ONTOLOGICAL, EPISTEMOLOGICAL, AND METHODOLOGICAL POSITIONS James Ladyman INTRODUCTION This chapter summarises various important ontological, epistemological and methodological issues in the philosophy of science. Ontology is the theory of what exists and is the foremost concern of metaphysics, which is the study of the most fundamental questions about being and the nature of reality. Ontological issues in the philosophy of science may be specific to a particular special science, such as questions about the ontological status of biological species, or they may be more general, such as whether or not there are objective natural kinds. In the history of science ontological issues have often been of supreme importance; for example, whether or not atoms exist was a question that occupied many scientists in the nineteenth century. In what follows, some fundamental questions of ontology are discussed, some of which, such as those concerning laws of nature, are also ad- dressed in analytic metaphysics. A number of these issues also relate to debates in the foundations of physics about the ontological implications of our best physical theories. Readers who wish to know more about the philosophy of space and time and the nature of matter and motion should consult the companion volume to this on the philosophy of physics. Epistemology is the theory of knowledge and as such is concerned with such matters as the analysis of knowledge and its relationship to belief and truth, the theory of justification, and how to respond to the challenge of local scepticism, say about the past, or global scepticism, which suggests that there is no knowledge. The particular epistemological problems raised by science mostly concern induc- tive inference, since it is widely accepted that substantive knowledge of the world cannot be obtained by deduction alone. The most fundamental such problem is to explicate the relationship between theory and evidence. There are also epistemo- logical issues that only arise when we reflect on the status of unobservable entities posited by our best scientific theories. Finally, methodology here means the theory of the scientific method. Is there a single such method for all the sciences, and if so what is it? How much should we expect the theory of the scientific method to help with the progress of science? Is the scientific method fixed, or does it change over time? Handbook of the Philosophy of Science: General Philosophy of Science - Focal Issues, pp. 303– 376. Volume editor: Theo Kuipers. General editors: Dov M. Gabbay, Paul Thagard and John Woods. c 2007 Elsevier BV. All rights reserved. 304 James Ladyman There is obviously a good deal of overlap between the areas discussed in this chapter. For example, accounts of scientific methodology may have implications for the epistemology of science, and vice versa, and the epistemological issues of whether we ought to be scientific realists has a lot of bearing on whether science can help us address ontological issues. There are vast literatures on all these issues and I have offered some advice about further reading that should help the reader find their way into the subject. 1 ONTOLOGICAL POSITIONS (I) Natural Kinds We divide the world up into individuals and then we class many individuals to- gether in kinds. Hence, we distinguish between horses and donkeys, gold and silver, apples and pears and so on. One of the main concerns of science is to sys- tematically classify natural phenomena and substances into kinds. A system for dividing things into kinds is called a taxonomy. The progress of chemistry, biology, physics and all the sciences is in part the history of a series of re-classifications, and refinements and reinterpretations of existing classifications. For example, in chemistry the kind acid has evolved from the rough notion of a liquid that would react with a base, such as a metal, and produce a salt and water, to the heavily theoretical idea of a chemical that can donate a hydrogen ion; in biology the liv- ing world is no longer divided into plants and animals, rather there is a complex taxonomy of phyla, kingdoms, groups, families, genii, and species; and in physics there have been several taxonomic revolutions from the Newtonian idea of a world of corpuscles and forces, through the late nineteenth century heyday of fields, and into the taxonomy of the four fundamental forces and their associated quantum fields and particles. Nonetheless, there is usually a large degree of retention of taxonomic structure between successive scientific theories. So for example, con- temporary chemistry still classifies as acids the most important acids known in the age of alchemy. A fundamental ontological question is whether taxonomy is a matter or discov- ery or invention, or, in other words, whether there are any objective natural kinds. It is often taken for granted that there are in the case of the natural sciences, but there has always been controversy about whether kinds picked out by the human sciences are objective, or whether they reflect the values of particular societies to which the science and scientists in question belong. For example, there is a consid- erable amount of contemporary debate about whether psychiatric classifications are objective. The idea of objective natural kinds in biology was also cast in doubt by the development of the theory of evolution by natural selection. Species came to be seen as historically contingent and defined by ancestry relationships rather than by morphology. Even when it comes to physics, there are those who deny that the natural kind distinctions it makes are objective rather than pragmatic or socially determined (see the section on Truth below). Ontological, Epistemological, and Methodological Positions 305 In the history of philosophy, questions about natural kinds are closely related to the issue of essentialism because it is often thought that all the members of a kind possess some properties necessarily, and that these properties are characteristic of the kind in question. The idea is that some of the properties of some particular object, are properties that it couldn’t lack without being a different kind of thing. For example, a piece of copper could be a different shape, but it could not fail to be a good conductor of electricity. The modern debate about natural kinds begins with John Locke’s critique of Aristotelian essentialism and the former’s distinction between real and nominal essences. Take gold: the nominal essence is the collection of ideas associated with the word gold, such as those of metallic, yellow, malleable and so on. Locke argued that whatever was the real essence, and he thought it would be some kind of characteristic microstructure, could not be known with any degree of certainty. Contemporary science has restored the faith of many philosophers in natural kinds and essences because our understanding of the chemical elements in terms of the periodic table seems to give us knowledge of the microstructure responsible for their sensible properties? Gold is characterised precisely as that atom that has 79 protons in its nucleus (an atomic number of 79). It is not only elements but also compounds that are often thought to have essences revealed by science. For example, it is widely said among philosophers that the essence of water is H2O. Clearly, if contemporary science gives us knowledge of the essences of natural kinds it does so by empirical rather than a priori means. W. v. O. Quine argued that appeal to the notion of natural kinds can dissolve two famous paradoxes of confirmation: (i) Carl Hempel’s raven paradox: Intuitively a generalisation like ‘all ravens are black’ is confirmed by observation of its instances, in other words, by the observation of black ravens. Yet this generalisation is logically equivalent to ‘all non-black things are non-ravens’ which is confirmed by observation of, say, a green leaf. But how can observing a green leaf confirm ‘all ravens are black’? (ii) Nelson Goodman’s grue problem: Suppose that observation of the instances of green emeralds confirms the generalisation ‘all emeralds are green’; they are also instances of the generalisation ‘all emeralds are grue’, where ‘grue’ means ‘green before 2030 and blue afterwards’. Why do we take the one generalisation to be confirmed and not the other? It seems that there are some predicates, such as ‘green’, that we are prepared to use to make projections about unobserved objects and others, such as ‘grue’, that are not projectible. We make judgements of similarity in terms of projectible pred- icates. Goodman argued that projectible predicates are those that are entrenched in our epistemic community, and denied that similarity judgements among objects are objective. Quine argued that appeal to natural kinds allows Goodman’s problem to be avoided, because not all predicates are projectible and those that are will be those 306 James Ladyman that are true of all and only the things of a kind. Similarly, the Ravens paradox is avoided if predicates like ‘is non-black’ are ruled out of consideration because they do not refer to natural properties. Clearly the notions of kind and similarity are closely related. The question of whether there are natural kinds is the question of whether there are objective similarities between things, which is the question of whether there are some properties that are natural and in virtue of which similarity and kind membership is definable. But Quine is troubled by this since he thinks that the notion of a kind and the related notion of similarity are of dubious scientific standing. Quine would like to be able to do away with any metaphysical commitments other than to sets of concrete individual things. However, natural properties seem to be intensional while sets are extensional.