Pains, Brain States and Scientific Identities

Mind Association

Pains, Brain States and Scientific IdentitiesAuthor(s): Stephen WilliamsSource: Mind, New Series, Vol. 87, No. 345 (Jan., 1978), pp. 77-92Published by: Oxford University Press on behalf of the Mind AssociationStable URL: http://www.jstor.org/stable/2253362 .

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Pains, Brain States and Scientific Identities

STEPHEN WILLIAMS

I

In this paper I argue in favour of type identities between sensations and neural states, starting from the manifest parallelism of sensations and physical events, and adopting a view of sensations as non-intentional episodes. By almost symmetrical contrast, Davidson's well-known argument for token identities patently excludes sensations from its scope, defines mental events by their intentionality, and depends on their non-parallelism with the physical realm (Anomalism of the Mental) to secure its conclusions.1 A common consideration, central to both arguments, is the fact of causal interaction between the mental and the physical-a fact which, I suggest, provides the strongest single force in the materialist direction. However, unlike Davidson, my arguments are not a priori.

II

Assuming, then, that type identities of sensations and brain states are not conceptually impossible (violate no category difference), I maintain that there are powerful grounds which tell in favour of an identity theory and against dualist interactionism and epiphenomenalism. These are grounds of superior explanatory power.

An initial indication of these grounds seems to me so intuitive as to require little elaborate defence. Any true causal statement implies the applicability of some strict covering laws which are universal and as such support counterfactual conditionals. Now at an ordinary empirical level of experiment or practical knowledge (where the concept has its roots) such laws, if known or envisaged, will of course be considered sufficient for the purposes at hand; but at the same time, outside of these purposes, they will be considered as themselves candidates for further explanation. In practical idiom, it will always make sense to ask if we wish, how I Donald Davidson, 'Mental Events', in Foster and Swanson, Experience

and Theory (Duckworth, I970).

77



78 STEPHEN WILLIAMS:

the cause brings about the effect-or, more formally, why the covering law relates the variables it does in the form it does. This rnuch at least is implied by our characterisation of a connection as causal. We may not of course have, or even have clues about, the explanation. But what would undermine our application of the concept of cause, would be to assert that there simply is no further explanation, that the request for one is just misplaced in this case-in short, that there are some causal regularities which, like the chance associations that may mimic them, just happen to be so. It is one implicit criterion of the former against the latter, that further explanation is appropriate. And it become more or less explicit where we already know on other grounds that an association is causal-for example, where we can manipulate the variables.

If these remarks are sound, what they exclude as incoherent is the notion of 'brute' causality: that some objective events could be related by a species of causal interaction no descriptions of which admit of any further non-trivial explanation. A causal law might be a brute fact, but only with respect to other propositions or hypotheses which presuppose it, or generally with respect to certain states of our knowledge-ultimate explanans theories not being causal.

A perennial and intractable element of the mind-body problem is immediately underlined when one considers the simplest causal interactions between physical events and sensations, such as being stuck with a pin causing a sharp pain. Aside from such views as parallelism, all the other classical accounts of the mind-body relation acknowledge this area of causal commerce, but are quite at a loss to suggest anything about the underlying nature of these connections. And this has all the appearance of being a permanent roadblock, so much so that unconvincing attempts have been made to exhibit it as a pseudo-problem. An epiphenomenalist, for example, would say that while the causal connection between physical stimuli and physical effects is essentially unproblematic and capable of further explanation through neurophysiology, the accompanying production of sensation (itself causally impotent) just has to be accepted as simple and inexplicable. This does not even look like an answer and, if I am right, is not really a coherent position at all. In general, no satisfactory rationale has been offered for these humdrum causal facts of our existence. The lack of a single comprehensive theory of the mental and the physical, a



PAINS, BRAIN STATES AND SCIENTIFIC IDENTITIES 79

consequence of the different sets of concepts appropriate to each realm, is not in this instance a rationale, but a problem. We cannot here just accept the fact of two separate sets of concepts, since in this case we cannot even see how they are properly related in their respective applications.

Now I suggest the most compelling prima facie ground for favouring a type-identity schema against its empirically equivalent rivals, is just that it alone might offer a way out of the perplexity of the causal connection: not by abolishing it, but by giving a physical description to both relata. In this way, if at all, might the simple everyday psychophysical laws connecting physical stimuli and sensations be further explained, in an underlying physical vocabulary. In polar contrast to Davidson's considerations, the problem forced on us here, which type identity may solve, is precisely that sensations, unlike thoughts and wishes, do show striking and detailed parallelism with the physical.

I shall start by quickly removing two spurious kinds of appeal which have sometimes been cited in favour of identity: they have only to be stated to be rejected. Both go under a certain flag called Occam's razor, and have done disservice to it. First, if two variables x and y behave in such a way that the rival explanations of constant correlation and identity are equivalent in empirical consequences, it has been implied that there is somehow a maxim that the identity explanation has it (because it involves fewer 'entities'?). And second, there is sometimes an appeal to the 'Unity of Science' which says in effect that since more and more disparate phenomena seem to be explicable in terms of a basic unified physical theory, then when we meet some particularly intractable phenomenon (such as sensations or secondary qualities) we may on inductive grounds take the wish for the deed and assume it can be banished or transformed into something more amenable simply because it is intractable. It is hardly surprising that Jaegwon Kim1 has accused identity theorists of using the 'mere slogan' of ontological parsimony to clothe their claims in a spurious garb of scientific methodology.

Kim and Brandt are among the very few philosophers I know who have analysed methodically and carefully the identity theorists' appeal to Occamist parsimony, and the putative analogy

I Jaegwon Kim, 'On the Psycho-Physical Identity Theory', Am. Phil. Quart. I966, and Richard Brandt and Jaegwon Kim, 'The Logic of the Identity Theory' Journal of Philosophy, September I967.



8o STEPHEN WILLIAMS:

with reductive scientific explanation: and they conclude that both claims collapse. r believe, however, that the picture they construct is seriously incomplete, and that as a result their conclusions are mistaken on both counts. Take the standard textbook paradigm of reductive scientific explanation, the explanation of the empirical Gas Laws by kinetic theory and statistical mechanics. The Boyle-Charles Law relates state variables of an ideal gas- temperature, pressure, volume-by simple mathematical statements. This Law, the fact that it has the form it does and applies to actual gases within the limits it does, is a candidate for explanation in turn. This is achieved through a bridge law expressing an experimentally verifiable relationship (2E/3 = kT) between absolute temperature and a variable of a quite different domain, mean molecular kinetic energy. With the aid of this further premiss the Boyle-Charles Law is formally deducible from the kinetic theory of matter, a theory of greater generality and wider empirical entailments (and, when this theory was later described by the theory of probability it explained not only the Gas Laws but the degrees of variation from them shown by some actual gases).

Considered in isolation, the bridge law which shows the mean kinetic energy of molecules to be proportional to absolute gas temperature, allows deducibility of one set of laws from the other. So far, no further deducibility, no increase in predictive power, is achieved by interpreting the bridge law as expressing identity of temperature with molecular kinetic energy. Kim fastens on to this point in attempting to show that an identity interpretation- in this case property identity-is idle: all the explanatory work is done, he maintains, by the statement that the properties are coextensive: a gas has temperature T if and only if it has molecular kinetic energy E. And, by analogy, the properties of having a pain and of being in brain state B need only be considered likewise coextensive, not identical.

It is true that the explanation does not, and logically cannot, assert identity of 'properties' in the sense Kim requires, which is nothing less than synonymy of the temperature and kinetic energy predicates. But it is also true that it does not assert coextensiveness either, since it is at best scientifically misleading, because vacuously circular, and at worst meaningless to ascribe temperature directly to a group of molecules. Now if mathematical deducibility of one set of laws from another were the only element in the explanation, then it would after all remain a perfectly proper



PAINS, BRAIN STATES AND SCIENTIFIC IDENTITIES 8I

question to ask, why the variables of the Gas Laws are correlated so exactly with the kinetic energy of molecules, i.e. why there is a bridge law at all and why it has the form it does. But it is not a proper question, and anyone who asked it would merely exhibit insufficient understanding of the relation between the Gas Laws and kinetic theory. There is a proper explanation terminus here. Accompanying the bridge law in the textbooks is the explicit identity assumption, that a given volume of gas may be considered as a cluster of molecules.' If it is conceptually in order to suppose volumes of gas identical with systems of molecules-and the whole theory presupposes it is-then the previously primitive gas variable terms such as temperature can be suitably defined (though not intensionally) in terms of the wider molecular theory, and the previously independent Gas Laws shown to be particular instances of this theory. Colloquially, gases obey the empirical laws they do, to the extent that they do, because they are systems of molecules. The question of why temperature and molecular properties are coextensive does not now arise: the state of a gas being at a certain temperature is, by assumption, identical with the state of the molecules having a certain kinetic energy.

Of course, the predicates descriptive of gases are not synonymous with the predicates of molecular theory, and it is easy to see that no genuine explanation could have been achieved if they were. Kim, I believe, creates unnecessary difficulties by his own clearly stipulated rule that state or event identity requires identity of properties, interpreted intensionally as synonymy of predicates. Thus, while he agrees-as presumably he must-that the paradigm reduction of thermodynamics to statistical mechanics involves economy in the number of independent primitive assumptions, it is not easy to understand what he takes these economies to be, having put himself in the position that a gas being at temperature T is a different but correlated event from its molecules having corresponding kinetic energy E. But this apparently opens the door to the confused and illicit question of how this correlation is to be further explained. It is presumably because of his ontology of intensionally defined events, that he insists that some psychophysical statements, including irreducibly psychological predicates,

I More fully, it is that a given volume of gas may be considered as a cluster of molecules behaving as Newtonian point-masses: and that the volume may also be considered subdivided into smaller volumes, each of which can contain all the possible discrete velocities in the total range of molecular velocity.




must appear in any explanans theory, however ultimate, of mental- physical correlations. But this would clearly imply in the analogous Gas Law case, that some statements mentioning temperature or its synonym would have to appear in any ultimate explanans theory of gas behaviour, which is patently false and explicitly denied by Kim. Can the analogy now be corrected in a way which would sustain the claim of an identity assumption for sensations and brain states to be clearly superior to its main rivals in its ability to explain agreed facts? I shall try to sketch the schema in which this would be exhibited (a schema which is of course empty if their candidature for identity is excluded on other grounds).

At an ordinary experimental level there are a host of empirical laws, quantifiable and capable of elaboration, which capture among other things such incontrovertible facts as that a person being pricked or burnt in a certain way causes a pain of a certain character, and so on through the range of bodily sensations. These laws will depend on procedures using special observational indices but essentially they will connect standard stimuli not solely with bodily responses, but also with reported sensations, that is, genuine inner episodes. And they will be repeatable, the possibility of individual lying neutralised by large samples.

Now at the more detailed neurophysiological level (no knowledge of which is implied by the above) we know for example that the destruction of tissue and strong stimulation of the smaller nerve fibres, corresponding to being pricked with a needle, causes certain patterns of electrochemical effect in the nervous system which invariably occur when subjects report themselves in pain. We can also trace fairly detailed correspondences of variables between the neural events and the independently distinguishable character of the concurrent sensations (though these are likely to be one-many rather than one-one correspondences). Thus, in addition to the simple empirical laws connecting gross stimuli with reported sensations, there are in effect bridge laws stating correspondences which allow the sensations (for example, a sharp throbbing pain lasting from t1 to t2) to be successfully predicted from the detailed character of the neural patterns alone. And, given the uncontentious identity of the gross stimuli with their finer- grained counterparts (mentioned above), such bridge laws provide the premisses whereby the simple empirical laws can be deduced from the underlying neurophysiological theory.

Now although this comic strip outline may not endear me to




neurophysiologists, it is one which is so far without prejudice to any particular mind-body position. The empirical consequences- in this case the predictive power of the neurophysiology-are clearly unaffected. But now the natural question with which I began, namely why the empirical laws connecting gross stimuli and sensations hold in the form they do, is supplemented by another question: why should there be such striking correspondences between the neural states and the prima facie quite different sensation episodes reported by the subject? These correspondences, which we are assuming are strong and pervasive enough actually to permit deduction of one set of laws from the other, so far present themselves as mere brute facts that cry out for explanation. But epiphenomenalism or Cartesian interactionism have none to offer.

Obviously, considerable explanatory simplification would be achieved if it is permissible to propose, as an appendix to the bridge laws in the manner of the Gas Law case, general identities between the states of a person, so that the state of being in pain is identical with that of being in a certain class of neural state. For then, the detailed pain variables (dull, throbbing, shooting, etc.) could be defined, extensionally of course, in terms of their neurophysiological counterparts, and the manner in which physical events bring about sensations, clearly explained. The ordinary experimental laws could be considered not simply as deducible from, but as particular instances of, the more general neurophysiological ones: a throbbing pain occurs in just the conditions it does because it is an identifiable state of activity of the nervous system.

I am deliberately not tying the identity to a localised state of the brain. Far more than this may be involved, and I would want to individuate the physical state of a person to allow flexibility to neurophysiology. If of course no independently delineable set of neural conditions is demonstrable when and only when- the person experiences pain (including of course phantom limb cases), then the identity will fail for empirical reasons.'

One obvious disanalogy with the Gas Law case is that here the proposal is of identity between independently identifiable particular states of an entity (a person) and not between entities themselves. The assumption presupposes a satisfactory sense in which persons are identical with living and characteristically

I See in this connection, R. C. Solomon, 'Doubts about the Correlation Thesis', Brit. J7nl. for the Philosophy of Science, March 1975.




functioning human organisms, but this can be distinguished from the strong entailment claims of physicalism and acceptably rendered along the functional lines of Wiggins (so that if brain transplants were to occur, the state of which particular hybrid nervous system is identical with person A being in pain, is decided by which amalgam preserves the necessary character continuity).

There are indeed other disanalogies. But, if they can be dealt with, it seems to me that some variant or other of this framework of putative theory, contains the essential and valid grounds which uphold identity against alternative mind-body accounts. Always provided that neurophysiology continues to develop in a way which exhibits correspondences and predictability of the varieties of experienced sensations, I believe that the pressure towards an identity theory along the general lines set out here will continue to be felt.

III

I shall not confront separately the question whether semantic category differences prohibit as senseless the very proposal of type identity between neural states and sensations. For this paper, consideration of the formally distinct Leibniz's Law objections may suffice, since these have frequently included such features as the privacy of sensations, which have also been quoted as criteria of their supposedly separate categorial status. What is not always noticed is the way that conflation of these two kinds of appeal can weaken instead of strengthen the objection. One does not need to appeal to Leibniz's Law if the items are obviously in different categories; and conversely, if the differential properties are such as to suggest such radical differences of type, then the correct application of Leibniz's Law as a decision procedure is very unlikely to be intuitively straightforward.

Just this, I suggest, occurs frequently in the identity debate to create the impression-misleading but immensely powerful-of decisive, almost self-evident falsifying differences in the candidates for identity. It is agreed that in this case, unlike that of the Morning and Evening Stars, identity is not an empirical thesis. There are no empirical criteria for identifying a person's state of pain which will show it to be numerically the same, or a different, state from the relevant correlated state of his nervous system. Ihaving noted this, some philosophers have been persuaded to




opt for mere correlation as against identity by t-he sheer prima facie difference between the two items, by what they have simply called the implausibility of identity. But if intuitions of plausibility or implausibility mean anything, they presumably presuppose that the proposition in question is logically, conceptually, possible. In clear cases of prohibitive category differences-say, the identity of the number 7 with some spatio-temporal particular-the proposition is not implausible, but nonsense. For the dimensions of plausibility, likelihood, probability, to gain any application they cannot coherently be combined with arguments for category distinctions or necessary truth or falsehood. And in the case at hand, the intui- tion of implausibility would seem to imply that the decisive differences between pains and brain states are a contingent matter: that it is possible, but in fact false, that pains might have the properties ascribed to brain states (or vice versa).

Now in a certain sense, this is all right. The earlier arguments by analogy with the Gas Law case are an appeal to plausibility, and they use contingent facts about sensations and brain states: it is presumably contingent that sensations have the relational properties entailed in their systematic correlation with brain states. But the properties usually cited as an objection to identity are not relational, and the fact that sensations have them is very difficult to represent as at all a contingent matter. As an objection to identity this line of argument becomes increasingly curious on examination.

What in fact are the crucial differential properties? We can leave aside as irrelevant to Leibniz's Law appeals to modal properties such as being necessarily owned, or to intentional ones such as being incorrigibly known to the owner. The remaining appeal is then either to the simple manifest fact that pains are not experienced as brain states; or, a different and less question- begging claim, that brain states just do not have the directly experienced phenomenal properties pains have. (And, since it is conceded that there is no empirical difference between identity and correlation, this has to be construed as a matter of phenomenological inspection which is both subject to intersubjective agreement, yet excluded from empirical relevance.)

The confusions embodied in this compelling conviction can be brought out by some brief science fiction. For can we conceive, as presumably we should be able to, what it might be like if the facts were different and pains were actually experienced as brain




states? It might be thought that after-images, which are experienced as colour expanses, provide an illustration: but they do not, since pains are not experienced on the model of any public perceptible object. Nor are brain states perceptible, though they are indi- rectly observable. Well, what might be envisaged are patterns of painful happenings experienced inwardly from time immemorial and of such a distinct structural character that, when neurophysiology eventually develops, investigators with their instruments immediately recognise certain neural patterns as those they have always experienced as pains, even before the experimental subjects corroborate them (which they later do). Nothing the subjects report has been falsified, but with the rise of science their pains have been detected as brain states, having additional electrochemical properties not previously realised. But, far from being counterfactual, something like this is what has actually happened, or soon may. Are not the sequential patterns of experienced pain- their intensities, throbbings, sudden spasms etc.-likely to prove quite suitably isomorphic with discovered patterns of neuron firings? This at least is the general assumption. What more manifest similarities are lacking, to sustain the claim that we do not, though we intelligibly might have, experienced pains as brain states? It is idle to suggest that nonetheless the subject is aware, not of rhythmic surges of electrical current, but rhythmical surges of pain. For what else could he be aware of? The grammar of our sensation language is such that even if-extending the science fiction-the investigator could connect his own nervous system with the instruments so that for each pattern of pain experienced by the subject, he experiences a precisely duplicated simultaneous pattern of pain, this would still be necessarily his numerically distinct pain and not the subject's. Again as a matter of grammar, he could not be observing another's pain through his instruments, but only his own, by having them.

Now as a story about how identity could be discovered, this science fiction is wrong. But it certainly is not wrong because of any implausibility of identity, because the deliverances of first- person experience exhibit pains as unlike brain processes, for plainly they do nothing of the sort. To give clear substance to the claim of implausibility one would have to be able to construct a counterfactual case of a far more fundamental kind-a possible world in which the facts of existence were somehow the grounds of certain altered conceptual rules for what were still, essentially,




sensations: and such that these alterations placed them sufficiently close to the category of public objects for them to be experienced, or empirically discovered, to possess or lack common properties.' We are likely to recoil from any such exercise, not only because of its implied hubris but because of the force our actual grammar of sensations properly exerts. The conviction that, regardless of what might possibly be discovered, pains are obviously nothing like brain states, is of a piece with the conviction that in any possible world, sensations could not be open to redescription in the manner of public objects, and stems from the grammatical fact that sensations have no room to be other than as experienced. No logical gap can open between how they seem and how they are: and this of course undermines their claim to be genuine objects of observation or recognition at all.

A long epistemological tradition, which has influenced the materialist debate, has assimilated sensations such as the having of a pain to other private episodes such as having an afterimage, and been impressed by the incorrigibility associated with these experiences, which has seemed to be grounded in direct acquain- tance with 'phenomenal' qualities. Thus, the experience of a sudden stabbing pain has been treated as virtually interchangeable with that of a round red afterimage for the purposes of debate. But a class of 'objects' for which there can be no distinction between their being b and seeming b, indeed between their occurring and merely seeming to occur, is one to which error and correctness are inapplicable, and which, if Wittgenstein is right, fails the minimum conditions of public reference. Now I would argue that sensations proper, such as pains, if construed as phenomenal items in the above sense, do indeed fail in just this way. By contrast, even afterimages, though experienced by one and only one person, escape the limbo of complete privacy simply because the concepts applicable to them-phenomenal qualities-are secondary extensions of public perceptible qualities. A red round afterimage has its substantial phenomenal character solely in virtue of the fact that it seems like, hence could be mistaken for, an objective red round surface. Conversely, what seems to me

The objections I am arguing against here are pre-Kripkean, but it is not difficult to see the general lines of reply to Kripke's arguments against identity. The fault lies not with Kripke's technical instruments but in his uncritical view of pains as phenomenal objects immediately and incorrigibly recognisable by only one person, yet in just the same way rigidly designated in a language of public reference. (Cf. Kripke, Naming and Necessity, pp. 337-342)-




a red round afterimage may actually be a blue surface in unusual light.

Now if this is right, sensations such as pains, whose descriptions are not extensions of those of public objects, cannot for that reason have phenomenal properties. They cannot, that is, have properties of the kind ascribable primarily to public objects and secondarily to 'appearances'-to the way perceptual phenomena are said incorrigibly to look, taste, hear and feel to the touch. (And this 'incorrigibility', misleadingly so called, need not detain us: the sense it clumsily captures is merely that to transfer the ordinary possibility of mistake to qualify the way things seem would, by hopeless regress, destroy the very conditions for coherent perceptual error and correctness about how they are.)

For this reason it seems a serious confusion to construe the having of a sensation on the model of observing or recognising some object. Since no such construal could enable us to talk of experiencing a sensation accurately or inaccurately, clearly or confusedly, it would be better not to consider them as intentional episodes at all-or at any rate, to use Anscombe's terms, to be clear that there is no room for contrast between the intentional and the material object of feeling, as there is in ordinary perceptual sensing. Thus, while the experience can of course be reported and described by the person, what is reported is not itself a mental act of having, grasping, feeling, sensing or recognising an accusative mental object which is a pain or tickle. For it to be true that A has a darting pain is necessarily for A to experience it under just that description: which is to say that 'experience' has here a different sense from when he experiences an afterimage, which he might have experienced as a patch on a wall. The sense in which A experiences a pain as a pain is without contrast and really redun- dant. Given only A's ability to use the word correctly, he does not then take what he feels to be a pain, save in the quite empty sense that it is necessarily what he takes it to be. If this is right, sensations cannot be considered as a form of intentional access to ineffably vivid raw feels of which public observation knows nothing, nor as a special species of sense informing us of our bodily states-as some, including materialists, have proposed. Sensations are objectless.

To deny a separate object for sensations to be about, is not of course to deny that these experiences have a distinct character, describable in quite a rich language. Moreover, this formn of




description is very different from the case of self-ascription of other mental states (believing, intending etc.) where we are not even tempted to think of inner recognition. We describe sensations in terms which have seemed to be, but are not, a species of primitive terms for intrinsically sensed qualities. Pains are throbbing, clenching, shooting, darting, burning, stabbing and so forth. But the clenching of a pain, unlike the redness of an afterimage, is not even a secondary extension of that literal property of public objects such as pincers or talons, but is entirely a metaphor. (Other common predicates, such as intense, intermittent and perhaps, for example, throbbing, specify a relational mode or pattern of events which is indifferent as to the determinate process under description.) It has been debated whether and where the metaphor has derived from common external stimuli which cause those sensations (stabbing, pinching), or using the illustrations of other familiar processes (darting, shooting). But the central point is that where they are not purely relational, such descriptions are all metaphors using descriptions of public phenomena, as indeed they must be if they are to succeed in describing at all. As predicates they could not be primitive, in the way that perceptual predicates such as colour terms-applicable to material objects, not sensa-are primitive.

It should scarcely need emphasising that, having acknowledged this necessarily metaphorical status, one must resist all temptation to suppose implicitly that the metaphors might somehow be cashable, that something which is hidden might be capable of a more informative description: for this would transgress the very grammar of our sensation language. All we can say is: we find these metaphors useful. Unfortunately, a version of this mistake is made in the translation attempts of topic-neutral materialists. Apart from other grave difficulties, they are compelled to represent sensation reports as reports of objects that are puzzlingly elusive and indefinite. Worse, the implication is that this indefiniteness -is for empirical reasons: our inner sense just is not discriminating enough to pick out their intrinsic neural character. This approach conflates reports of sensations with naive empirical reports at a pre-scientific level, as if reporting pains is much like reporting a vague illness which awaits more precise diagnosis. But the subject can never come to acknowledge his state as an awareness of some scientific object, for our sensation language is neither an observation language nor a theoretical one. Sensation terms are not




capable of revision or further filling out by scientific concepts without losing their very role in first-person description. They are complete as they are; and nothing is hidden.

Having a pain is an experience, but the pain is not an object of experience, nor is 'painful' a phenomenal predicate. And the more detailed predicates applicable to the experience are neither phenomenal nor primitive, but consist of necessarily non-cashable metaphor. Now it seems clear that these do not constitute the crucial differential properties which would debar the identity of sensations with neural states by Leibniz's Law. Provided syno- nymies are nowhere being proposed (as they are not being proposed in the Gas Law case) there is no reason why the more detailed features of the experience should not be defined extensionally in terms of their isomorphic neurophysiological counterparts. (None of this, of course, need involve illegitimate mixing of the two sets of concepts, which would occur if one committed the sin of thinking some specific pattern of neuron firing as the determinate object whose features our sensation predicates describe only metaphorically.) Such definitions would accompany the assumed identity of a person's state of pain with a certain state of his nervous system, which would then allow explanation of the ordinary empirical laws which cover the simple production of a pain by an external stimulus.

But, as already indicated, neurophysiological concepts could not, either by stipulation or usage, acquire the role of sensation concepts, with the latter's anchorage in first-person avowals and reports. And at this point I should affirm what I think is primitive to sensation concepts. When the private phenomenal beetles in the boxes cancel out, what remains is emphatically not overt bodily behaviour. It is the ineradicable experience of a person being hurt, an experience he wants to stop and requires no further reason for wanting to stop, on penalty of radical incomprehension. But hurting is not a phenomenal property: if it were, its connections with these characteristic desires and actions would be purely contingent. But in that case it is difficult to see how such connections could ever be established, since no behaviour could be-as it is-internally connected with first-person experience in such a way as to constitute an adequate expression of it. The concept of being in pain is internally bound into a set of concepts such as suffering, injury, avoidance, and is possible only to sentient beings sharing a form of sensibility. This is grounded in a common



PAINS, BRAIN STATES AND SCIENTIFIC IDENTITIES 9I

nervous system but also in agreements in judgements: so that while, for example, it is possible to locate the neurophysiology of humans more precisely within the broader basis of evolutionary biology, no such extension of the concepts of sensations is intel- ligible beyond possible membership of our forms of life.

If, therefore, reductive explanation is taken to involve full translation of one system of concepts into another, then our concepts of sensation are not reducible. But nor, be it noted, are our concepts of material objects. Scientific reduction standardly permits the terms of one formally articulated theory to be defined by those of another more general one; and our sensation concepts are not a theory. But I have suggested that the experimentally established laws which capture mundane causal interaction between physical events and sensations do constitute a theory in the appropriate sense. The terms appearing in them are a specialised and idealised version of the terms of ordinary use. They may for example be expressed as quantities functionally related to pupillary response or other variables which have no place in our ordinary sensation concepts. But they will be unambiguously derived from those concepts, and grounded firmly in the first-person reports of the experimental subject. It is the specialised versions which may come to be defined extensionally by their neurophysiological counterparts. Once again, parallels suggest themselves with the case of macro-objects and collections of molecules.

A material object is assumed to be a collection of molecules, although our concept of a material object is not the concept of such a collection (material objects are continuous, coloured etc.). How- ever, the empirical concept which appears in the-usually mechanical-laws for which molecular theory offers explanation, does not coincide precisely with the ordinary perceptual concept of a material object, but is rather a stipulated idealisation of it, in which the mathematically expressible properties are fundamental and others deliberately neglected. It is this formalised version of a material object which is assumed identical with a collection of particles having no perceptual properties at all-which assumption effects an important explanatory economy within the framework of the theories by avoiding the need for a range of previously independent predicates (in the example, temperature predicates). But our full-blooded perceptual concept of a material object remains unitary and irreducible. Its role cannot be taken over by the concepts of micro-theory, as some philosophers have proposed,



92 STEPHEN WILLIAMS: SCIENTIFIC IDENTITIES

since it is inseparable from the whole form of experience which makes possible agreements in perceptual judgements, hence objectivity, hence observation.

There is, then, some similarity between the two cases in the important respect that both sensation and material object concepts are anchored in conceptual frameworks that do not seem open to wholesale replacement by scientific ones (material object concepts are, but sensation concepts are not, themselves pre- supposed in the rules of constructing scientific theories). But in neither case does this prohibit important explanatory advances being achieved by identifying their objects with other ranges of object.

IV There remain serious omissions. In particular, I have construed both pains and neural states under the weak sortal state of a person, but have shirked the necessary task of a formal account of state identity. I have also shirked the very troublesome question of the bodily location of sensations, which is difficult to accom- modate in the view I adopt.

Davidson's argument was for token identities between neural events and essentially intentional mental events such as the having of a thought-a thesis which seems in advance intuitively accept- able. I have argued that the very features which seemed to mark sensations such as pains as indubitably and quintessentially non- physical, in fact undermine the genuine possibility of ascribing the crucial phenomenal properties which appeared to falsify identity. But clearly, neither argument gives any comfort to the desire to identify genuine perceptual states (such as the normal seeing of a red tomato) with brain states. More than any other obstacle, it is the primitive objective character of perceptual predicates-the reds and greens-which threaten to sink the enterprise of a fully comprehensive materialism.



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Pains, Brain States and Scientific Identities

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