation distinction is unable to capture the essential difference existing between taxonomies that can be applied perceptually and taxonomies that require acts of measure- ments (and that are therefore dual). • In section 6 Kuhn’s failure to recognize the importance and speci- ficity of laboratory practices will be shown to be a consequence of the fact that his analysis conflates learning and understanding scientific terms with their authentic application to nature. • The notion of dual taxonomy will be further clarified and illus- trated with the aid of an example in section 7. • In section 8 the application of scientific theories outside the lab- oratory will be briefly discussed. For this purpose the notion of ostensive character of a theory will be introduced. Theories can be classified according to the degree of perceptual accessibility of the objects and processes they are about (the ostensive character). Incommensurability and laboratory science 241

Much of contemporary laboratory science corresponds to a stage at which theories have very weak or no ostensive character at all and whose taxonomies can be applied to the world only via the mediation of measurement instruments.

• Finally, in section 9, on the grounds of the preceding analyses, the main ideas for an enlarged taxonomic version of incommensurabil- ity will be introduced.

2. Cartwright on Duhem and Kuhn

Nancy Cartwright has drawn attention on some essential features com- mon to Duhem’s and Kuhn’s accounts of the relation between theory and observation. Her starting point is that observation is theory-laden and that Kuhn has helped us to see it. Nevertheless, she goes on, “(. . . ) to admit that observation is theory-laden is a long way from denying that there is a theory/observation distinction”. She rightly points out that terms used by scientists can be and often are more recondite than those used in every-day life. Disagreement begins as soon as one wonders how the dividing line has to be drawn. Cartwright quotes a long passage taken from section 3 of the Postscript of The Structure of Scientific Rev- olutions to the effect that Kuhn too sees a gap between the abstract and symbolic generalizations of physical theory and the concrete situations to which they apply. I will start my analysis from that passage just as Cartwright does. The central notion of the passage is that of paradigm as shared ex- ample8. To illustrate it Kuhn considers Newton’s second principle (or law) of dynamics f = ma. According to him the meaning and cognitive content of the principle is not located at a purely theoretical level. The kuhnian classical move to understand the real cognitive content (and, as we shall see, not an innocent one) is to resort to an analysis of the way the members of the community have learned to apply the expression to some paradigmatic concrete situations. According to Kuhn f = ma is, rather than a simple law, a law-sketch or a law-schema. Students learn how to use different versions of it by being exposed to paradigmatic cases of classical dynamical systems such as a free falling body, a simple pen- dulum, a pair of harmonic oscillators, etc. In each case they are taught

8It is worth recalling that this notion constitutes the fourth components of the disciplinary matrix, which in turn represents what the members of a scientific com- munity share during a period of normal science (see [Kuhn 1970a, 181-187]). 242 Emiliano Trizio how to recognize masses, forces and accelerations and how to pick up the suitable variants of Newton’s law. Kuhn concludes:

The resultant ability to see a variety of situations as like each other, as subject for f = ma or some other symbolic generalisation, is, I think, the main thing a student acquires by doing exemplary problems, whether with pencil and paper or in a well-designed laboratory 9.

That is, Kuhn can say, “At the start and for some time after, doing problems is learning consequential things about nature”. There is no real understanding of a symbolic generalization without simultaneous acquaintance with particular examples that is without a given interpre- tation of some phenomenal situations. According to Cartwright, Duhem’s analysis has a lot in common with that of Kuhn. I will now sketch her views on the subject and sub- sequently argue that there is actually a crucial difference between the accounts of the two historians and philosophers of science. Such differ- ence will in turn result highly interesting in the discussion of Kuhn’s views about incommensurability. It is well known that Duhem draws a sharp line between the language of common sense and the language of theory. A common sense gener- alization such as “all men are mortal” is postulated inductively on the grounds of direct observations of facts accessible in everyday life. This is the case because terms such as “man” and “mortal” apply directly to particular cases. Everyday concepts are abstract and general but they can be, according to Duhem, attached unproblematically to individual objects in the real world. A law of physics is, on the contrary, an abstract and symbolic generalization, whose terms cannot be applied directly to individual objects: we cannot see temperature instantiated in a concrete object, just as we see its shape or colour. In order to judge that an ob- ject has a certain temperature we must resort to an act of measurement. It is measurement, as Duhem famously said, that makes possible the translation10 between the abstract and symbolic expressions of physical theory and the concrete circumstances that also the “layman ignorant of physics” would witness while an experiment is being performed.

9[Kuhn 1970a, 189], emphasis added. The fact that Kuhn considers irrelevant whether a concept is acquired “with pencil and paper or in a well-designed laboratory” will play an important role in the next sections. 10It order to avoid confusion, it must be stressed that Duhem uses the term “trans- lation” somehow metaphorically, and not in the more technical sense implied by Kuhn while discussing the notion of incommensurability. Incommensurability and laboratory science 243

According to Cartwright, Duhem’s and Kuhn’s claims can be both accounted for by pointing out that the relation between a symbolic ex- pression and the different cases to which it applies is that of the abstract to the concrete. Just like the abstract moral of a fable is expressed and made intelligible thanks to the description of a concrete situation, an abstract generalization such as f = ma needs more concrete models in order to be understood by students and practitioners of physics. Clearly, there are many different possible models embodying concrete situations that fall under a single abstract description. The question that should be now asked, I believe, is just: how con- crete are the models Cartwright (and Kuhn) refers to? Certainly, not as concrete as Duhem’s common sense facts and descriptions. The following example is sufficient to show this:

I maintain that to say of mass m that it is distance r from another mass M is a concrete description to which corresponds the familiar more abstract 2 description “Mass m is subject to a force of size GmM/r ”. [Cartwright 1993, 268].

What is considered concrete in this case is actually expressed in math- ematical terms and involves a physical concept such as that of mass. Clearly then, the models that render abstract and symbolic general- izations intelligible can still be quite apart from the world of everyday experience. Cartwright is fully aware of this:

Of course, the more concrete descriptions may themselves be abstract when compared to yet another level of discourse in terms of which they can be more concretely fitted out in turn. (. . . ) Models are a long way from the world. [Cartwright 1993, 270].

How then is the actual connection with the world eventually obtained in the case of mathematical physics? How do models relate to reality? That can happen only when an experiment is performed11. The prob- lem of the relationship between the recondite concepts of physical theory and those of everyday experience cannot therefore be resolved simply by distinguishing physical theory from models. A schematic account based on at least three stages must be developed, where the final link with the world is realized by means of experimental practices. Cartwright (who also pays attention to this third experimental level) has excessively stressed, I believe, the analogy between Duhem’s and Kuhn’s views on

11There are indeed other highly theoretical sciences whose hypotheses are not re- lated to the world only with the aid of experiments. 244 Emiliano Trizio the subject. In the following section I will briefly recall some of Duhem’s interesting insights on the relation between theory and experiment. Sub- sequently, I will try to show, on the grounds of a qualified “duhemian” position, that Kuhn has never really put this relation properly into focus when dealing with the problem of how scientific terms attach to nature.

3. Back to Duhem

The problem of relating the symbolic language of physics to nature can be rephrased, borrowing from Duhem, in terms of the possibility to trans- late theoretical facts into practical facts and vice versa. It is true that Duhem draws a distinction between common sense observation and phys- ical experiment; but let us not lose sight of the fact that he also attributes to the results of the experiments belonging to descriptive sciences such as physiology or botany the status of mere reports of concrete facts that need no interpretation in theoretical terms12. The peculiar character of the experiments performed in physics (and up to a certain extent, in chemistry) is due to their being aimed at applying mathematical lan- guage to nature. A theoretical fact is for Duhem, an idealized system fully defined in terms of physical properties, which are in turn expressed in exact mathematical terms, whereas a practical fact is what corre-

12Duhem’s insistence that only physico-mathematical language is responsible for the theory-ladenness of observation is, as it will result clear in the following sections, one of the aspects of his thought that can no longer be accepted. Some of Duhem’s statements about common sense knowledge sound to today’s readers, to say the least, baffling, “The laws that ordinary non-scientific experience allows us to formulate are general judgements whose meaning is immediate. In the presence of one of these judgments we may ask, ‘Is it true?’ Often the answer is easy; in any case the an- swer is a definite yes or no. The law recognized as true is so for all time and for all men; it is fixed and absolute.” [Duhem 1991, 178] (the pages mentionned are the ones of the english edition). The great critic of inductive method doesn’t even question the absolute validity of general common sense judgements, besides that of particular ones! Theories, however, do not exist, according to Duhem, only within mathematical physics, although the term “theoretical fact” is forged by him specif- ically for the latter. Also physiologists develop theories, but the experiments they perform are not infected by them and rest on the direct observation of “a recital of concrete and obvious facts” [Duhem 1991, 147], whose status is very much alike to that of common sense experience, “When many philosophers talk about experimental sciences, they think only of sciences still close to their origins, e.g., physiology or certain branches of chemistry where the experimenter reasons directly on the facts by a method which is only common sense brought to greater attentiveness but where mathematical theory has not yet introduced its symbolic representations.” [Duhem 1991, 180]. Experiments pertaining to those sciences “still close to the origin” involve theoretical presuppositions only when (again) physical instruments are used [Duhem 1991, 183], but clearly this is an exogenous source of theory-ladenness. Incommensurability and laboratory science 245 sponds to it in the real world, which lies before our eyes, the world in which there is no perfect geometrical shape, no point-like particle, no physical magnitude defined at each instant and at each point and, most of all, no exactly quantifiable property; in short, the world accessible to our senses and describable without any knowledge of physics13. It is tempting to think that Duhem is trying to relate objects, as they are directly perceived, with the physico-mathematical modelizations that replace them in the calculation of the theoretician. The layman sees a block of ice (the practical fact), while the physicist “sees” a thermody- namic system subject to certain pressure etc. (the theoretical fact). The famous title of the section opening the chapter of La Théorie Physique in which Duhem analyses the role of experiments in physics, seems to underwrite this interpretation: “An Experiment in Physics Is not Sim- ply the Observation of a Phenomenon; It Is, Besides, the Theoretical Interpretation of This Phenomenon” [Duhem 1991, 144]. The title sug- gests that on one side there are the phenomena, the practical facts (i.e. nature) as they are directly observed, while on the other side there is their interpretation in the language of physical theory. Nevertheless, the examples described in the section show that the real state of affairs is more complicated. It is worth quoting at length the description of one of them:

Regnault is studying the compressibility of gases; he takes a certain quan- tity of gas, encloses it in a glass tube, keeps the temperature constant, and measures the pressure the gas supports and the volume it occupies. There you have, it will be said, the minute and exact observation of certain phenomena and certain facts. Certainly, in the hands and under the eyes of Regnault, (...) concrete facts were produced; was the recording of these facts that Regnault reported his intended contribution to the advancement of physics? No. In a sighting device Regnault saw the image of a certain

13Duhem’s theoretical facts are very much at the same level of Cartwright’s models and Kuhn’s text-book problems: they are expressed in the language of physics, but they are not as general and abstract as either physical theories or physical laws. They differ from models or exercises in that the latter consist of the description of a whole physical situation, whereas the expression “theoretical fact” can be used also to refer just to a part or a single aspect of it, or to temporal stages of its evolution. An oscillating circuit with given characteristics can be the object of textbook exercises and can be a model that helps us to relate electromagnetic theory to the world. A theoretical fact, on the other hand, can consist of a description of the kind “there is here an oscillating circuit of such and such characteristics”, but it can be also “there is an electrical current of three ampere” and even “the current is on”. Finally, theoretical facts must be distinguished from laws and generalizations that Duhem sees as complex summaries of theoretical facts and that, in turn, are classified and summarized by physical theories [Duhem 1991, 22-23]. 246 Emiliano Trizio

surface of mercury become level with a certain line; is that what he recorded in the report of his experiment? No, he recorded that a gas occupied a volume having such and such a value. An assistant raised and lowered the lens of a cathetometer until the image of another height of mercury became level with the hairline of the lens; he then observed the disposition of certain lines on the scale and on the vernier of the cathetometer; is that what we find in Regnault’s memoir? No, we read there that the pressure supported by the gas had such and such a value. (. . . ) [Those values are] abstract symbols which only physical theory connects to the facts really observed. [Duhem 1991, 145-146].

As this passage clearly shows, what the concrete facts really observed amount to is the history of the experimental setting while the experiment is been performed, as it would appear to a layman ignorant of physics. This history is not only that of the objects under investigation, the frag- ments of external reality the experimenter strives to describe in physical terms (in this case, the gas enclosed in a glass tube); it is also that of the actions, instruments and tools that have been deployed in order to bring about the required conditions (Duhem says: “concrete facts were produced”) and to carry out the relevant measurement procedures. It is this “the recital of concrete facts” that must be interpreted with the aid of physical theory, not a chunk of the ready-made phenomenal world, for clearly, a thermometer and its use have nothing do to, by themselves, with the sample of gas. This recital is translated in the report, which in turn provides the basis for stating the results of the experiment. Both the report and the results are stated in an abstract and symbolic language. Duhem’s analysis of the nature of this reformulation in theoretical terms can be schematized in the following way:

1. The sentences in common sense language describing the facts really observed must be replaced by abstract and symbolic judgements. This, in turn, implies that: – the instruments used must be mentally substituted by ide- alizations endowed with physical properties known in an ap- proximate way14. – the actual spatio-temporal region in which the phenomenon under investigation occurs must be replaced in the mind of

14It is while discussing the role of instruments in laboratories that Duhem in- troduces the important notion of type schématique d’instrument (see original ver- sion, [Duhem 1906, 235], unfortunately translated into English as “schematic model” [Duhem 1991, 156], thus somehow hiding the possible link with the classificatory nature of physical concepts and laboratory activities (see next section). Incommensurability and laboratory science 247

the experimenter by a physical system fully defined by all physical properties that, as far as it is known, may turn out to affect in some way the result.

2. The data obtained must be analysed according to the theoretical interpretation of the experiment in order to formulate the abstract and symbolic judgement constituting the result of the experiment.

The theoretical replacement concerning the laboratory as a spatiotemporal region implies, we could say, that the entire world is omitted from the theoretical interpretation of a phenomenon, except for what our theo- ries assert to be relevant, once a certain degree of approximation in the physical description has been set as a target. Having briefly recalled Duhem’s reconstruction of the interpretative moment of an experiment, we can now try to see whether it helps us to better appreciate the nature of the relation between theoretical facts and practical facts and, consequently, that of physical theory to the world.

4. Conceptualization in laboratory science: the dual taxonomy

As we have seen, Duhem refers to this relation as a translation. How- ever his own account invites us to describe it as one of conceptualization or subsumption: physical theory provides a network of concepts that through experimental practices are applied to the world. Talk of con- cepts and their application will help us to highlight the role of practice in laboratory science and its relevance for the doctrine of incommensu- rability. What is essential to this analysis is that it shows us how to recog- nize the peculiar character of the conceptualization provided by physical theory vis-à-vis the ordinary application of observational concepts. Con- cepts of any kind serve the purpose of grouping individuals into classes. They provide a taxonomy of things, events and processes that renders the world intelligible to us. Although it would seem natural to think that physical knowledge develops on the grounds of commonsensical, pre-existing taxonomies, by correcting and refining them in virtue of a rich and highly sophisticated network of concepts which, so to speak, su- perimposes on the previous one, the preceding analysis shows that this is not exactly the case. I refer here to the fact that physical concepts attach to nature only if a whole experimental context is theoretically 248 Emiliano Trizio interpreted. Let us see why this fact makes physical concepts and de- scriptions so different from ordinary ones, by comparing the following two statements:

(1) when the sun rises, the air becomes warmer; (2) if the pressure of a gas battery increases by so many atmospheres, its electromotive force increases by so many volts.

Statement (2) is reported by Duhem as an example of an experiment’s conclusion [Duhem 1991, 148]. Of course (1) can be understood by any competent speaker of English, whereas understanding (2) requires some knowledge of physics; yet their cognitive content remains essentially dif- ferent also for the trained experimenter. Both statements can be tested under the circumstances they describe, but the (practical) facts referred to by (1) are recognized on the grounds of everyday perceptual similarity, while the situation described by (2) can be tested in infinitely different concrete situations that have hardly anything in common in terms of per- ceptual properties15. Perceptual similarities are simply sidestepped by physical conceptualizations. The experimenter in order to control the validity of (2) may adopt several alternative measurement techniques, which require different instruments and procedures. The experimental setting which would be perceptible in the laboratory and the series of manipulations it would undergo would change completely from case to case. The interpretation of a physical experiment I previously men- tioned requires different actions depending on the choice of samples, instruments and tools and even of the place in which the laboratory is situated. Without a careful check of these conditions, without a simul- taneous subsumption of these items under appropriate theoretical types, the required physical description won’t apply at all to what is actually seen and touched. However:

(. . . ) all these diverse manipulations, among which the uninitiated would fail to see any analogy, are not really different experiments; they are only different forms of the same experiment; the facts which have been really produced have been as dissimilar as possible, yet the perception of these facts is expressed by a single proposition: The electromotive force of a certain battery increases by so many volts when the pressure is increased by so many atmospheres. [Duhem 1991, 149].

15This is not only true of physico-mathematical descriptions, for there exist other types of concepts that do not apply to the world in virtue of perceptual similarities standards. What is however at issue here is a comparison between the language of mathematical physics and the language used in basic observational reports. Incommensurability and laboratory science 249

Sentence (1) describes a particular set of facts involving situations which are identifiable on the basis of perceptual similarity and, more- over, identifiable independently one from the other. It is not because you see that the sun is rising that you feel warmer and vice versa. Objects and processes enter sentence (1) one by one, without mutual definition. On the contrary, the experimenter cannot say that the pressure has in- creased by so many atmospheres without holding some beliefs about the manometer (and about many other things) and, conversely, the failure of observing expected phenomena might cast doubts on the reliability of the instruments implemented. New checks may be called for (new prac- tical facts would take place in the laboratory), new systematic errors may be taken into account, and the very fact that an instrument was acting as a manometer, that is, its being an instantiation of an abstract type of instrument, may be questioned. This example clearly illustrates a situation that we could describe with the term co-subsumption: the gas cannot be subsumed under the predicate “having a pressure of x atmo- spheres” if at the same time the instrument used to determine that the value of its pressure is x is not subsumed under the predicate “reliable manometer”. A concept’s extension can be said to consist of an equivalence class of individuals. What we have just seen is that physico-mathematical concepts cannot divide up the world in different classes without a si- multaneous definition of equivalent classes of experiments allowing their applications to the world; thus, physical theory does not provide a static taxonomy of the world, it yields rather an interrelated dual taxonomy of entities and actions in experimental contexts. In a laboratory physical entities cannot be classified if a suitable co-classification of the practical context and of the material items involved does not take place16. Only in this way can we understand in what sense physical experiments may be said to be repeatable. As a series of concrete facts each experiment actually performed is unique and different from any other, but physical theory provides a complex conceptual unification of these series of facts under a single abstract and symbolic description. Only at the level of these abstract descriptions can the methodological condition of repeata- bility be fulfilled: observable regularities play little if any role at all in laboratory science17.

16Popper famously said that in the exploration of reality our theories play the role of new sense organs. I believe this should be said rather of experimental contexts under a theoretical description. An equivalent class of seemingly different experi- ments conceptually unified by a theoretical description constitutes an extension of the cognitive possibilities of our body. 17In an article on the nature of laboratory science, Ian Hacking has maintained 250 Emiliano Trizio 5. Perceptual taxonomies and physico-mathematical taxonomies

We have seen that Duhem introduces a distinction between physics and chemistry on the one hand and more descriptive sciences such as anatomy and physiology on the other. His holism applies only to the former, while the latter relate to the world somehow unproblematically, in virtue of the direct mirroring of external reality provided by naked-eye observa- tion. There is hardly the need to say that we can no longer accept such a sharp cleavage. There is no such thing as a purely descriptive common sense language and the concepts used in ordinary contexts to classify the objects of perception are always theory-laden. Just as a physicist cannot leave his theories outside the laboratory when perform- ing an experiment, a layman cannot utter any judgement about the world without interpreting what he sees in the light of a given concep- tual network. Where Duhem saw a sharp discontinuity, more recent philosophers of science have seen, at best, a continuous range of dif- ferent degrees of theory-ladenness. This fact is clearly highlighted by Kuhn’s treatment of meaning change and incommensurable taxonomies, which is supported by examples taken from episodes scattered through- out the history of science, regardless of the level of abstraction of the theories under discussion and of the degree of sophistication of the ex- perimental techniques involved. Kuhn mentions the shift from Ptolemy’s to Copernicus’ astronomy on a par with the controversy about phlogis- ton or the conceptual changes brought about by Planck’s solution to the black-body problem. He treats all these historical episodes as examples of how the way language organizes experience can undergo more or less radical changes. It really seems that language and experience are no less central to Kuhn’s history-oriented account of knowledge than to the log- that Duhem’s analysis stresses the role of intellectual elements on the grounds that it focuses on the interplay of theories and auxiliary hypotheses, thus neglecting the role of actions and material items [Hacking 1992, 54]. This interpretation is probably motivated by Duhem’s strong emphasis on the theoretical character of the interpre- tations necessary for the use of instruments. My reconstruction should show, on the contrary, that Duhem, although not very explicitly, has taken into account the role of action and material items in experimenting and testing. Clearly, whatever is per- ceived or done can in principle be described and, under this description, becomes part of the host of hypotheses surrounding experimental activities; yet, it remains true that what Duhem’s hypotheses are also about is actions and material items, and that he certainly does not treat laboratory devices as “(. . . ) black boxes, as established devices that generate data which are literally given” [Hacking 1992, 53]. Hacking rightly says that “all action, all doing, all working is under a description” [Hacking 1993, 277], I would add that there is no better way to summarize Duhem’s ideas on the matter. Incommensurability and laboratory science 251 ical reconstructions of scientific activities developed by his predecessors. Certainly, letting Duhem’s crude distinctions go by the board allows us to achieve a more comprehensive perspective on knowledge and to dis- cuss interesting phenomena such as holism and incommensurability also outside the domain of mathematical physics. But does this mean that within a satisfactory account of the way concepts deploy their descriptive power, laboratory activities shouldn’t nevertheless be granted a different status with respect to naked-eye observations? Can’t we look instead for a more fine-grained analysis of the different ways in which scientific con- cepts apply to the world? It is precisely on these grounds that, I believe, Duhem can still teach something to Kuhn. As we have seen, Cartwright has urged that a distinction between ob- servation and theory is needed. It is worth noticing that, in his answer to Cartwright, Kuhn accepts that distinction but he adds some important qualifications:

I agree that the distinction is needed, but it cannot be just that between the “peculiarly recondite terms [of modern science and] those we are more used to in our day-to-day life.” Rather, the concepts of theoretical terms must be relativized to one or another particular theory. Terms are theoret- ical with respect to a particular theory if they can only be acquired with that theory’s aid. They are observation terms if they must first have been acquired elsewhere before the theory can be learned. ‘Force’ is thus theo- retical with respect to Newtonian dynamics but observational with respect to electromagnetic theory. [Kuhn 1993, 246].

This passage renders even more apparent how Kuhn’s point of view is language-centred. A term is theoretical with respect to the theory in which it is embedded and observational with respect to a (presumably) more complicated one, in which the term is nevertheless applied as an antecedently understood one. Clearly what Kuhn has in mind here is, once more, the language/theory learning process. In that process a pre- viously understood vocabulary is necessary for learning new scientific concepts. A term is therefore observational, for Kuhn, if it belongs to a language, which provides the ground for further theoretical develop- ments; the main advantage of this account being that it yieldsa develop- mental notion of the theory/observation distinction. At a certain stage, an individual or a community is endowed with some available dictionary, which of course is theory-laden for it makes sense in the context of the given language/theory in which it had been previously learned. This dictionary happens to be the contingent starting point for “further ex- tension of both vocabulary and knowledge” [Kuhn 1993, 247], but, once 252 Emiliano Trizio the process of enlarging theories and dictionary get started, it becomes observational with respect to some new sets of terms. In short, there is no static, a-historical distinction between observational and theoretical terms, no original linguistic starting point, which lays stable foundations for the edifice of knowledge. I believe that this solution can be accepted if what we are after is to understand how language is learned and how terms belonging to succes- sive theories relate to each other, but it fails to provide an account of how different types of terms attach to nature. Terms such as “red” or “wood” on one side and “force” or “electrical resistance” on the other, in spite of their being all theory-laden in virtue of their embeddedness in a language, do have an intrinsically different status, for the former can and normally are applied on the grounds of simple perception, whereas the latter are concepts whose application requires acts of measurement. No developmental process, no paradigm shift, no new acquisition of knowl- edge and vocabulary can efface that difference or swap the roles of the two families of terms, for that difference is not grounded on language or theory, but in the different activities needed to apply them to the world. Indeed perceiving and measuring are essentially different performances of the knowing subject. To accept this does not imply a vindication of the duhemian cleavage between the uncontroversial but vague common sense facts and the precise but hypothetical theoretical facts, nor to resort to a kind of carnapian divide between the class of theory-free observa- tional terms and the class of theoretical terms logically connected to the former via appropriate bridge principles18. I agree that all language is theory-laden and that also observational reports are fallible and relative to beliefs held at a certain developmental stage; nevertheless, I insist that there is a sharp difference in the way in which those terms or descrip- tions are attached to nature. A term like “quantity of heat” will never be observational in the way a term like “tree” is and this is the case for any term or taxonomy that, although not quantitative in itself, requires acts of measurement for its application19. At a particular historical stage, we are given a certain contingent conceptual network and we would be wrong in trying to split its vocabulary into an observational and a the-

18A succinct exposition on Carnap’s ideas on the subject, which also pays attention to its evolution, can be found in Carnap’s intellectual autobiography (see especially § 13), published in [Schilpp 1963]. A comprehensive reconstruction and a critical appraisal of the debate concerning the theory/observation dichotomy within logical empiricism can be found in [Parrini 2002]. 19Venturing a long way outside the domain of physics, we find that a science like palaeontology is a source of examples of this kind (that are frequent also in physics, see section 7). Incommensurability and laboratory science 253 oretical part on the basis of a linguistic analysis, whether one (like that of Carnap) that purports to identify an intrinsic, unchanging distinction or one (like that of Kuhn) that aims at drawing theory-dependent and shifting dividing lines. What is needed instead, is an investigation of the various activities underlying the application of the conceptual terms (note that application does not reduce to learning but see further on this point) and an analysis of the intrinsic characteristics of these activities. The comparison between the sets of terms that must be applied in order to test sentences (1) and (2) of the previous section respectively should be interpreted in this way. The common sense taxonomy (or conceptual cluster):

(a) {sun, sunrise, air, warmth} is different from the physico-mathematical taxonomy (or conceptual cluster):

(b) {pressure; electromotive force; increase in pressure by so many at- mospheres; gas battery; increase in electromotive force by so many volts; relevant instruments; tools; conditions of the laboratory; ac- tions of the experimenters; etc.} because the activities needed to apply the concepts belonging to (a) amount simply to acts of perception, whereas those involved in the ap- plication of concepts such as “pressure” and “electromotive force” are, be- sides perceptions, complicated theory-laden instrumented actions aimed at measuring physical quantities. Those actions are therefore co-inter- preted by the physico-mathematical taxonomy, which, for this reason, deserved to be called dual 20. This explains why the concepts belonging to (a) do not refer to the acts of perceptions, nor to the sense organs needed to apply them, while in taxonomy (b) the actions and material items of the experimenter are taken together with the description of the physical properties and events. Physical theory, as Duhem says, unifies conceptually experiments that have nothing visible in common beyond what belongs necessarily to any structured perception of objects and properties, which implies that the entities physical theory describes are classified if and only if the experimental contexts that reveal them are classified in turn. It might be objected that also the application of observational terms requires the fulfilment of some conditions concerning the context of the

20All physico-mathematical taxonomies are dual, but the converse needs not be true. 254 Emiliano Trizio application. In order to decide whether what I see is a cat or a small dog, I need to get sufficiently close to the animal, I must have a well func- tioning perceptive apparatus, I must not be hallucinating or under the effect of drugs etc., the objection would then continue that those con- ditions are omitted from everyday observational reports, even though they must be fulfilled for the reports to be reliable and to count as valid applications of terms and descriptions to reality. Does this objec- tion show that every taxonomy deserves to be called dual? Let us see. The reason why concepts referring to the act that allows the application of ordinary observational terms, are normally omitted is precisely that they would be in most cases identically the same. Observation terms are defined precisely by their being immediately applicable on the basis of that particular kind of act, which is unaided, normal perception. Our ready-for-use dictionary of objects, properties and states of affairs is not split in different sets in turn linked to specific conditions of application. In order to recognize everyday objects and their properties some con- ditions defining normal, reliable perception must be fulfilled and those conditions somehow contribute to the very meaning of the word “ob- servation”. Observation terms are, for a given speaker or community, those which can be readily used on the basis of simple perception. It is not the case that to the various taxonomies of cutlery, pets, home tools or road signals there correspond specific sets of concepts defining the conditions of their applications. What is peculiar to each of these taxonomies and makes it different from the others consists only in “ob- jective terms” referring to reality, not in interrelated “act terms” that define appropriate conditions of application of the former. As we have seen, the contrary holds for physico-mathematical taxonomies. They contain “objective parts” composed by descriptive terms purporting to refer to the world and “experimental parts” which are highly interrelated to the former via the intermediary of physical theory. Each objective physico-mathematical conceptual cluster is a semi-dual taxonomy that demands a specific “experimental counterpart” for its proper application. It requires, therefore, the definition of a particular set of those “instru- mented cognitive activities” that we call “experiments”. This is not the case for observational taxonomies that hence cannot be called dual in a non-trivial sense. Let us underline again, in conclusion, that the distinction between (a) and (b) is non-developmental, just as much as the difference between bare perceiving through the sense organs and performing instrumented manipulations in order to apply the language of mathematics to the external reality. It is true that measurement practices can develop only Incommensurability and laboratory science 255 on the grounds of a pre-existing perceptual activity; but this is not the kind of “developmental character” that Kuhn refers to, and which is at issue here. According to Kuhn, a term like “electrical resistance” can be theoretical at a certain developmental stage and become observational (just like “tree”) at a later one. I argue instead that this is impossible because of the physico-mathematical character of the concept “electrical resistance”. As we shall see, Kuhn’s failure to notice this kind of distinction and its non-developmental character has repercussions on his description of the role of paradigmatic examples in the way scientific terms apply to the world.

6. Textbook problems and experiments

Can we really say that by solving paradigmatic textbook problems stu- dents learn to relate physical symbolic expressions to reality? In the light of the preceding considerations, we can say that an affirmative answer would be rash. A physics problem is still a purely theoretical exercise in which physical quantities appear as given from the outset. Even when concrete objects (such as a pendulum) are mentioned, their property are fully defined in mathematical terms, moreover each problem consists of the description of a “physical micro-drama” (such as a collision or the tra- jectory of a ball) which takes place in a world purified by all disturbing factors, a world reduced to a suitable physical description (see section 3). As Cartwright says (see section 2), “models are a long way from the world” and we need to step into a laboratory to actually see how to connect an abstract model (and, indirectly, the physical theory behind it) to reality. What was immediately given in the textbook suddenly be- comes the result of painstaking investigations. The physical quantities are not waiting for us to use them in our calculations; they are to be found with the aid of some instruments, instruments that are normally omitted from the description of the problem. Moreover the elimination of disturbing factors cannot be simply postulated, it must be achieved. This is why students can often be very talented for solving problems, and yet feel completely lost in a well-equipped laboratory where they have a hard time recognizing that what happens before their eyes is the situation described in the textbook. Kuhn’s account does not focus on this point. In various occasions he equates learning through problems with learning in the laboratory, for in both cases, according to him, it suffices to notice that students are exposed to some exemplars and that this allows the application of the theory to the real world. 256 Emiliano Trizio

Sometimes the exemplars discussed by Kuhn include standard mea- surement instruments such as galvanometers and manometers, but the analysis of their role does not lead to an acknowledgment of their priv- ileged function with respect to theoretical learning in the application of physical language to reality, nor does Kuhn introduce the idea of a hierarchy of increasingly concrete and quantitatively defined exemplars. Had he done so, he would have probably paid more attention to the fact that during an experiment, physico-mathematical terms must be applied not only to the world, but also, at the same time, to the instrumented activities of the experimenters. In this way he would have appreciated the peculiar character of dual taxonomies with respect to perceptual ones. Similarly, in the Postscript some effort is made to distinguish the literal sense of the word “seeing” that is involved, for example, in ancient astronomy, from the “metaphoric” one that Kuhn adopts to account for complex experimental activities necessitating the use of instruments; but no satisfactory characterisation of the difference is actually provided. We can even say that Kuhn’s later insistence of the language-dependence of theoreticity marks in some way a step backward with respect to some programmatic statements that can be found in the Postscript and in the article Second Thoughts on Paradigms [Kuhn 1974, 459-482], [Kuhn 1977, 293-319]. Why is Kuhn so reluctant to focus on the specificity of laboratory activities? I believe it is because he conflates two different processes: learning or understanding a scientific term (or theory) and attaching it to nature. Let us try to clarify this point. Certainly, as Kuhn says, in order to learn classical mechanics, we need to have in mind some ex- amples of concrete mechanical systems. Nevertheless, various degrees of acquaintance with such examples must be distinguished. As Cartwright has noted (see section 2), we may find a series of increasingly concrete descriptions of an abstract, physical situation. Eventually, the desire for concreteness will inevitably lead us into a laboratory, where all the prob- lems that have been mentioned will be waiting for us. Yet, if what we are after is only to learn and understand the theory, we can be content with a description of the physical situation, which occupies an intermediate position on the concreteness scale. It is at this level that most of the teaching, learning and communication in physics takes place. Classical mechanics can be understood without any laboratory session just with the aid of some more or less defined concrete situations that the teacher needs only to describe to the students, often in qualitative terms. The teacher, for example, can easily introduce the main ideas of the theory of collisions by referring to the well-known example of the billiard. He or Incommensurability and laboratory science 257 she can then torment the students with all kinds of textbook problems, where mathematics will have the predominant role. Lecturing in front of a real billiard may have some pedagogic effect, but it won’t change the nature of what is being done, that is, teaching and understanding. If on the contrary, we wished to test the mathematical predictions of the theory of collisions with a high degree of accuracy on the very billiard before us, we would immediately find ourselves lost in a duhemian jun- gle of instruments, careful checks and auxiliary assumptions. It is only at this further stage that the mechanical concepts would authentically be applied to the world and not in the bare linguistic activities in which they are taught and learned 21. Theoretical physics provides us with other interesting examples. The Higgs boson is a particle postulated by the standard model of particle physics, which has not yet been detected. Therefore the concept “Higgs boson” has never been really applied to nature. Nevertheless, even if that particle happens to be found, the very event of its identification won’t add much to the understanding theoretical physicists have of the standard model. Could one really maintain that, as long as physicists are not trained experimenters as well as skilful problem-solvers, they do not really un- derstand the theory? I suspect that today’s theoreticians who, in the laboratories where their theory are being tested, often feel very much like a duhemian layman “ignorant of physics”, would be rather upset by an affirmative answer.

7. An example of dual taxonomy

In this section I will illustrate the notion of dual taxonomy by means of a relatively simple example. The conceptual structure of modern physical theories is often far too complicated to be visualised with the aid of simple diagrams. As the degree of complexity cannot but increase if the experimental side is also taken into account, in my example I will only consider a small fragment of an already fairly robust taxonomy, namely that of crystalline lattice structures. Within the class of lattices whose unit cell has a cubic shape, we find the subclasses of the simple cubic lattices (S.C.), the face-centred cubic lattices (F.C.C.) and the body-centred cubic lattices (B.C.C.). As it is well known, there are experimental procedures involving the diffraction

21Authentic application does not imply the adequacy to a mind-independent reality, but simply the presence of conditions that make possible the application of a term. 258 Emiliano Trizio of X-rays that allow the determination of the lattice structure of various substances as well as the corresponding unit cell dimensions. In general, a suitably prepared specimen of the crystal under investigation is placed in a beam of monochromatic X-rays. The resulting diffracted beams produce a diffraction pattern, which is recorded on a strip of film. The study of the diffraction pattern provides the required information about the lattice structure. In the diagram given at the end of the present paper, the boxes in the vertical column represent the types of cubic lattices. For simplicity the subsumption of only one element (copper) under the corresponding type of lattice structured is represented. The boxes representing objective properties and entities (the objec- tive parts of the dual taxonomy) are drawn with continuous lines. The big arrow represents the subsumption of the element copper under the predicate “having a face-centred cubic lattice”. The subsumption occurs if and only if an experiment is performed, which belongs to the class of equivalence of all possible experiments leading to the same conclusion (conceptually unified by physical theory). This class of equivalence can in turn be divided in types of experiments, thus giving rise to the ex- perimental part of the dual taxonomy. A box drawn with dashed lines within the arrow represents each different type of experiment. We can imagine that in order to “reach” the box of F.C.C crystals, the element copper would have to “jump” into one of the boxes contained in the ar- row. That is: for copper to be subsumed under the predicate “having a F.C.C. lattice structure”, a sample of copper must be analysed with an experimental procedure in turn co-subsumed under a type of theoreti- cally acceptable experiments. It is certainly true that the specification of the experimental part of a dual taxonomy is highly problematic. For our purposes an experiment is defined as the set of all practical and intellectual operations necessary to achieve the final result from the choice, preparation and use of the experimental setting to the analysis of the data. There are clearly sev- eral ways in which the different types of experiments can be defined. In our example, the choice of the source of X-rays would be considered as an important discriminating factor and so would be the procedure used to render the radiation monochromatic and to measure its wavelength. But, would the kind of film or the method of development adopted be considered as defining different types experiments or would they sim- ply determine minor distinctions between subtypes22? As a matter of

22In general such a classification will of course admit a complex branching of types of experiments into more and more precisely defined subtypes. In the diagram this hierarchical structure has been omitted for simplicity. Incommensurability and laboratory science 259 fact, no experiment can ever be completely described and in general, no experiment can be the exact repetition of another one: a great deal of tacit knowledge, of the kind students acquire only by imitating their teachers, contributes to determine the way an experiment is done and interpreted. Tacit ceteris paribus clauses intervene to wipe out the un- manageable number of little details that we deem without effect on the result. In short, the experimental part of a dual taxonomy is doomed to remain, up to a certain extent, sketchy and incomplete and some vague- ness will inevitably affect the boundaries between types and subtypes of experiments. Difficult though it may be to fully specify taxonomies of experiments, it remains true that the description of the experiment is logically necessary for the application of physico-mathematical concepts to reality. It must be stressed that, although a predicate such as “having a F.C.C. lattice structure” is not by itself the result of an act of measure- ment, it can only be applied if several physical quantities are determined (the wavelength of the monochromatic beam of X-rays, the exact posi- tion of the specimen in the camera, etc.). Moreover, as I have already said, experiments of the kind just described are normally made in order to determine also the unit cell dimension of the lattices, which can be derived by the exact position of the reflections constituting the inter- ference pattern. It would be possible to take into account these further determinations in the diagram of the dual taxonomy, but at the price of increasing its complication. Each box in the vertical column would be split in an enormous number of little boxes corresponding to predicates of the kind “having a F.C.C. lattice structure with unit cell dimension 4.049 Å”, “having a F.C.C. lattice structure with unit cell dimension 4.056 Å” etc. The number of such predicates would depend on the degree of precision that our experiments allow us to attain. Aluminium, for in- stance, would be connected to the little box corresponding to the first of the just mentioned predicates by an “experimental arrow” containing the class of equivalence of all experiments whose result is compatible with the correct value. The reason why, normally, predicates of this form are not considered “taxonomic” (in the strict sense of the word) is easy to understand. From a logical point of view there is nothing wrong in considering a crystal “having a F.C.C. lattice structure with unit cell dimension 4.049 Å” as a kind of crystal “having a F.C.C. lattice structure”. However, it is clear that most of the classes corresponding to such predicates would be empty, for they far outnumber the existing elements and substances. As taxonomic kinds are normally introduced to describe in a simple and compact way a multiplicity of individuals, 260 Emiliano Trizio the ordinary quantitative determinations we encounter in physics do not have, in general, a classificatory function in the traditional sense. Yet it remains true that, in principle, also physico-mathematical values belong to the taxonomic lexicon of a theory: a force of 3 newton is a kind of force23. This fact is of crucial importance for understanding the common features shared by Kuhn’s and Hacking’s versions of incommensurability.

8. The ostensive character of theories

Yet one may think that something has been lost on the way. It may seem hard to deny that after all, physical concepts can and often are applied to the world also outside the laboratory. While holding a mug full of boiling hot coffee, we may say that some quantity of heat is being transmitted to our hand, and while seeing some sparks on a conductor, we may speak of electrical currents, electrostatic potentials and of the air’s dielectric coefficient. Indeed physical theory is often used to explain a huge variety of phenomena that take place before our eyes. However, different types of application should be distinguished. Just as learning can proceed with the aid of some more or less concrete descriptions, the application of physical theory to actual situations admits degrees of fulfilment 24. A sketchy explanation of an electrical phenomenon in qualitative terms cannot be equated with the precise quantitative determination of it that can take place in a laboratory. Physics can be taught in classrooms and used to formulate sketchy explanations or qualitative predictions in the “open air”; but it can be properly tested only through careful experiments. Having said this, it must be added that the analysis of this problem can be satisfactorily carried out only by taking into consideration the role played by ostension in physics. Especially in his later works, Kuhn’s analyses of the function of ex- emplars in theory learning have heavily relied on the role of ostension. He takes ostension to be a procedure by which a particular object or situation is exhibited in order to explain the domain of applicability of a concept, without intending it as a radically pre-linguistic activity that would enable us to point at objects before any conceptual vocabulary is available (an antecedently understood vocabulary is, according to him, a necessary condition of theory-learning). The exhibits or exemplars

23From a logical point of view quantitative determinations are taxonomic in char- acter in the strict sense defined by the “kind of” relation. Hence they belong a fortiori to the more loosely defined taxonomies that are at issue in this article. 24The term is borrowed, with some licence, from husserlian phenomenology. Incommensurability and laboratory science 261 have precisely the function of defining the similarity standards the stu- dents must acquire. This explains why a single ostensive episode never suffices to make out the meaning of a concept25 and why ostension is always in some sense theory-laden: Ptolemy would point at the sun and at Jupiter in various occasions, he would remark their changing posi- tions in the sky and would thus illustrate his concept of planet; Volta would draw or build a battery and then point at want he took to be an electric cell, etc.26. Kuhn’s analysis is again both interesting and con- vincing but it has the already mentioned shortcoming of treating on an equal footing examples of conceptual changes occurred from the time of ancient astronomy to contemporary mathematical physics. Actually, he intends to give a language-based account of the meaning of kind terms in general where the conceptual couple cat/dog is mentioned along with conductor/insulator and planet/satellite. On the contrary, if the role of ostension is to be clarified, some attention must be paid to the different categories of objects and properties a given theory is about. Ancient astronomy for instance, is a theory of a very peculiar char- acter for it refers to the behaviour of a particular set of visible objects: the celestial bodies. From the point of view of modern science, Ptolemy didn’t really develop a general theory, but an ad hoc model of a sin- gle complex system whose elements are identifiable through naked-eye observations (however complex they might be). The decisive turning point didn’t come with Copernicus but with Newton. It is only in the framework of classical mechanics that the solar system itself is replaced by an ensemble of mutually interacting masses whose behaviour is described by abstract laws. The resulting taxonomy is already physico-mathematical and, hence, dual. From the point of view of the domain of the theory, the change could not be more radical. The theory of gravitation is about the behaviour of masses, whether in the sky or elsewhere, and the very existence of the solar system (and even that of the fixed stars) is irrelevant to its validity. As long as we can identify objects endowed with mass, Newton’s theory will be applicable. Clearly then, the role of ostension must have been consequently modified and the duality of the taxonomy will play an important role in the identification of relevant empirical situations. A concept that applies to direct visible objects, like “planet” for Ptolemy, is certainly more easily definable by means of ostensive procedures than

25Actually no finite set of ostensive episodes can suffice for the purpose. Meanings are always, in a sense, unfinished. 26Kuhn also mentions the importance of examples taken from the contrast set of concepts. 262 Emiliano Trizio the abstract and mathematical notion of “mass”. That is why complex exemplars are needed involving measurement instruments [Kuhn 1989, 66-74].

The theories developed along the history of science have generally become more and more abstract and mathematical, thus determining a growing role for dual experimental taxonomies with decreasing ostensive character. Newton’s theory, or the theory of heat have still a phenomenal side that we could call in a loose way ostensive, for they refer to classes of objects or facts that belong also to common sense knowledge. With electromagnetism, this ostensive character has become even weaker. Fi- nally, Twentieth Century particle physics has produced theories that do not refer directly in any way to something that can be observed. Their dictionary does not contain any term that belongs to common sense knowledge nor that is easily related to it. With respect to them, even Newtonian talk about masses seems after all to be referring to something open to our gaze. We cannot point at an object or event and be sure that what we are seeing has something to do with the predictions of the standard model of particle physics, for it is only background knowledge that can tell us if and when a pattern of observable facts embodies a model of the theory. The price to be paid for enriching our knowledge with extremely abstract and general theories lies in their remoteness from every-day observation.

Let us go back to the problem of the application of theoretical de- scriptions outside the laboratory. The idea is the following: the more a theory is endowed with ostensive character, the more it can be applied, although often in a loose and qualitative way, outside an experimental context. As science progresses, the role of ostension decreases and the gap between learning/understanding/theorizing on one side and exper- imenting on the other becomes bigger. Kuhn’s exemplars usually refer to stages of the history of science during which that gap is not yet so dramatic as to render this fact evident.

Kuhn himself, in an article on the function of measurement in physics, situates a second scientific revolution between 1800 and 1850, at the time in which physics became fully mathematical [Kuhn 1961, 220]. Duhem writes after that revolution and has clearly understood some of his most relevant epistemological consequences. Incommensurability and laboratory science 263 9. Conclusion: Incommensurability and laboratory science

Let us reconsider the notion of incommensurability in the light of the preceding considerations. A passage of Kuhn describing the changes that taxonomies undergo during scientific revolutions will serve as the starting point of the discussion:

When such a redistribution of objects among similarity sets occurs, two men whose discourse had proceeded for some time with apparently full un- derstanding may suddenly find themselves responding to the same stimulus with incompatible descriptions or generalisations. Just because neither can then say, “I use the word ‘element’ (or ‘mixture’, or ‘planet’, or ‘uncon- strained motion’) in ways governed by such and such criteria,” the source of the breakdown in their communication may be extraordinarily difficult to isolate and bypass. [Kuhn 1970b, 173] (emphasis added). Here again we find examples taken from different theories, regardless of the stage of the history of science to which they belong. This is not, however, what I intend to stress. Rather, I would like to focus on the fact that Kuhn treats incommensurable taxonomies as conceptual net- works that cut up differently a common fund of sensory stimulations. The analysis carried out in this paper shows that this account of incom- mensurability can be applied to the shift from Ptolemaic to Copernican astronomy, or to other episodes involving theories with a strong osten- sive character (section 8), but it need not be the correct account of incommensurability in laboratory science. Certainly, also in sophisti- cated mathematized sciences, it may happen that scientists belonging to rival schools are led to describe the same observable situation with different concepts, but this will rather be the exception than the rule. As we have seen, in a highly developed laboratory science, what is really observed during an experiment is replaceable in virtue of physical theory with items that have hardly anything visible in common (section 3). Dif- ferent experimental settings and procedures are conceptually unified at a theoretical level by a dual taxonomy (section 4). Therefore two rival schools of physicists may accept different dual taxonomies that define distinct classes of equivalence of experimental settings and procedures. In this case the experimenters belonging to the two schools would not be exposed to the same stimulations, for their experiments would look different also to the layman “ignorant of physics”. Incommensurability would take a different and more radical form. It might be objected that after all, the adherents of one school could in principle step into the laboratories belonging to the other and try 264 Emiliano Trizio to understand and describe what happens there in the language of their theory and vice versa. In this case, it might seem that the situation would again be that envisaged by Kuhn: a common fund of sensory stimulations (in this case, those relative to the two sets of laboratory items) are interpreted in a different way in the light of two rival paradigms. It would seem that we could therefore hold on to the kuhnian idea that radical scientific change can be characterised, also in the case of laboratory science, as a change in the way language organizes experience. The answer to this objection can be given by taking into account the peculiar structure of dual taxonomies. As we have seen (sections 5 and 7), a dual taxonomy has an objective and an experimental part. Now, as the diagram of section 7 intuitively illustrates with the graphic differenti- ation between static and dynamic classificatory arrays, what is classified by these two different parts has a specific logical and ontological status. The experiments are not elements or parts of the one world that both schools of physicists seek to understand, in the way objects, properties and processes classified by the objective part of a dual taxonomy are pur- ported to be. They are not natural phenomena “to be saved”, belonging to the explanandum of all rival theories whose adherents strive to render complete. Certainly, any experiment has a material or phenomenal side that demands an explanation of some kind, but, as we have seen, its cognitive relevance for a given theory is dependent upon the theoretical interpretation that the experimenter attributes to it. After observing the experiments that are performed by a rival school of physicists, one could simply be led to consider them as theoretically irrelevant for the actual controversy or even to disqualify them as valid experiments. For instance, disagreement over the shielding of the laboratory, the calibra- tion of the instruments, the treatment of the noise in the analysis of data can determine different views about what counts as a valid experiment and what counts instead as a meaningless series of manipulations. In his last works Kuhn does not seem to stress the role of sensory stimulations. Hopefully this is due to a gradual departure from the nat- uralism that lurks behind his epistemology. However, reference to stim- ulations is unnecessary for his account of incommensurability and for the objections to it that have just been presented. Two contemporary rival theories with a strong ostensive character certainly share a basic vocabulary that can play the epistemological role of “the same stimulus” mentioned in Kuhn’s last quotation. This shared vocabulary can pro- vide the ground for the comparative assessment of the two theories27.

27See [Soler 2003] where it is underlined that, if the rival theories in question are not contemporary, the “common observational vocabulary” belongs to a meta- Incommensurability and laboratory science 265

As the ostensive character decreases, the basic vocabulary available for comparison becomes thinner or even empty and the sharing of measure- ment instruments and procedures will instead play the predominant role in the comparison. The extreme situation in which two rival theories are supported by disjoint sets of measurement procedures is precisely that described by Hacking and named “literal incommensurability”. Hacking, as we have seen (section 1), treats separately this kind of incommensurability from the one that concerns the relation between taxonomies pertaining to rival theories. The aim of my analysis has been to show that these two kinds of incommensurability can be accommodated in an enlarged taxonomic formulation that takes into account the competing roles of ostension and dual taxonomies in the way theories refer to the world. The central idea of this enlarged taxonomic version can now be introduced: Incommensurability results, in general, from a deep transformation of the taxonomy pertaining to a theory, where the term “taxonomy” can refer both to dual taxonomies and to more descriptive ones. In the case of laboratory science, this transformation implies the replacement of a dual taxonomy with a new, incompatible one28. The classical example of lexical incommensurability provided by Ptolemy’s and Copernicus’ astronomies and the examples of literal in- commensurability proposed by Hacking and Pickering refer to theories that are extreme, opposite cases within an ideal classification of theories with respect to the strength of their ostensive character and the inversely proportional duality of their taxonomies: the difference between the two apparently incompatible types of incommensurability is only one of de- gree. The experimental part of the taxonomy pertaining to descriptive sciences is often almost trivial, whereas that of contemporary physics is hypertrophic29. Once reconsidered in this way, therefore, also Hacking’s literal incommensurability can be seen as a case of taxonomic incom- mensurability. The situation he envisages is one in which successive theories differ radically not only with respect to the objective part of their dual taxonomies, but also with respect to the experimental part. The objective part would consist of physico-mathematical predicates: ei- language developed by the historian of science, a meta-language that is not theoretical with respect to the incompatible assumptions of the two theories. The common observational sentences thus introduced need not have actually been uttered by the adherents of the two paradigms. 28In what way the degree of incompatibility of two dual taxonomies should be evaluated is a problem that I will not discuss here. 29This is, I believe, the way in which Duhem’s distinction between different types of sciences should be rephrased. 266 ther physico-mathematical values, or predicates applicable only on the basis of measurement acts. The experimental part would instead consist of types of laboratory practices and measurement procedures ordered in equivalent classes allowing the application to reality of the correspond- ing elements of the objective part. Note that considering the results of measurements as descriptive predicates belonging to the objective part of the dual taxonomy is essential to this taxonomic reformulation of lit- eral incommensurability (see end of section 7): measurement procedures are conceptualizing procedures. Finally, let us not lose sight of the fact that Hacking has considered an extreme situation. Less dramatic cases, in which two competing theories share some elements of the objective and of the experimental part of their dual taxonomies are more likely to occur. Kuhn has often urged that:

(. . . ) men who hold incommensurable viewpoints be thought of as members of different language communities and that their communication problems be analyzed as problems of translation. [Kuhn 1970b, 175].

In the light of the preceding analysis, it can be maintained, I believe, that this account of incommensurability is too narrow. A scientific com- munity cannot be seen, in general, simply as a language community; it must be characterised also in terms of the kinds of experimental contexts and practices through which its theories are applied to the world. After a scientific revolution, scientists do not just “tell a different story” about the world, they also modify their experimental practices and develop new technical and conceptual means for interacting with reality: mod- ern science is a cognitive enterprise to which both language and practice are essential30. It is with respect to the complex interplay of these two elements that a role for the problematic of translation in the discussion of radical scientific change still needs to be found.

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Hanne Andersen Martin Carrier Dept. of Medical Philosophy & Clini- Universität Bielefeld cal Theory Abteilung Philosophie University of Copenhagen Postfach 100 131 Panum Institute D-33501 Bielefeld Blegdamsvej 3 [email protected] DK-2200 Copenhagen N [email protected] André Coret LPHS Archives Poincaré Aristides Baltas 23 Bd Albert 1er Physics Department 54015 Nancy Cedex National Technical University [email protected] Zografou Campus Athens 157 80, Greece Soazig Le Bihan [email protected] LPHS Archives Poincaré 23 Bd Albert 1er Michel Bitbol 54015 Nancy Cedex CREA [email protected] 1, rue Descartes 75005 Paris Léna Soler [email protected] LPHS Archives Poincaré 23 Bd Albert 1er 54015 Nancy Cedex [email protected] Alexander Bird University of Bristol Department of philosophy Emiliano Trizio 9 Woodland Road Université Paris X Nanterre Bristol BS8 1TB 200, rue de la République Angleterre 92001 Nanterre Cedex [email protected] [email protected]