Ramsey Sentence Realism as an Answer to the Pessimistic Meta-Induction Mark Newman†‡ John Worrall recently provided an account of epistemic structural realism, which ex- plains the success of science by arguing for the correct mathematical structure of our theories. He accounts for the historical failures of science by pointing to bloated on- tological interpretations of theoretical terms. In this paper I argue that Worrall’s ac- count suffers from five serious problems. I also show that Pierre Cruse and David Papineau have developed a rival structural realism that solves all of the problems faced by Worrall. This Ramsey sentence realism is a significant advance in the debate, but still ultimately fails for its incomplete account of reference 1. Introduction. The No Miracles Argument for scientific realism states that scientific realism is the only philosophy of science that doesn’t make the success of science a miracle. Without adopting realism concerning the entities, processes and theoretical laws of mature and successful contem- porary scientific theories, we are left with no explanation for scientific accomplishments (such as our remarkable ability to predict the outcome of certain quantum phenomena to ten decimal places). We should there- fore accept scientific realism. On the other hand, the pessimistic meta- induction reminds us that the history of science shows that most of what we previously considered to be mature, successful scientific theories were to a greater or lesser extent, false. The historical evidence should lead us to conclude that our inference methods in the sciences are not reliable, and hence we should also conclude that our current theories are most likely false; scientific realism should be rejected. Philosophers who advocate either one of these arguments are hard †To contact the author, please write to: Department of Philosophy, University of Minnesota, Duluth, 1121 University Drive, Duluth, MN 55812-3027; e-mail: [email protected]. ‡Many thanks to Craig Callender for his critical comments on this paper, as well as many hours of extremely helpful discussion on this topic in general. I would also like to thank Stathis Psillos. Philosophy of Science, 72 (December 2005) pp. 1373–1384. 0031-8248/2005/7205-0059$10.00 Copyright 2005 by the Philosophy of Science Association. All rights reserved. 1373 1374 MARK NEWMAN pressed to explain away the cogency of the opposing view. Those who advocate a full blooded scientific realism are stymied by examples from the history of science of very successful, yet false theories. Examples in- clude the caloric theory of heat, phlogiston theory, and theories of the luminiferous ether. Antirealists are hard pressed to give an explanation for the tremendous success of theories which are, they believe, false. Progress has been made. Realists have recognized the need for a more sophisticated view that doesn’t argue for the truth of whole theories, but rather sees their success as due to their being only mostly correct. Theories are permitted a degree of inaccuracy in descriptions of theoretical entities, while still ultimately qualifying as approximately true. Antirealists object that such notions are vague and unsatisfactory. They argue that using a rule that infers from the success to the truth of our best theories is ille- gitimate. Not only does success fail to license claims to correct reference of theoretical entities, which is a necessary condition for the truth of a theory, but also approximate truth is a hopelessly vague concept that encourages realists to generate ad hoc historical accounts of anomalous cases like phlogiston or the ether. In response to such accusations realists have further refined their ac- counts of what it is that we are justified as claiming to be true in our scientific theories. Some have moved to entity realism, and argue that we can infer from empirical success to the existence of the entities of a theory, just not to all of the theoretical claims attached to those entities. Some have adopted what I shall call ‘essential’ realism, arguing that a theory’s success is due to its correctly referring to just those elements (entities, processes, etc.) that were essential to the derivation of its predictions. Others have adopted a structural realism, where what is right in scientific claims is just the structure of those theories. It is this last view that concerns us here. 2. Structural Realism. Structural realism comes in at least two forms: epistemic and ontic. In what follows I shall focus only on the former (the latter is far more contentious, and as yet overly restrictive). John Worrall recently provided an account of epistemic structural re- alism (Worrall 1989). On his view, the history of science does indeed show dramatic discontinuities at the theoretical level, and hence we are justified in our skeptical attitude toward theoretical entities posited by past and current science. However, these interpretive blunders are offset by re- markable continuities in mathematical structure, the equations of our theories. It is in virtue of such mathematical continuity, which goes beyond the merely empirical level, that our optimistic No Miracles Argument is justified. Since our scientific theories seem to exhibit significant continuity RAMSEY SENTENCE REALISM 1375 not just empirically, but also structurally, we should not be surprised that science has in general been a very successful endeavor. Structural realism not only points out the structural continuity apparent in theoretical transitions, it also provides an explanation of these conti- nuities. The claim is that structural realism provides an epistemic con- straint on what it is possible for us to know about the world. This idea obviously relies upon a clear distinction between the structure and content of our theories. It is this distinction that separates out those parts of a theory which we are justified in believing as true from those that are mere conjecture. Worrall views the dichotomy as that between a theory’s math- ematical equations and the theoretical interpretation of its ontology. Where there exists mathematical continuity across theory transitions and revolutions, we are justified in believing we have accurately hooked onto the world. His claim is that it would be an error to believe in theoretically interpreted ontology because it is just this kind of thing we find suffering radical discontinuity across theory transitions. Thus, structural realism adopts a realist position to the degree that it believes in structure, which is beyond the empirical. It rejects traditional realism by drawing an ep- istemic line at structure and discarding all theoretical interpretation. On the other hand, structural realism avoids instrumentalism because it views the mathematical structure in our theories to be a true representation of relations between unobservable entities, not merely a calculational device for generating predictions. Worrall’s aim is to overcome the pessimistic induction with an account of successful science that marks out what is true, and at the same time explains radical theoretical discontinuity. To illustrate what he means he uses as an example the transition from Fresnel’s to Maxwell’s theory of light. The structural realist claims that Fresnel’s theory made correct predic- tions because it accurately identified certain relations between optical phe- nomena, and especially because these phenomena depend upon something or other undergoing periodic change at right angles to the light—even though he was utterly wrong about the theoretical mechanisms involved. The point Worrall wants to emphasize is that Fresnel’s theory didn’t just accidentally make some correct predictions, it made them because it had accurately identified certain relations between optical phenomena. However, one might ask, is this example idiosyncratic? Will structural realism be able to account for other revolutionary changes in science? Well, no not exactly. This case is peculiar in that the equations were transmitted entirely in tact. Worrall thinks that in other cases the equations will be limiting cases of the new equations, and hence, strictly speaking inconsistent. To defend this idea he appeals to what he calls the ‘Corre- spondence Principle’: mathematical equations of the old theory are limiting 1376 MARK NEWMAN cases of those in the new. This principle actually acts as a heuristic in developing new theories. It is applicable purely to mathematics, and not to the theoretical terms that might be used when interpreting the math- ematics. It is a rule that seems to be at play in the history of physics, and is one that legitimizes structural realism over traditional realism. Worrall also rejects the requirement that entire theories make the world comprehensible, claiming that it is a mistake to think we can ever ‘un- derstand’ the nature of the basic furniture of the universe. The structural realist embraces instances where a theory is so successful that we are required to adopt a problematic concept (like action at a distance) as a primitive part of our ontology. Our desire to explain is merely a symptom of our antecedent metaphysical prejudices. Structural realism therefore rejects the metaphysics of theoretical interpretation while embracing a formal realism. 3. Problems with Worrall’s Account. The account given by Worrall is an advance over traditional realism in some respects, but suffers from at least five serious problems. First, there is ambiguity in Worrall’s use of the term ‘structure’. If we take ‘structure’