Inquiry, Vol. 48, No. 5, 464477, October 2005 Cleansing Science* PAUL M. CHURCHLAND University of California, San Diego, USA (Received 15 April 2005) It is intriguing to be taken on a tour of some highly familiar and much-loved te rritory as seen through the eyes of someone else, someone who brings a different set of convictions and a very different intellectual agenda to the task at hand . The territory, in this instance, embraces the theoretical ambitions and the ex planatory achievements of modern Cognitive Neuroscience. And the alien eyes are the eyes of M.R. Bennett and P.M.S. Hacker, a neuroscientist at Sydney and a phi losopher at Oxford respectively. The authors have a major bone to pick, and not just with contemporary philosophers of mind. More centrally and more importantly , they have a bone to pick with the ways in which contemporary neuroscientists c onceive of their collective undertaking, and with the ways in which those scient ists express their scientific results to one another, and to the scientific comm unity at large. The core complaint is that the discipline of neuroscience is in the thrall of an extended family of conceptual confusions, confusions that infec t and infirm the ambitions of neuroscientists going in, and that infect and infi rm what purport to be their empirical and theoretical findings coming out. Of th is, more in a moment. It will help first to sketch the positive philosophical po sition embraced by the authors. Not because the defense of that background posit ion is first on the authors dialectical agenda their primary aim is plainly criti cal but because we shall understand their critique better if we appreciate the b ackground convictions that motivate it. *Philosophical Foundations of Neuroscience, M.R. Bennett and P.M.S. Hacker. Oxfo rd: Blackwell Publishing Ltd., 2003, 461 pp., ISBN: 1-40-510855-X, $78.95, 70.00, pb., 21.99, $39.95. Correspondence Address: Paul M. Churchland, Department of Ph ilosophy, 0119, The University of California, San Diego, 9500 Gilman Drive, La J olla, CA 92093-0119, USA. Email: pchurchland@ucsd.edu 0020-174X Print/1502-3923 Online/05/05046414 # 2005 Taylor & Francis DOI: 10.1080/00201740500242001

Cleansing Science 465 Bennett and Hacker (hereafter, B&H) view the contemporary intellectual scene pri marily through the eyes of the later Wittgenstein, and through the lens of the t radition of Ordinary Language Philosophy that Wittgenstein helped to found. This perspective underpins the authors conviction that the familiar range of ordinary psychological predicates of perception, cognition, emotion, deliberation, and a ction properly apply to entire persons (in the case of humans) and to entire cre atures (in the case of nonhuman animals), as opposed to any of their parts or bi ological subsystems. It also underpins the authors trenchant conviction that such predicates are properly assigned to persons on the basis of logically adequate cr iteria concerning their publicly observable behavior as it unfolds in their public ly observable physical and social environments. To learn what those criteria are , and how to apply them, is to acquire our ordinary conception of what a cogniti ve creature is in the first place. It is to acquire the literal, non-metaphorica l, and standard use of our familiar folkpsychological vocabulary. As those of us who learned our philosophy in the zeitgeist of the 50s and 60s will recall, the expression logically adequate conveyed the conviction that such criteria inherited their predicate-justifying power not from any empirical considerations, however diffuse or systematic, but from the web of meaning-relations that were said to u nite the specific criterial features at issue with the specific psychological pr edicate for which they were said to be criterial. The authors use of that (proble matic) expression is unchanged from that period, as is the theory of meaning tha t lies behind it. Specifically, any word has its meaning fixed by the rules for its proper use, rules that collectively specify the logically adequate criteria appr opriate for that words application.1 A vital consequence of this view is that to utter a sentence in which one or more of the relevant rules is violated is not to ha ve uttered a falsehood; it is to have uttered something that is strictly meaning less. It is to have expressed, at most, a conceptual confusion. Alas, and as you may have guessed, this is the fate that has befallen much of the conventional w isdom and most of the leading hypotheses accepted by modern neuroscientists. Or so B&H are determined to argue. The book begins with a brief history of neurosci entific theorizing. Aristotle emerges as one of the authors early heroes, largely because of his doctrine that the animative, perceptive, and rational souls are each complex abstract behavioral forms displayed by creatures rather than distinct p articulars or parts somehow possessed by them. And one Nemesius of Emesa emerges as an early villain, mainly for locating various sorts of mental activities in various parts of the brains fluid-filled ventricles, on the empirical grounds tha t damage to distinct areas surrounding the ventricles produced signature kinds o f sensory, intellectual, or motor deficits in the afflicted creature. Nemesius pr esumptive evidence here notwithstanding, the authors comment disapprovingly: the t endency to explain how a

466 P.M. Churchland living being perceives, thinks, feels emotions, etc., by reference to a subordin ate part of that being runs like a canker through the history of neuroscience to this very day. 2 This alleged mereological fallacy consists in ascribing to a part of a creature attributes which logically can be ascribed only to the creature as a whole.3 Historys most notable felon on this score, aver B&H, is a modern figure Rene Descartes whose mind-body dualism located all of ones cognitive states and a ctivities within a non-physical soul, a non-spatial particular distinct from ones behaving physical person. There is indeed a recurring explanatory fallacy in th is neighborhood the fallacy of the homunculus (a supposed smaller person inside the person whose capacities need to be explained) but it is not clear that Desca rtes actually commits this fallacy (he warns against it in his Optics4), nor tha t any substance dualist must. And the authors display a relevant confusion of th eir own. Descartes was, of course, wrong to identify the pineal gland as the locus of the sensus communis, and wrong to think that an image corresponding to the r etinal image (and hence to what is seen) is reconstituted in the brain.5 On the pi neal gland, well said; but the second claim is widely known to be false. Fig. 1b portrays the activity levels of the neurons in the primary visual cortex (V1) o f a monkey, during prolonged visual exposure to the external bulls-eye pattern s hown in 1a.6 Rather like the pixels on a TV screen, the neurons on the cortical surface register a (metrically-deformed) image of the external stimulus by their differential activity. No one thinks that there is any inner homunculus that take s a look at this cortical image, but the relevant neurons all project their activi ty levels, via axonal projections that continue to preserve topological relation ships, to further populations of cortical neurons (such as V2, V4, MT, etc.). So those downstream populations are in a good position to exploit, in their variou s ways, the spatial information evidently contained in V1s cortical image of the original external stimulus. Thus, images do not need to be literally seen for th e spatial information they contain to be causally effective in steering the beha vior of the entire organism whose brain contains them. But they are images nonet heless, for all their being unseen. This is not an isolated example, for the bra in teems with topographic maps of auditory space, somatosensory space, proprioce ptive space, motor space, and so forth. But never mind. For better or worse, B&Hs central criticism of Descartes lies in the charge that he commits a mereologica l fallacy, the fallacy of ascribing to a (presumed) part of a person features th at can only properly be ascribed to the person as a whole. That conceptual confu sion is especially evident, they aver, because the avowedly non-spatial and imma terial mind is not even the sort of thing that could possibly display the comple x behaviorsin-context that are criterial for the proper ascription of perceptual , cognitive, and emotional states. Only something with spatial and physical feat ures could hope to do that. Their main objection to Cartesian dualism,

Cleansing Science 467 Figure 1. accordingly, finds no empirical failing in it. Their objection is purely philoso phical, purely conceptual. Many, this reviewer included, will join B&H in rejecting substance dualism, but the charge that Descartes position is literally senseless out of the starting-gate carries a price. The position cannot, on that account, enjoy any empirical confirmation, no doubt. But for the same reason, it cannot s tand in conflict with any empirical facts either. And yet, it does. Most famousl y, the dualist assumption that the nonphysical mind can exert subtle causal effe cts, on the physical body in general and on the physical brain in particular, vi olates the law of the Conservation of Momentum. That law requires that any chang e in the motion of any physical particle, no matter how tiny, be the result of s ome compensatory (i.e., equal and opposite) change in the (perhaps collective) m otion of some other physical particle(s). In short, the empirical evidence indic ates that the behavior of the physical

468 P.M. Churchland world, including the brain, is closed under the laws of classical mechanics. The re is no dynamical room available for the soul to work its magic. (These manifes tly empirical considerations are precisely what moved the epiphenomenalists, suc h as T.H. Huxley, to abandon substance dualism and to demote mental phenomena to causally impotent nonphysical by-products of brain activity.) Accordingly, subs tance dualism would appear to be entirely meaningful, but false, rather than sen seless to begin with. Who cares, one might ask, so long as the position is put firmly behind us? But B&H have to care, because their analytical critique of the pretensi ons of Cartesian dualism (i.e., its pretensions to be cognitively coherent) is j ust a tactical prelude to laying the very same critique at the feet of those neu roscientifically motivated antiCartesian reductionists who would portray our per ceptual, cognitive, and emotional states as being states of the brain. The autho rs Chapter 3 is entitled, The Mereological Fallacy in Neuroscience, and it presses th e same analytical considerations mutatis mutandis against the contemporary claim that mental states are states of the physical brain. After all, the brain, too, is but a part of the person as a whole. And the brain itself an immobile threepound lump of grayish material forever sealed inside the skull is little or no m ore able to display the complex behaviors-in-context that are said to be criteri al for the proper ascription of perceptual, cognitive, and emotional states than was Descartes immaterial thinking substance. Only the person as a whole can display those behaviors. Ascribing cognitive states to the brain is thus no more meaning ful or conceptually coherent, say the authors, than was ascribing them to an imm aterial soul. This argument may seem a small stone with which to bring down the Goliath of modern neuroscience, but the authors are eager and willing to assume the role of David, sling in hand, and to illustrate their objections in (sometim es mind-numbing) detail. The central two-fifths of the book (pp. 68351) is a seri es of criticisms of the explanatory suggestions and theoretical proposals of ove r two dozen influential figures, including Crick and Edelman from biology; Blake more, Young, Libet, Kandell, Squire, LeDoux, and Zeki from neuroscience; Gregory , Marr, Ullman, Rock, and Johnson-Laird from Psychology; and Damasio and Gazzani ga from Neurology. Philosophers, too, are rebuked for their failings (e.g., Patr icia Churchland and this reviewer, in a late chapter on reductionism; and also D ennett and Searle, in two substantial appendices), but we philosophers are frank ly a side-show in this volume. The authors remain true to their primary aim: lay ing conceptual criticisms at the feet of the several empirical sciences of the b rain. Summarizing those criticisms is impossible, beyond outlining their backgro und rationale, as in the preceding paragraphs. But we may profit from examining some salient examples, to see how the rationale plays out in some focal cases of real importance to everyone. An early complaint

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addresses the common tendency of cognitive theorists to ascribe sundry represent ations to the brain, variously conceived of as maps, or symbols, or images of som se are, at best, misleading metaphors, say B&H. These alleged metaphorical uses ar e so many banana skins in the pathway of their user. He need not step on them an d slip, but he probably will.7 On maps, the authors comment as follows. a map is a pi torial representation, made in accordance with conventions of mapping and rules of projection. Someone who can read an atlas must know and understand these conv entions, and read off, from the maps, the features of what is represented. But t he maps in the brain are not maps, in this sense, at all. The brain is not akin to t he reader of a map, since it cannot be said to know any conventions of represent ations or methods of projection or to read anything off the topographical arrang ement of firing cells in accordance with a set of conventions. For the cells are not arranged in accordance with a set of conventions at all, and the correlatio n between their firing and the features of the perceptual field is not a convent ional one but a causal one.8 And of symbolic descriptions the authors comment as fol lows. For something to be a (semantic) symbol, it must have a rule-governed use. There must be a correct and an incorrect way of using it. It must have a gramma r determining its intelligible combinatorial possibilities with other symbols, w hich is elucidated by explanations that are used and accepted among a community of speakers. There can be no symbols in the brain, the brain cannot use symbols and cannot mean anything by a symbol 9 More generally, Neither in the iconic nor in the lexical sense, could there be any representations of the external world i n the brain The term representation is a weed in the neuroscientific garden, not a t ool and the sooner it is uprooted the better.10 These dismissive remarks are cha racteristic of the text as a whole. Many readers will find such ostentatiously l iteral interpretations, of what are plainly meant to be probing metaphors, to be deliberately deflationary and downright uncooperative. The authors resistance to such metaphors may also appear plain uncomprehending, because the aptness of su ch metaphors is already long established with regard to electronic computers. In deed, the

470 P.M. Churchland desk-top computer on which B&H likely composed their own manuscript is aptly des cribed as following rules (viz., the set of literal sentences that make up the speci fic code or program that the computer is running, MS Word, perhaps), and is also aptly described as deploying a combinatorial grammar upon a lexicon of symbols (viz., the lexicon and the recursive specification of a well-formed formula, that ma ke up the computer language in which MS Word is written). Desk-top computers are artifacts, to be sure, but they were deliberately built to engage in the rule-gov erned manipulation of complex symbols. Such talk now makes perfect sense, at least to computer scientists. Arguably, it is not even metaphorical any longer, given the well-developed theoretical and technological background against which such talk now takes place. Accordingly, given the startling capacities of such machin es, it is a most intriguing empirical hypothesis that the biological brain might be the locus of the same sorts of information-processing activities as are carr ied out in digital computers. One can even see how to test that hypothesis: look in the brain for biological analogs of the structural elements and global organ ization of electronic computers. Certainly, and B&Hs misgivings to the contrary n otwithstanding, such an hypothesis is not meaningless out of the starting-gate. Once again, the hypothesis at issue appears to be entirely meaningful, but false .11 On the matter of locating maps within the brain, the authors complaints are s imilarly uncooperative and even more uncomprehending. The explanatory point of i nvoking neuronally embodied maps, without thereby invoking a homuncular map-read er, is nicely illustrated in the case of the superior colliculus. This smallish subcortical system, common to most mammals, contains three distinct topographic maps of the animals immediate spatial environment: one visual map, one auditory m ap, one tactile (whisker) map, and a final layer of motor neurons underneath the three sensory layers. Those three maps are stacked one on top of the other, and each is metrically deformed so that they are in mutual register. The neurons in the motor map at the bottom of the stack receive axonal projections (orthogonal to the several layers) from the sensory neurons above them, so as to respond se lectively to localized activity in any of those maps. The point of this overall arrangement is to make the animal respond, involuntarily and automatically, to a ny sudden change in its visual, auditory, or whisker sensory inputs, with a visu al saccade that redirects the animals eyes so as to relocate the external stimulu s on the highresolution fovea at the center of the retinal field. (The motor neu rons in the lower map project to the oculomotor muscles.) The superior colliculu s thus functions as an early warning system of potentially interesting changes in th e animals immediate spatial environment, as they may be registered in any one of three distinct sensory modalities. A strong stimulus in any one of

Cleansing Science 471 the three sensory maps is causally sufficient to make the animals eyes aim in the appropriate direction. And a nice feature of this system of distinct but mutual ly aligned maps is that even a very faint or sub-threshold external stimulus, if it registers simultaneously in two or more of the three maps, will be sufficien t to move the eyes in the relevant direction. For such sameplace activations in the distinct sensory maps are simply summed by the motor-neuron dendrites that recei ve stimulation from all three of them. Thus, a faint flicker in your visual peri phery, plus a barely-audible rustle coming from exactly the same direction, can jointly command your explicit visual attention, though neither would have done s o independently.12 This simple example of dynamically interacting maps in the br ain portends a multitude of similar but more sophisticated examples, and it also illustrates the intriguing fact that neuronally-embodied maps are not limited t o representing mundane matters such as local geographical space. For the motor-m ap at the base of the superior colliculus is a map, not of any physical space, b ut of the domain of possible eye-movements: its two orthogonal axes code for dir ection of eye-movement and magnitude of eyemovement, respectively. Here we begin to appreciate that neuronal populations can code for a variety of abstract matt ers as well as concrete ones. Indeed, research on artificial neural networks sug gests that this is typically the result of training a network to simulate some f amiliar cognitive capacity, such as discriminating male from female faces, and r eidentifying the same individual across a diversity of facial photos, as display ed in Cottrells justly celebrated artificial neural network.13 Analysis of the ac tivity-profiles of the face-coding population of 80 neurons at the networks middl e layer revealed that distinct kinds of faces chronically produced signature act ivation vectors in distinct parts of the 80-dimensional activation space, a spac e in which similar faces were coded at highly proximal positions within that 80d imensional map, and very different faces were coded at very distant positions within it. In all, the space of possible activation-codings had been sculpted, by lear ning, into a well-structured map of the domain of possible human faces. Such a m ap is not, to be sure, what you will find in a geographical atlas, or at your lo cal AAA office. It has 80 dimensions rather than two, and the domain mapped is a n abstract domain of possible features rather than a concrete domain of geograph ical places or city streets. But it is still a map in the literal mathematical s ense, for there is a one-to-one projection of the maps internal elements and regi ons onto the abstract features being mapped, a projection in which the similarit y relations between the objective abstract features are systematically reflected in the proximity relations between the maps internal elements. A sensory indexin g of a specific highdimensional point within such a stable background map consti tutes any creatures perception that this abstract feature, among the possible fea tures

472 P.M. Churchland of which it has acquired any conception, is the feature that is currently instan ced in its perceptual field. And that here-and-now information (a selection from a range of antecedent possibilities) can have useful effects on downstream popu lations of neurons, neurons whose learned activationprofiles can produce behavio rs appropriate to the objective features thus perceived. I cannot and will not i nsist that this general approach to animal cognition is correct, though its stru ctural and dynamical virtues have captured many imaginations over the last two d ecades. I sketch it here primarily to illustrate that we are not doomed to empty metaphors and mushy meanings in deploying the notion of a map as part of an acc ount of how cognitive creatures represent and navigate their environments. Such an account may turn out to be false, but it is not crippled by conceptual confus ion from the outset. B&H need to try harder to understand what their neurotheore tic colleagues are trying to say. Even if the neuroscientific uses of terms such as map are neologistic by the standards of the marketplace, they can still make per fect sense by some more informed standards. As science makes conceptual progress (a notion little discussed or acknowledged by B&H), this sort of thing happens all the time. By way of illustration, let me recall to the readers attention the substantial conceptual novelty introduced by Newtons theory of gravity in the lat e Seventeenth Century. And let me explore some possible objections to that theor y, objections in the style of the book here under review. Newtons opening insight , you may recall, was that the Moon is a flung stone, one of astronomical propor tions, a stone constantly falling (towards the Earth) as it pursues its inertial path, doomed never to land because its acquired velocity is too high: its origi nal tangential motion always compensates for its constant Earth-directed acceler ation. Possible objections pour to mind. If the Moon is a flung stone, Mr. Newto n, is there then a sling of suitably astronomical proportions lying somewhere in the Universe, deployed long ago by some astronomical David, perhaps? After all, stones dont move parallel to the Earths surface on their own: stones are essentia lly inanimate bodies. And even if there were some primordial agent equal to the task of flinging the Moon on its trajectory, on what body, pray tell, did that m ighty agent stand in order to perform that cosmic feat? Your use of the relevant terms here is evidently incompatible with some of the presuppositions that make those terms meaningful in the first place. Moreover, and in the same vein, how can something like the Moon, whose distance from the Earth is a constant, cohere ntly be said to be continually falling towards the Earth? Tis a transparent conce ptual

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confusion, for the logical grammar of a falls towards b demands that the distance be tween a and b get swiftly smaller over time. These evident conceptual confusions simply beget further conceptual disasters. For, on your own theory, Mr. Newton, you will have to say that the Earth itself is also a flung stone, constantly falling wards the Sun!! The two conceptual failings noted earlier both reappear in this case also, and to the same incoherent effect. Moreover, at midnight, when the Ea rth is between me and the Sun, the Earth must then be falling away beneath my fe et! Yet again, you are misusing the term falling. To makes things even worse, eviden tly the Sun, too, will be a flung stone, on your view. If it is, towards what body, pray tell, is it falling? And if you have an answer, Mr. Newton, I would repeat the question once more, to your iterated embarrassment. Clearly your conceptual tran sgressions have launched you on a dialectical regress from which there is no esc ape. Enough parody. I suggest that B&Hs complaints about the theoretical proposal s of modern cognitive neuroscience are no more substantial than, and no differen tly motivated from, the conceptual objections laid at Newtons feet in the preceding p aragraphs. Such objections do no more than highlight the independently obvious f act that the new theory violates some of the default expectations of the average ten-year-old. But where is the crime in this? Why should we make those baseline expectations permanently criterial for the meaningful use of the terms at issue ? Were we permanently to cleave to the standards of conceptual hygiene14 thus impose d by B&H, we would be doomed to only the most trivial of scientific advances. Fo r our conceptual imaginations would then be confined to what is currently taken, by the average ten-year-old, to define the bounds of sense. Courageously enough, B& H address some of these very issues. In a chapter entitled Methodological Reflecti ons, they concede that our theories may indeed change over time, and that the mean ing of the concepts within them may well change along with them. All that is req uired, for such legitimate conceptual evolution, is that the scientific theorist s involved be forthright about laying down the new rules for the new use of the (old) theoretical terms involved. This apparently liberal concession motivates n o change in their overall critique, however, for two reasons. First, neuroscient ists have not been forthcoming in the least, complain the authors, about laying down genuinely new rules for the use of the new (theoretical/explanatory) terms that they wish to use. To the contrary, they continue to lean on the antecedent meanings of common terms such as representation, information, perceives, rememb h, but to use them in ways that violate some of the antecedent rules for

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their proper use. Accordingly, while conceptual change of the kind just acknowle dged might be possible here, the worlds cognitive neuroscientists are not yet liv ing up to the demands required to achieve it. Put this way, their complaint star ts to appear within shouting distance of some approximation to the truth of the matter. Cognitive theorists are indeed groping forward in the darkness; metaphor s are indeed the rule rather than the exception; and our theoretical concepts in this domain are still a long way from being settled. And yet, the authors charge of rampant conceptual confusion still seems to me to be wildly overstated. For one thing, groping forward with fluid metaphors is the perfectly normal and heal thy fate of any attempt to make significant new science. It is not pathological in the least, so long as the process is suitably self-critical. And for another, some of the relevant new theory has been made usefully explicit and genuinely n on-metaphorical. Recall our earlier discussion concerning the potential ascripti on, to the brain, of sentence-like representations on the one hand, and map-like representations on the other. In both cases, we noted, an explicit conceptual b ackground is now firmly in place, a background equal to the task of giving coher ent and determinate meaning to the terms of the theoretical vocabulary involved. The background is provided by modern computational theory in the first case, an d by vector algebra in the second. B&H are simply wrong to dismiss both, or eith er, of these competing research paradigms. At least, they are wrong to dismiss t hem on the grounds that they are sheer conceptual confusion. This issue marks a substantive or factual difference of opinion, between this reviewer and the auth ors, on how we read the current state of cognitive neuroscience. It is not a phi losophical disagreement. Philosophical disagreements, however, are not far away. A further reason, according to B&H, why the concepts of folk psychology are poo r candidates for the sorts of conceptual changes regularly found in the sciences is that the concepts of folk psychology are not theoretical concepts to begin w ith. Their meaning is fixed, not by a web of explanatory hypotheses whose truth is, at best, always contingent. Rather, their meaning is fixed by a family of co nceptual truths, truths that reflect conventional stipulations, rules-ofuse, or log adequate criteria. Accordingly, their meanings are simply not subject to the sorts of revisionary pressures to which theoretical concepts are always vulnerable. T his is a philosophical issue familiar to the entire profession: Are there any ne cessary truths, constitutive of meanings, truths that are forever beyond any emp irical or factual refutation? Since Quine, the bulk of the philosophical profess ion has been inclined to say no. But some philosophers, B&H included, continue to sa y yes, and, as the reader will by now appreciate, this conviction underlies almost e verything said in their very large book. And it underpins their conviction that conceptual issues are entirely distinct from empirical issues, and that only phi losophers can

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effectively address the former. The authors discuss the issue, very briefly, in a late footnote, but remark that This is not the place to argue the matter (p. 380). Fair enough. I wont argue the matter here either. Hacker has addressed the issue at some length in an earlier book,15 as has this reviewer.16 The fundamental ph ilosophical disagreement here is best simply acknowledged, to be judged by the r eader as the reader sees fit. There remains, however, a final issue that demands our attention, however briefly. It concerns the possibility that the authors th emselves, despite their declared conceptual caution, have stumbled into the same sort of metaphorical theorizing, and into the same sorts of conceptual confusio ns, that they ascribe in such relentless detail to their neuroscientific colleag ues. This final issue concerns the authors positive theory of how words come to h ave the meanings that they do, a positive theory that leans heavily on the notio n of rules, rules governing the correct use of words a positive theory that lean s equally heavily on the notion that cognitive creatures actually follow such ru les. Certainly the notion of rules, and the notion of creatures diligently follo wing them, has played a prominent explanatory role in both philosophy and the co gnitive sciences. The authors have no shortage of company in leaning on such not ions. But the natural home of such notions lies in social contexts where explici tly articulated rules are stated, remembered, and explicitly applied long after their initial apprehension. Here one can legitimately explain both individual ac ts and chronic patterns by appealing to the rules that have come to guide the ag ents behavior. A driver stops and waits briefly at a busy intersection out of res pect for the rule, At an unregulated intersection, through traffic has the right-o f-way over turning traffic. A poker player folds his hand, guided by the rule, Never draw to an inside straight. A student replaces to boldly go with boldly to go, mot by her teachers rule, Do not split an infinitive. A citizen rushes to beat the closin g of the post office motivated by the law, Tax returns must be postmarked no later than April 15th. All of these, and many more, are literal cases of rule-governed behavior. Awareness of the rule, and respect for it, jointly serve to explain th e relevant behavior. More dubious, however, is the common tendency to explain pe oples general social and moral behavior, for example, in terms of the set of moral rules to which they supposedly adhere. The worries here begin, but do not end, wit h the fact that the intricacy of any normal persons ongoing moral conduct far exc eeds what might be accounted for by any rules that the individual might be able to explicitly articulate. If prompted, people can be made to utter a small handf ul of platitudes (Do unto others ), but the gap between the complexity of their socia l behavior and the poverty of their voiceable rules is enormous. This familiar p oint underlies the current tradition of Virtue Ethics, a tradition that reaches back to Aristotle, a tradition that sees moral knowledge as a complex weave of perce ptual and behavioral skills,

476 P.M. Churchland slowly acquired over long experience with the ebb and flow of social reality. B& H, I surmise, might have some nontrivial sympathy with such a position. If so, h owever, they must see the common tendency to explain peoples ongoing conceptual a nd linguistic behavior, in terms of the rules of use to which they supposedly adhere , as being an even more dubious deployment of this general explanatory strategy than was displayed in the case of moral competency. A normal English speaker has a vocabulary of perhaps 20,000 words, for each of which at least a small handfu l of rules would be necessary to adequately guide its use. If we make a rough gu ess of five rules per word, we are looking at a presumptive total of 100,000 rul es embraced by any normal English speaker. But to borrow a phrase from B&H this must be confused. For none of us could even begin to articulate any such mammoth list of rules. Nor it is plausible that our ongoing speech is literally governe d by the repeated (on a millisecond time-scale) application of such rules. We ne ed some other account of how human speech and human thought is produced. Indeed, the vast size of the required rule-corpus and the problem of deploying its elem ents relevantly in real time (recall that the biological brain is roughly a mill ion times slower than an electronic computer) merely introduce the difficulties facing such an account. A still more fundamental problem is that, in order to co mprehend and deploy the rules that supposedly give our concepts meaning, we woul d already have to possess concepts adequate to recognizing the circumstances app ropriate for the application of those rules, and we would have to possess concep ts adequate to understand what those rules mean in the first place. Accordingly, B&Hs preferred account of how meaning arises for cognitive creatures appears its elf to be a presumptively homuncular account, requiring an inner creature with a ntecedently meaningful concepts in order to explain a creatures supposed command of the rules that give meaning to its concepts. The irony here is not just that B&H appear to be guilty of illegitimately redeploying cognitive concepts outside of the contexts proper for their nonmetaphorical use, nor that such a redeploym ent smacks additionally of explanatory homuncularism (though all of this would b e irony enough). The real irony is that their peculiar critique of modern cognit ive neuroscience depends essentially on their peculiar rules-based theory of mea ning, a semantic theory that is itself an instance of exactly the type of theory that, according to B&H, needs to be dismissed. (I detect a failure of conceptua l hygiene very close at hand.) Physician, physician, heal us all if you can. But f irst, and before this, dear physician, heal thyself. I close by remarking that the re is much of interest in this large book that has gone unaddressed in this brie f review. To take two of many examples, the authors mount an extended critique o f Damasios intriguing account of human and animal emotions as the activities of a n evolutionarily primitive sensorimotor system, a system whose function was and stil l is to monitor and modulate the creatures internal visceral milieu, as opposed t o its

Cleansing Science 477 external environment. They also spend a good deal of time attempting to rebut th e now-familiar view that the assembled concepts of commonsense folk psychology c onstitute a sophisticated predictive/explanatory theory of the inner grounds of daily human behavior. I am favorably inclined towards both accounts, but I have resisted the impulse to rise to their defense. The authors of this book have a h ighly general agenda to press, based on a positive philosophical position, an ag enda that reaches far beyond these comparatively local matters. My first duty wa s to make clearly available to the reader what to expect from their mammoth unde rtaking. With the reader now duly advised on the big picture, these local matter s can be left to take care of themselves. Notes 1. To be sure, this use of the adverb logically is notably at odds with what has bec ome the standard meaning of the term, one that deliberately abstracts from seman tic matters. Thus, logically true now implies true for purely formal or syntactic reas ons. But never mind. For reasons that will emerge, I wish to set an immediate exam ple of tolerance where divergence from semantic norms is concerned. p. 22. p. 29 . Translated by J. Cottingham, R. Stoothoff, and D. Murdoch, The Philosophical W ritings of Descartes, vol. 1. (Cambridge: Cambridge University Press, 1985), p. 167. Op cit., p. 29. Tootell, R.B., et al (1982) Deoxyglucose analysis of retinoto pic organization in primate striate cortex, Science, 218, pp. 902904. The neurons t hat were preferentially active during visual stimulation took up more of the blo ods radiation-tagged glucose than did the inactive neurons. This allowed the anim als cortical surface to be subsequently developed, as if it were a piece of photograp hic film, to finally produce the genuinely visible image in 1b. p. 80. p. 80. p. 146. p. 143. I say false because, as it happens, research into the microanatomy and the physiology of the brain reveals an internal structure and a mode of activit y quite different from that found in a serial-processing, program-running, digit al-coding electronic computer. But B&H can draw no comfort from that. Meaningles s hypotheses cannot be shown to be false. By the way, this is not an alien syste m. Humans have one too. When your attention wanders away from the red traffic-li ght which has stopped you, and you then flick your gaze back to find it already turned green, it is your superior colliculus that detects the light-change and t hen reflexively redirects your eyes. For a pictorial summary of this accessible example, see Churchland, P.M., The Engine of Reason, The Seat of the Soul (Cambr idge: The MIT Press, 1995), pp. 3853. The expression, so help me, is theirs. This first invitation to cleanliness occurs on p. 116. It is repeated at the foot of p. 381. P.M.S. Hacker, Wittgensteins Place in Twentieth-Century Analytic Philoso phy (Oxford: Blackwell, 1996), ch. 7. P.M. Churchland, Scientific Realism and th e Plasticity of Mind (Cambridge: Cambridge University Press, 1979), ch. 3. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.