The Multiple Realization Book OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi The Multiple Realization Book Thomas W. Polger & Lawrence A. Shapiro 1 OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi 3 Great Clarendon Street, Oxford, OX2 6DP, United Kingdom Oxford University Press is a department of the University of Oxford. It furthers the University ’ s objective of excellence in research, scholarship, and education by publishing worldwide. Oxford is a registered trade mark of Oxford University Press in the UK and in certain other countries © the several contributors 2016 The moral rights of the authors have been asserted First Edition published in 2016 Impression: 1 All rights reserved. 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OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi To our children, multiple but each uniquely realized, even the triplets OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi Contents Preface ix Acknowledgments xi List of Figures and Tables xiii Part I. Whence Multiple Realization? 1. Physicalism and Multiple Realization 3 2. Realization and Multiple Realization 18 3. What Is Multiple Realization? 37 4. Multiple Realization and Relevant Differences 60 Part II. The Evidence for Multiple Realizability 5. Evidence for Multiple Realization: Neural Plasticity 83 6. Evidence for Multiple Realization: Kind Splitting and Comparative Evidence 99 7. The Likelihood of Multiple Realizability 123 8. The Computationalist Argument for Multiple Realizability 150 Part III. After Multiple Realization 9. Putnam ’ s Revenge 175 10. Mental Causation and the Autonomy of Psychology 194 Guide for Teaching and Learning 221 References 229 Index 249 OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi Preface It is often said that René Descartes set the agenda for philosophy of mind and psychology in the seventeenth century. Classes and textbooks begin with Descartes ’ arguments for dualism of mind and body — the view that minds and bodies are distinct and incompatible kinds of substance, res cogitans and res extensa . Most philosophers now regard Descartes ’ argu- ments to be defective, and even some of his contemporaries saw clearly the main problems that his dualism faced. Nevertheless his construction of the problem of understanding the mind remains in fl uential. Doing better than Descartes ’ dualism is a benchmark for philosophical theories of the mind. And, for many philosophers of mind, the fear that one ’ s view collapses into dualism — or even resembles it — remains a serious one. It is time to move beyond this archaic framework. As Jaegwon Kim correctly notes, since the mid-twentieth century “ the mind-body problem — our mind-body problem — has been that of fi nding a place for the mind in a world that is fundamentally physical ” (1998: 2). But rejecting Cartesian dualism is one thing; fi nding a compelling alternative quite another. The correct response must do more than simply narrow serious proposals about the nature of mind to those that admit only physicalist monism. The lesson of dualism ’ s failure is not just that Descartes was wrong that minds are res cogitans . Rather, the lesson is that the study of the mind must proceed with the same conceptual tools and resources that philosophers and scientists have applied in all other natural domains. The right response is not simply to restrict the possible space of answers, but to reframe the question. We take as a starting point that a science of the mind should begin — and will someday end — in the same world of mountains, seas, animals, and atoms that other sciences investigate. As Kim emphasizes, we must pursue “ mind in a physical world. ” In doing so, we fi nally abandon the old mind-body problem once and for all and replace it with the more familiar, but of course still dif fi cult, problem of developing the broadly empirical study of minds. Some philosophers worry that adopting an empirical approach to the nature of minds threatens the signi fi cance of their contributions. Just as a kind word and a couple of dollars will get you a cup of coffee, so too a OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi philosopher and a neuroscientist will crack the puzzle of mentation. But if the worry is that philosophers will not always have the last word about the properties of minds, then we see no great loss. On the other hand, if we understand philosophy as trying, as Wilfrid Sellars suggests, “ to understand how things in the broadest possible sense of the term hang together in the broadest possible sense of the term ” (1963: 1), then philosophers need not worry that there is a choice to be made between scienti fi c and philosophical theorizing. That is another anachronistic dualism that we do well to leave behind. Understanding what it means for minds to be physical, and the implications of this claim for the sciences of the mind, leaves plenty to do for philosophers, even granting the need of empirical methods for a complete picture of mental phenomena. OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi x PREFACE Acknowledgments We would like to thank audiences in Madison, Shreveport, Cincinnati, Birmingham, Dover, Berlin, Lausanne, Paris, Jerusalem, Cologne, Leuven, Kazimierz Dolny, Seoul, Evanston, the Philosophy of Science Association, the Society for the Metaphysics of Science, the Southern Society for Philosophy and Psychology, and the International Society for the History, Philosophy, and Social Studies of Biology. Our view of multiple realization developed incrementally at a series of workshops over the past decade, whose attendees included: Fred Adams, Ken Aizawa, John Bickle, Dan Brooks, Cédric Brun, Carl Craver, Zoe Drayson, Markus Eronen, Carrie Figdor, Jörg Fingerhut, Gary Fuller, Carl Gillett, Jens Harbecke, Vera Hoffman-Kloss, Tobias Huber, Philippe Huneman, Marie Kaiser, Jesper Kallestrup, Lena Kästner, Beate Krickel, Corey Maley, Alex Manafu, Mohan Matthen, Karen Neander, Marieke Rhode, Bob Richardson, Rob Rupert, Christian Sachse, Raphael Scholl, Elliott Sober, Patrice Soom, Jackie Sullivan, Kari Theurer, Sven Walter, and Markus Wild. We have also bene fi ted from feedback from research groups based in Cologne and Jerusalem that include some of the above people as well as Eli Dresner, Meir Hemmo, Arnon Levy, Oron Shagrir, and Orly Shenker. We are especially grateful to our friends and colleagues who discussed portions of this manuscript with us: Ken Aizawa, Rosa Cao, Tony Chemero, Valerie Hardcastle, Doug Keaton, Brian Keeley, Colin Klein, Gualtiero Piccinini, Angela Potochnik, Bob Richardson, Christian Sachse, Rob Skipper, and Elliott Sober. We are also indebted to Peter Momtchiloff, Eleanor Collins, Sarah Parker, Dawn Preston, and two anonymous readers for Oxford University Press for shepherding this project. Tom Polger ’ s work on this project was made possible in large part by support from the Charles P. Taft Fund and Taft Research Center at the University of Cincinnati, and by a sabbatical leave from the University of Cincinnati. Larry Shapiro is grateful to the University of Wisconsin for a sabbatical leave during 2014 – 15. OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi List of Figures and Tables Figure 1.1 Fodor ’ s picture of the special sciences. From J. Fodor (1974). With permission of Springer. 10 Figure 3.1 Cephalopod (left) and vertebrate (right) eyes. From Harris 1997: 2099. Copyright (1997) National Academy of Sciences, U.S.A. 45 Figure 4.1 Mechanical watch movement. Artwork by permission of the Elgin Area Historical Society. 70 Figure 4.2 Kinds of eyes (Land and Fernald 1992). Modi fi ed with permission from the Annual Review of Neuroscience , Volume 15, ©1992 by Annual Reviews, <http://www.annualreviews.org>. 75 Figure 5.1 (A) Area 3B of the somatosensory cortex devoted to representation of the hand. (B) The ventral portion of the hand represented in area 3B. (C) The somatosensory representation of the ventral portion of the hand. (D) The effect that severing the median nerve has on the representation of the hand. (E) The somatosensory cortex after about one month of recovery. Areas D1, D2, and D3 are now innervated by inputs from the dorsal surface of the hand via the radial nerve. D1 – D3 now represent dorsal portions of the fi rst three digits and pads of the monkey ’ s hand. (F) Normal cortical map recovered (Kaas 1991: 143). Modi fi ed with permission from the Annual Review of Neuroscience , Volume 14, ©1991 by Annual Reviews, <http://www.annualreviews.org>. 91 Figure 6.1 “ A tentative taxonomy of long-term memory and associated brain structures ” (Thompson and Kim 1996: 13439). Note that this fi gure does not include short- term memory systems; and further distinctions have been introduced since its time of publication. Reproduced with permission of American Association for the Advancement of Science. 101 Figure 6.2 Patient evaluations of pain sensations. Melzack and Torgerson 1971. Used by permission. 112 OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi Figure 6.3 Left: Human auditory cortex circuits compared to avian DVR. Right: Macroanatomy showing locations of homologous neurons. Reprinted from Karten 2013, with permission from Elsevier. 116 Figure 6.4 “ Comparison of anatomical instantiations of Heiligenberg ’ s jamming avoidance response algorithm in three genera of weakly electric fi sh ” (reprinted from Keeley 2000: 456). Copyright 2000 University of Chicago Press, used by permission. 118 Figure 6.5 Time comparison circuits two wave type electric fi sh species (B and C) that produce the JAR response. The top species (A) is a pulse type that does not implement the JAR algorithm but instead avoids interference by making use of endogenously available signals caused by its own electrical discharges — electric organ corollary discharges (EOCD). Artwork reprinted from fi gure 5 of Kawasaki 2009. Used by permission of the Zoological Society of Japan. 119 Figure 10.1 A Rube Goldberg machine: The Self-operating napkin. Artwork Copyright © and ™ Rube Goldberg Inc. All Rights Reserved. RUBE GOLDBERG ® is a registered trademark of Rube Goldberg Inc. All materials used with permission. <http://www. rubegoldberg.com>. 208 Figure 10.2 Our illustration of the relations between different explanatory theories or models emphasizes the importance of identifying some entities across different sciences, explanations, or models (e.g., A, B, C). But our picture does not assume that identi fi cation is always possible, and dispenses with the assumption that different explanations and models can be neatly ordered into layers or hierarchies. 218 Table 1.1 Scorekeeping theories in the philosophy of psychology 17 Table 9.1 Scorekeeping theories in the philosophy of psychology, revised 176 Table 9.2 Scorekeeping theories in the philosophy of psychology, second thoughts 178 Table 10.1 Scorekeeping theories in the philosophy of psychology, revisited 211 OUP CORRECTED PROOF – FINAL, 2/6/2016, SPi xiv LIST OF FIGURES AND TABLES P A R T I Whence Multiple Realization? OUP CORRECTED PROOF – FINAL, 27/5/2016, SPi OUP CORRECTED PROOF – FINAL, 27/5/2016, SPi 1 Physicalism and Multiple Realization 1. Post-Cartesian Physicalism 2. Functionalism and Explanation in Psychology 3. What Good Is Multiple Realization? 1 Post-Cartesian Physicalism Once we stop worrying about Descartes ’ mind-body problem and start worrying about the place of the mind in a physical world, we must set about evaluating theories about minds in the same ways that we evaluate broadly scienti fi c theories of anything else. In short, we must view philosophy of mind as a species of philosophy of science. And theory selection in the philosophy of mind will be like theory selection in any other broadly scienti fi c inquiry. The pioneering twentieth-century physicalists who theorized about the mind defended their views precisely within the context of such broadly empirical considerations. Criteria for theory selection that have been especially salient for philosophy of mind-as-science include empirical adequacy, simplicity, relevance, and generality. Herbert Feigl, U. T. Place, and J. J. C. Smart articulated and defended a mind-body identity theory — the view, as Smart put it, that “ sensations are brain processes ” (1959: 144, 1961). Already by the mid-1900s, all three believed that the empirical evidence justi fi ed the belief that a brain-based theory of psychology would be empirically adequate. And, although they differed on precisely how to apply the criterion of simplicity — a vexed notion in its own right — they each held that the mind-brain identity theory is simpler than the alternatives. In particular, they argued OUP CORRECTED PROOF – FINAL, 27/5/2016, SPi that the identity theory is simpler than dualism, which at that time remained among the main competitors. But it is important to note that the early identity theorists didn ’ t argue that the identity theory is simpler than dualism merely because the identity theory postulates only one kind of stuff — the physical stuff — whereas dualism postulates two. That application of simplicity would cut no ice if the dualist theory put the extra mind-stuff to good work. Rather, in light of the dif fi culty of understanding how mind-stuff could causally interact with physical stuff, the early identity theorists concluded than any version of dualism would have to endorse epiphenomenalism . The dualist, that is, would be forced to concede the causal impotence of mind-stuff. Mind as distinct from matter would make no difference in the world. So the complaint against dualism is not just that it postulates two kinds of stuff, but that it postulates a kind of stuff that plays no role in explaining the capacities of creatures who have minds. A main pur- pose of theorizing about minds, after all, is to construct an explanation of the behaviors, thoughts, feelings, and so forth of creatures such as us. Epiphenomenalist theories are less simple because they postulate entities that don ’ t appear to contribute to that explanatory project. In applying the theoretical criterion of simplicity in this way, the early identity theorists were not just counting substances but endorsing more substantive desiderata: Psychological states, whatever they are, should have some causal effects. In addition to simplicity, some of the identity theorists also emphasized another theoretical virtue that they saw as speaking in favor of their own view and against Cartesian dualism. Smart asserts “ That everything should be explicable in terms of physics . . . except the occurrence of sensations seems to me to be frankly unbelievable ” (1959: 142). Here Smart expresses a kind of conservatism. Every successful scienti fi c endeavor — physics, geology, chemistry, biology — adopts a purely physicalist perspective, at least in the sense that the domains they investigate are assumed to consist, ultimately, of physical matter. One should expect for this reason that the study of minds would conserve this trend. Certainly, in any case, one should pursue a science of the mind with the assumption that its main commitments will be consistent with those of other sciences rather, as the Cartesian dualist maintains, wholly distinct. Another mid-twentieth-century approach to the mind responded to the perceived consequences of dualism differently. Behaviorists argued WHENCE MULTIPLE REALIZATION ? OUP CORRECTED PROOF – FINAL, 27/5/2016, SPi that postulating “ internal ” psychological states — whether states of brains or of mind-stuff — is not necessary for understanding the oper- ations of the mind. Psychology ought simply to be, as John Watson put it, “ the science of behavior ” (1913). Internal psychological states are as irrelevant for explaining behavior as immaterial thinking substances would be. B. F. Skinner, for example, argued adamantly that internalist explanations of psychology, whether mentalistic or neurological, adopt indefensible and unnecessary theoretical posits (1953). From here, it is a short leap to the idea that internal psychological states do not exist at all. Some behaviorists thought that the body is just a behavior machine, as might be true of organisms like wasps and whelks (cf. Dennett 1984 and Keijzer 2013). Psychological states, if mentioned at all, are treated as states of the total organism, rather than internal causes or working parts. By the late 1960s it seemed clear that behaviorism, at least in its sparest forms, could not meet the minimum standard of empirical adequacy. Chomsky argued that its predictions did not match the data, or that the behaviorist program rested on a vicious sort of post-hoc reasoning (1959); and his criticisms convinced many philosophers and cognitive scientists. 1 But even before Chomsky, behaviorism ’ s opponents noted that the use of simplicity to argue against all “ internal ” theories of the mind is problematic. Simplicity is only one criterion among many, and one that is decisive (if at all) only when all other factors are equal. The behaviorist does not have a clear case for simplicity, but at best a case of competing theoretical values. Nonetheless, despite behaviorism ’ s failures, we might still fi nd reason to praise its commitment to the same kind of conservatism we see Smart embracing. As the identity theorists before them, behaviorists resisted the desire to characterize mental phenomena as sui generis and inexplic- ably apart from the rest of the natural world that scientists hope to describe and understand. If in the end they denied the existence of the very phenomena that we might suppose should be the target of psycho- logical investigation, they did so not because these phenomena were beyond the reach of a physically oriented psychology, but because, so they believed, such a psychology could proceed without them. 1 Chomsky ’ s in fl uence is generally recognized even by those who are critical of his arguments, e.g. MacQuorcodale (1970) and Palmer (2006). PHYSICALISM AND MULTIPLE REALIZATION OUP CORRECTED PROOF – FINAL, 27/5/2016, SPi