Paper for Buffalo, NY conference will be abstracted from this paper.

Scheduled to appear in Chomsky and His Critics ed L. Antony and N. Hornstein, Blackwell Please do not quote without checking with me - I may have changed my wording or my worldview.

1 Introduction

Materialism is the view that every thing and event in the universe is physical in every respect, that "physical phenomenon" is coextensive with "real phenomenon", or at least with "real, concrete phenomenon". For the purposes of this paper, I am going to assume that it is true.

It has been characterized in other ways. David Lewis once defined it as "metaphysics built to endorse the truth and descriptive completeness of physics more or less as we know it", and this cannot be faulted as a terminological decision. But it seems unwise to burden materialism - the view that everything in the universe is physical - with a commitment to the descriptive completeness of physics more or less as we know it. There may be physical phenomena which physics (and any non-revolutionary extension of it) cannot describe, and of which it has no inkling, either descriptive or referential. Physics is one thing, the physical is another. "Physical" is the ultimate natural-kind term, and no sensible person thinks that physics has nailed all the essential properties of the physical. Current physics is profoundly beautiful and useful, but it is in a state of chronic internal tension. It may be added, with Russell and others, that although physics appears to tell us a great deal about certain of the general structural or mathematical characteristics of the physical, it fails to give us any real insight into the nature of whatever it is that has these characteristics - apart from making it plain that it is utterly bizarre relative to our ordinary conception of it.

It is unclear exactly what this last remark amounts to (is it being suggested that physics is failing to do something it could do?), but it already amounts to something very important when it comes to what is known as the "mind-body problem". Many take this to be the problem of how mental phenomena can be physical phenomena given what we already know about the nature of the physical. But those who think this are already lost: we have no good reason to think that we know anything about the physical that gives us any reason to find any problem in the idea that mental phenomena are physical phenomena. Joseph Priestley saw this clearly over two hundred years ago, and he was not the first. Noam Chomsky reached essentially the same conclusion thirty years ago, and he was not the last. Most present-day philosophers take no notice of it and waste a lot of time as a result.

2 Terminology

I am going to use the plural-accepting, count-noun form of the word "experience" for talking of experienceS as things (events) that may (and presumably do) have non-experiential being as well as experiential being. And I am going to reserve the adjective "experiential" and the plural-lacking form of the noun "experience" for talking about the qualitative character that experienceS have for those who have them as they have them, where this qualitative character is considered wholly independently of everything else. The phenomenon of experiential qualitative character is part of what exists - it is part of reality, whatever its ontological category - and it is essential to have some unequivocal way of referring to it and only to it.

One could express this terminological proposal by saying that "experiential phenomena" and "experience" (plural-lacking form) refer in a general way to: that part of reality which one is left with when, continuing to live and think and feel as one does, one engages in an old sceptical thought experiment and imagines that the "external world", including one’s own body, does not exist. They refer to the part or aspect of reality one has to do with when one considers experienceS specifically and solely in respect of the experiential qualitative character they have for those who have them as they have them, and puts aside the fact that they may also be correctly describable in such non-experiential terms as "a 70-20-30 Hertz coding triplet across the neurons of area V4".

It is easy to forget the force of this ruling, and I will mark it by giving "experiential" a capital letter.

3 Realistic materialism

Realistic materialists - realistic anybodys - must grant that Experiential phenomena are real, concrete phenomena, for nothing in this life is more certain. They must therefore hold that they are physical phenomena. It may sound odd to use the word "concrete" to characterize the qualitative character of experiences of colour, gusts of depression, thoughts about diophantine equations, and so on, but it isn’t, because "concrete" simply means "not abstract". For most purposes one may take "concrete" to be coextensive with "possessed of spatiotemporal existence", although this will be question-begging in some contexts.

It may also sound odd to use "physical" to characterize mental phenomena like Experiential phenomena: many materialists talk about the mental and the physical as if they were opposed categories. But this, on their own view, is like talking about cows and animals as if they were opposed categories. For every thing in the universe is physical, according to materialists. So all mental phenomena, including Experiential phenomena, are physical phenomena, according to materialists; just as all cows are animals.

So what are materialists doing when they talk, as they so often do, as if the mental and the physical were different? What they presumably mean to do is to distinguish, within the realm of the physical, which is the only realm there is, according to them, between the mental and the non-mental, or between the Experiential and the non-Experiential; to distinguish, that is, between mental (or Experiential) features of the physical, and non-mental (or non-Experiential) features of the physical.

It is this difference that is in question when it comes to the "mind-body" problem; materialists who persist in talking in terms of the difference between the mental and the physical perpetuate the terms of the dualism they reject in a way that is inconsistent with their own view. I use the words "mental" and "non-mental" where many use the words "mental" and "physical" simply because I assume, as a (wholly conventional) materialist, that every thing and event in the universe is physical, and find myself obliged to put things in this way.

There is tremendous resistance to abandoning the old mental/physical terminology in favor of the mental/non-mental, Experiential/non-Experiential terminology, although the latter seems to be exactly what is required. Many think the old terminology is harmless, and a few are not misled by it: they consistently use "physical" to mean "non-mental physical". But it sets up the wrong frame of thought from the start, and I suspect that those who are never misled by it are members of a small minority.

When I say that the mental, and in particular the Experiential, is physical, I mean something completely different from what some materialists have apparently meant by saying things like "experience is really just neurons firing". I don’t mean that all aspects of what is going on, in the case of conscious experience, can be described by current physics, or some nonrevolutionary extension of it. Such a view amounts to radical "eliminativism" with respect to consciousness, and is mad. My claim is different. It is that the Experiential (considered just as such) - the feature of reality we have to do with when we consider experiences specifically and solely in respect of the Experiential character they have for those who have them as they have them - that "just is" physical. No one who disagrees with this is a remotely realistic materialist.

When aspiring materialists consider the living brain, in discussion of the "mind-body problem", they often slide into supposing that the word "brain" somehow refers only to the brain-as-revealed-by-current-physics. But this is a mistake, for it refers just as it says, to the living brain, i.e. the living brain as a whole, the brain in its total physical existence and activity. Realistic materialists must agree that the total physical existence and activity of the brain of an ordinary, living person, considered over time, is constituted by Experiential phenomena (if only in part) in every sense in which it is constituted (in part) by non-Experiential phenomena characterizable by physics.

4 Materialism further defined

Materialism is the view that every thing and event in the universe is physical in every respect, but a little more needs to be said, for Experiential phenomena - together with the subject of experience, assuming that that is something extra - are the only real, concrete phenomena that we can know with certainty to exist, and this definition fails to rule out the idealist view that mental phenomena are the only real phenomena and have no non-mental being. It would, however, be silly to call this view "materialism". Russell is right to say that "the truth about physical objects must be strange", but it is reasonable to take materialism to be committed to the existence of non-mental, non-Experiential being in the universe, in addition to mental Experiential being.

It is also reasonable to take materialism to involve the further claim that every thing or event in the universe has non-mental, non-Experiential being, whether or not it also has mental or Experiential being. Applied to mental phenomena, then, materialism claims that that each particular mental phenomenon essentially has non-mental being, in addition to mental being. This is, I think, the standard view. Note that to distinguish between mental being and non-mental being is not to claim to know how to draw a sharp line between them. The starting situation is simply this: we know there is mental being, and we assume, as materialists, that this is not all there is.

All realistic materialists, then, take it that there is both mental and Experiential being and non-mental, non-Experiential being. Must all realistic monists also take it that there is non-mental, non-Experiential being? Many would say Yes, on the grounds that it is not remotely realistic to suppose either that there is, or might be, no non-mental or non-Experiential being at all. But the question of what it is to be (metaphysically) realistic is far harder here than it is when it is merely the existence of Experience that is in question. For the purposes of this paper I will assume that any realistic position does take it that there is non-mental or non-Experiential being in addition to mental and Experiential being, for this assumption accords with ordinary conceptions, and my main argument does not require me to challenge it. But it is at best an assumption. Idealists deny that realistic monism requires acknowledgement of non-mental, non-Experiential phenomena, and I will enter a number of reservations along the way.

It is clumsy to oscillate between "mental" and "Experiential", or constantly double them up, and in the next few sections I will run the discussion in terms of the mental/non-mental distinction (such as it is). This said, all my examples of mental phenomena will be Experiential phenomena, for they suffice to make the relevant point and are, in the present context, what matter most. It may be added that the reference of the term "Experiential" is much clearer than that of the essentially contestable term "mental", and that the latter may in the end deserve the treatment proposed for the term "physical" in §14 below. Nevertheless it seems best to begin in this way.

I will quote Russell - post-1926 Russell - frequently when discussing materialism, for my views converge with his in certain respects, and he has been wrongly ignored in recent discussion. He was still inclined to call himself a "neutral monist" at that time, but he is equally well read as a thoroughgoing materialist. He rejects materialism in name, pointing out that "matter has become as ghostly as anything in a spiritualist séance" - it has disappeared "as a ‘thing’" and has been "replaced by emanations from a locality" - , but grants that "those who would formerly have been materialists can still adopt a philosophy which comes to much the same thing. They can say that the type of causation dealt with in physics is fundamental, and that all events are subject to physical laws". And this, in effect, is what he does himself.

5 "Mental" and "non-mental"

It may seem odd to take "mental" as the basic positive term when characterizing materialism. But one is not a thoroughgoing materialist if one finds it so. For all materialists hold that every phenomenon in the universe is physical, and they are neither sensible nor realistic if they have any inclination to deny the reality of mental phenomena like Experiential phenomena. It follows that they have, so far, no reason to find it odd or biased to take "mental" rather than "non-mental" as the basic term.

"Surely it would be better, even so, to start with some positive term, say ‘T’, for the non-mental physical, and then define a negative term, ‘non-T’, to cover the mental physical; or use a pair of independently positive terms?" There are two good reasons for taking "mental" as the basic positive term, one terminological, the other philosophical. The terminological reason is simply that we do not have a convenient positive term for the non-mental (obviously we can’t use "physical", and there is no other natural candidate). The philosophical reason is very old: it is that we have direct acquaintance with - know - fundamental features of the mental nature of (physical) reality just in having experience in the way we do, in a way that has no parallel in the case of any non-mental features of (physical) reality. We do not have to stand back from experiences and take them as objects of knowledge by means of some further mental operation, in order for there to be acquaintance and knowing of this sort: the having is the knowing.

This point has often been questioned, but it remains immovable. Russell may exaggerate when he says that "we know nothing about the intrinsic quality of physical events except when these are mental events that we directly experience", or that "as regards the world in general, both physical and mental, everything that we know of its intrinsic character is derived from the mental side", for it is arguable that the spacetime character of the world is part of its intrinsic character, and, further, that we may have some knowledge of this spacetime character. I don’t think he exaggerates much, however. He is onto something important, and the epistemological asymmetry between claims to knowledge of Experiential being and claims to knowledge of non-Experiential being is undeniable, however unfashionable.

The asymmetry claim that concerns me is not the claim that all epistemic contact with concrete reality involves experience, and that we are inevitably a further step away from the thing with which we are in contact when it is a non-Experiential phenomenon. It is, rather, the claim that we are acquainted with reality as it is in itself, in certain respects, in having Experience as we do. This second claim revolts against the tendency of much current epistemology and philosophy of mind, but there is no reason why it should trouble thoughtful materialists, and I will offer a brief defence of it in §12. Here it is worth noting that it is fully compatible with the view that there may also be fundamental things we don’t know about matter considered in its Experiential being.

6 Aside: "as it is in itself"

Does one need to defend the phrase "as it is in itself", when one uses it in philosophy? I fear one does, for some think (incoherently) that it is somehow incoherent. Still, it is easy to do. The supposition that reality is in fact a certain way, whatever we can manage to know or say about it, is obviously true. To be is to be somehow or other. Nothing can exist or be real without being a certain way at any given time. And the way something is just is how it is in itself. This point is not threatened by the suggestion that our best models of the behaviour of things like photons credit them with properties that seem incompatible to us - e.g. wave-like properties and particle-like properties. What we learn from this is just that this is how photons affect us, given their intrinsic nature - given how they are in themselves, and how we are in ourselves. We acquire no reason to think (incoherently) that photons do not have some intrinsic nature at any given time. Whatever claim anyone makes about the nature of reality - including the claim that it has apparently incompatible properties - just is a claim about the way it is; this applies as much to the Everett "many-worlds" theory of reality as to any other.

Some think that what we learn from quantum theory is that there is, objectively, no particular way that an electron or a photon is, at a given time. They confuse an epistemological point about undecidability with a metaphysical claim about the nature of things. The problem is not just that such a claim is unverifiable. The problem is that it is incoherent. For whatever the electron’s or photon’s weirdness (its weirdness-to-us: nothing is intrinsically weird), its being thus weird just is the way it is.

So we may talk without reservation of reality as it is in itself. Such talk involves no (allegedly dubious) metaphysics of the Kantian kind. Its propriety derives entirely and sufficiently from the thought that if a thing exists, it is a certain way. For the way it is just is how it is in itself.

7 Structure and structured

So much, for the moment, for our theoretical conception of the mental: it has some securely anchored, positive descriptive content, and we can know that this is so; for whatever the best general account of it, it includes Experiential phenomena in its scope; and Experiential phenomena are not only indubitably real; they are also phenomena part of whose intrinsic nature just is their Experiential character; and their Experiential character is something with which we are directly acquainted, however hard we may find the task of describing it in words. This is so even if we can make mistakes about the nature of our experiences, and even if we can do so even when we consider them merely in respect of their (Experiential) qualitative character. It is so even if we differ dramatically among ourselves in the qualitative character of our experiences, in ways we cannot know about.

Our theoretical conception of the mental, then, has clear and secure descriptive content. (Don’t ask for it to be put further into words; the anchoring is sufficiently described in the last paragraph.) Our theoretical conception of the non-mental, by contrast, remains, so far, a wholly negative concept. It has, as yet, no positive descriptive content.

Can anything be done about this? On one reading, Russell thinks not: the science of physics is our fundamental way of attempting to investigate the non-mental being of physical reality, and it cannot help us. "Physics is mathematical", he says, "not because we know so much about the physical world, but because we know so little: it is only its mathematical properties that we can discover. For the rest, our knowledge is negative". "We know nothing about the intrinsic quality of physical events except when these are mental events that we directly experience". On this view, neither physics nor ordinary experience of physical objects give us any sort of knowledge of the intrinsic nature of non-mental reality.

Is Russell right? Something needs to be said about his use of the word "intrinsic", which is potentially misleading. It helps to consider other ways in which he puts the point. Thus he talks regularly of the "abstractness" of physics. The knowledge it gives is, he says, "purely formal". It reveals the abstract "structure" of physical phenomena while saying nothing about their "quality". . . .

I am not sure that the distinction between structure and quality is clear, or fundamental in such a way that it holds "all the way down", but (putting that doubt aside) it seems that the fundamental distinction that Russell has in mind can be expressed by saying that it is a distinction between how X is structurally disposed and what X is apart from (over and above) its structural disposition. Physics gives the structure, but not the structure-transcendent nature, of the thing that has the structure. If we say that truths about how X is structurally disposed have purely structure-specifying content, while truths about what X is over and above its structural disposition also have structure-transcendent content, or, more simply, non-structural content, then we may say that "non-structural" covers everything that Russell has in mind when he talks of the "intrinsic" nature of things.

One might dramatize Russell’s idea by saying that physics can be thought of as a formal system which remains, in a peculiar sense, an uninterpreted formal system, even though we know that it applies to something - reality, the universe - and even though it is elaborated in specific (and indeed causal) response to that something. On this "Ramseyfied" view, we may know that the universe has features that are structurally isomorphic to the structures delineated in the equations of physics, but we have no account of the non-structural nature of the thing that has the structure(s) in question.

So we are (to pursue the metaphor) in the peculiar position of having a known, concrete application (and so, in one sense, an interpretation) for a formal system, without that application constituting a model (in the sense of model-theoretic semantics) that can confer positive descriptive meaning on its terms. In being the subject matter of physics, the universe provides it with a merely referential model or object, of which it gives a merely structure-specifying description. Physics is about the physical, and may give a correct abstract representation of its structural disposition as far as it goes; but it does not and cannot tell us anything about what the physical actually is, over and above the fact that it exemplifies a certain formal structure.

8 The non-mental - space

The question rearises. Can physics endow our general theoretical conception of the non-mental with any positive descriptive (not merely referential) content? Russell thinks not. I disagree because correct structural description of a thing is already description of a feature of its intrinsic nature. But this disagreement is merely terminological, and the real question is this: Can one go any further than structure-specifying content, when attempting to give a satisfactory theoretical characterization of the non-mental? Russell in 1927 thinks not. It seems to me, however, that we may be able to go a little further. I’m inclined to think that our ordinary conception of space may get something fundamental right about the nature of reality as it is in itself, and hence about the intrinsic nature of reality - something that survives even after the finite-but-unbounded curved gravity-constituting spacetime of relativity theory (or the ten- or eleven- or twelve-dimensional spacetime of one of the leading versions of string theory) has been granted to be closer to the truth.

I am tempted to hold up my hands, like the kindly, irritating G. E. Moore, and to consider, not my hands, but the space between them, and to say: "This is space, and it is real, and I know its nature, in some very fundamental respect, whatever else I do not know about it or anything else (e.g. the fact that it is an aspect of spacetime)". On this view the ordinary concept of space, or indeed the concept of spacetime, in which (I claim) a fundamental feature of our ordinary conception survives, has correct non-structural descriptive content. It does not relate only to "what we may call the causal skeleton of the world", if to say this is to say that it does not capture any aspect of the non-structural nature of the world. It has non-structural content, and can transmit this content to our more general conception of the non-mental.

Russellians may object as follows. "This line of thought is profoundly natural, but it depends on a fundamentally false imagining. It involves the conflation of "objective" space, "space as it is in itself" (where this is taken as a merely referential, structure-specifying term with no pretension to non-structural content) with the phenomenological space (or spaces) associated with perception. It involves an almost irresistible but entirely fatal failure to "realize what an abstract affair form really is". All those, like yourself, who think that it is viable are "guilty, unconsciously and in spite of explicit disavowals, of a confusion in their imaginative picture of matter".

Some of those who take this line are suffering from excessive empiricism. They take it that the notion of space - or indeed shape - that we possess is essentially informed by the character of our sensory experiences, and in this I think they are mistaken. It may well be true that sensory experiences of specific kinds are necessary for the acquisition of concepts like SQUARE or SHAPE or SPACE, in the case of beings like ourselves. Such concepts can nevertheless float free of the different possible sensory bases of their acquisition and subsequent deployment, without ipso facto becoming "merely" formal or structure-specifying in character. It is easy to see that grasp of the content of SHAPE (say) does not require essential reference to any specific sensory experience. It suffices to point out that exactly the same concept of shape - i.e. the concept of shape, for there is only one - can plausibly be supposed to be fully masterable by two different creatures A and B on the basis of sensory experiences in entirely different sensory modalities familiar to us - sight and touch. One has to endorse a rather crude form of meaning-empiricism or concept-empiricism to suppose that A and B do not - cannot - have the same concept, as they do geometry together. A concept is not a faint copy or transform of a sensory experience. It is, precisely, a concept.

That’s one point. Another, crucial in this context, is that the concept of shape or space that A and B have in common is not an entirely abstract or purely formal concept, as the supporters of Russell seem to suggest. There is more to A and B sharing the specific concept SHAPE or SPACE than there is to their sharing mastery of the principles of an uninterpreted formal system that is in fact suitable for the expression of shape configurations or spatial relations although they know it only as an uninterpreted formal system. It is precisely because pure form is such a very "abstract affair", as Russell says, that the concept of shape or space that A and B can have in common in spite of their different sensory experiences cannot be supposed to be a matter of pure form. To think that it is a matter of pure form is to miss out precisely their grasp of the spatiality of space - of that which makes their grasp of the concept of space more than grasp of (say) an abstract metric. The concept has non-structural content.

NP It is abstract in one sense: it is abstract relative to all the particularities of sensation, in a way that is sufficiently indicated by reference to the fact that different creatures can acquire it (the very same concept) on the basis of experience in entirely different sensory modalities. It is indeed, and essentially, a non-sensory concept. But it is not purely abstract in Russell’s sense, because, to repeat, it involves grasp of the spatiality - rather than what one might call the mere abstract dimensionality - of space. Spatiality is not abstract dimensionality. The nature of abstract dimensionality can be fully captured by a purely mathematical representation. The nature of spatiality cannot.

Obviously questions arise about the precise nature of the non-structural content of concepts like SHAPE and SPACE. What more can be said about what it is to grasp the spatiality of space (given that SHAPE and SPACE may be fully shared by A, B, superbats, and others)? In the present context I am content to hold up my hands again. Empiricists press me. I question the question, offering (a) the suggestion that sensory modalities that differ qualitatively at first order (i.e. in the way that sight and touch do) may be said to be crucially similar at second order in as much as they are "intrinsically spatial" in character, (b) the speculation that perhaps this similarity can itself be understood as a matter of similarity of (Experiential) qualitative character, (c) the acknowledgement that it may be that one must be capable of experience in some "intrinsically spatial" sensory modality or other (even if only in imagination) in order to possess SHAPE or SPACE, (d) the reservation that even if a non-conceptual experiential modality must be in play, it is not obvious that this must be a sensory modality.

Russellians may be unimpressed. Michael Lockwood, in particular, is sympathetic to the idea that knowledge of spacetime structure is not knowledge of any feature of the "intrinsic" or non-structural nature of reality. In doing physics, Lockwood says, we may grasp the abstract structure exemplified by space while having "no conception of its content: i.e. what it is, concretely, that fleshes out this structure. (For all we know, on this view, Henry More and Newton may be right in equating space with God’s sensorium!)"

But I am prepared to grant this. I am prepared to grant that we cannot rule out the possibility that space is God’s sensorium, or something even more unknown, and that there is therefore a sense in which we may have no idea of what it is that "fleshes out" the abstract structure exemplified by space. For it may still be true that one grasps something fundamental about the non-structural nature of space in thinking of it as having, precisely, spatiality, rather than mere abstract dimensionality. If space is God’s sensorium, so be it: God’s sensorium may really have the property of spatiality. Between a fat-free, purely mathematical and thus wholly abstract representation of the structure of space and a partly structure-transcending conception of space as God’s sensorium (or some such) lies a third option: an ostensibly less rich but still structure-transcending conception of space as specifically spatial in its dimensionality. Some may think this a fine point, but it is (I take it) a huge step away from Russell’s view that "we know nothing about the intrinsic quality of physical events except when these are mental events that we directly experience".

I am not claiming that we do know something about the non-structural nature of space, only that we may (I hold up my hands, I move them apart). This claim allows, as it should, that there may well be more to space than we can know. SPACE, like PHYSICAL, is a natural-kind concept, and there are some atrociously good reasons for thinking that there is more to space than we know or can understand. Putting aside the (already weighty) points that physical space is non-Euclidean, and is itself something that is literally expanding, and the non-locality results, and questions about the nature of the vacuum, I for one can’t fully understand how space and time can be interdependent in the way that they demonstrably are. We are also told on very good authority that gravity is really just a matter of the ‘curvature’ of space, and that string theory is an immensely promising theory of matter (especially after the "second superstring revolution" and the growth of M-theory, and especially when it comes to understanding gravity) that entails that there are at least ten spatial dimensions . . . .

These points reopen the connection to the mind-body problem. For as they pile up, one can’t really hold on to the old, powerful-seeming Cartesian intuition that there is a "deep repugnance" or incompatibility between the nature of conscious experience and the nature of spatial extension - that "the mental and the spatial are mutually exclusive categories". We have direct acquaintance with fundamental features of conscious experience - Experiential features - just in having it; but we have no good reason to think that we know enough about the nature of space - or rather, about the nature of matter-in-space-considered-in-so-far-as-it-has-non-mental-being - to be able to assert that there is any repugnance. And if conscious experience is in time, as everyone agrees, then it is in spacetime, given the way in which space and time are interdependent. In which case it is in space in every sense in which it is in time.

9 The non-mental - spin, mass, and charge

I have proposed that our theoretical conception of the non-mental can acquire some non-structural content from its first lieutenant, the concept of space. Can it acquire any more? Well, I think that our more particular spatial concepts of shape, size, position, distance, and local motion (I raise my hands and bring them together) may also get something right about reality as it is in itself, and so contribute to the non-structural content of our general theoretical conception of the non-mental. I think, in other words, that Locke may be essentially right in his view that some of our ideas of primary qualities correctly represent how things are in themselves, although his account needs recasting. Somewhat less confidently, I am inclined to think that our ordinary conception of time gets something right about the nature of reality (both Experiential and non-Experiential) - even if we need to conceive time as part of spacetime in order to think about it properly.

Going on from space, time, extension, shape, position, distance, and motion, in the attempt to give a positive characterization of the non-mental, one may want to mention properties like spin, mass, charge, gravitational attraction, ‘colour’ and ‘flavour’ (in the quantum-theoretic sense). But one will have to bear in mind that our grasp of these things - any grasp of them over and above that which is conveyed by their intimate relation to spatiotemporal concepts - is expressed merely in equations; and the truth in Russell’s remark that physics is mathematical not because we know so much about the physical world, but because we know so little. So although I like to think that spatiotemporal concepts carry non-structural content, I do not think this can be true of any of these other concepts considered independently of their relations to spatiotemporal concepts. Here Russell is right: we know nothing of the non-mental non-structural nature of - for example - electrical phenomena apart from their spacetime structure; all we have are equations.

But even if knowledge of spacetime structure is all we have, in the way of non-structural knowledge of the nature of the non-mental, it makes a huge difference to the case. Consider the difference between a characterization of the forces of electrical attraction and repulsion in which their spatial character (the way they decrease with distance) is given a purely abstract-dimensional interpretation, and one in which it is given a genuinely spatial interpretation. Consider any account of anything in which time relations have a merely abstract representation, and one in which the temporality of time is genuinely represented.

I will now offer a further characterization of what it is to be a genuine materialist. But first I must first answer one more objection that occurs to many. ‘It seems to follow, from your claim that we have no knowledge of the non-structural non-spatiotemporal nature of things—of how things are—that we cannot know that there there are tables and chairs and hens and hens’ eggs and ‘that hens’ eggs are generally laid by hens’. But this is a chair I’m sitting in, and it’s black, and it’s made of oak. And this is a hen, and this is a hen’s egg. These are all facts I know, and they are, patently, non-structural—and more than merely spatiotemporal—facts about the nature of reality.’

My reply to this objection is similar to Moore’s a hundred years ago in his disquisition on hens and their eggs. I take it that there are many truths that we know about hens and chairs and other things. But I also take it that hens are wholly made of the fundamental material constituents that physics discusses, and that the crucial sense, expounded above, in which it is true to say that we know nothing about the non-structural non-spatiotemporal nature of matter is entirely compatible with the sense in which we know that there are hens, and what hens are, and what wood is, and so on.

‘But we also know about the fundamental material constituents you mention. We know what hens are made of—carbon, hydrogen, and oxygen, mostly—and we know what carbon, hydrogen, and oxygen are: we know that they in turn are made of electrons and and quarks (or fermions on a bed of bosons) with various characteristics. And in knowing this we once again know non-structural facts about the nature of reality.’

Well, I agree that we should allow a very robust sense in which we just do know what black is, and oak, and so on, but there doesn’t seem to be an equally robust sense in which we know what electrons and spin and charge are, in such a way that our knowledge of them amounts to non-structural and more than spatiotemporal knowledge of the nature of reality. In taking us down into the particle basement in this way, you have re-expressed my claim that the sense in which we know that there are chairs, and what they are made of, is compatible with the sense in which we know nothing about the non-structural and non-spatiotemporal nature of the physical.

The second answer allows for the sake of argument that we can treat electrons and quarks like tables and chairs, and say that we have non-structural and more than spatiotemporal knowledge of their nature, but point simply rearises. I take it that leptons and hadrons have some intrinsic non-structural nature in virtue of which they enter into the numerically or mathematically expressible structural relations they do enter into. The sense in which we know nothing about their intrinsic non-structural nature is entirely compatible with the sense in which we know what electrons are, which I take to be akin to the sense in which we know what hens are.

‘Good. Now we’ve reached the bottom issue, and I can see what your mistake is.

10 True materialism

I have suggested that our general theoretical conception of the mental has substantial non-structural descriptive content, because we have acquaintance with fundamental features of the mental nature of reality just in having experience in the way we do. Our general theoretical conception of the non-mental has substantial structure-specifying content, and I have suggested, with some hesitation, that it may also have crucial and correct non-structural content deriving from spatiotemporal concepts. Apart from this, though, it is arguable that we know nothing about the intrinsic or non-structural nature of non-mental reality - assuming that there is such a thing.

With this in place, we may ask what is is to be a genuine materialist. The first thing to do is to intone once more that realistic materialism entails full acknowledgement of the reality of Experiential phenomena: they are as real as rocks, hence wholly physical, strictly on a par with the phenomena of extension and electricity as characterized by physics. They are part of fundamental reality, whatever is or is not the case.

It follows that current physics, considered as a general account of the general nature of the physical, is like Hamlet without the prince (or at least like Othello without Desdemona): it contains only predicates for non-Experiential being, so it cannot characterize Experiential being at all (recall the definition in §2). It cannot characterize a fundamental feature of reality at all.

No one who doubts this is a true materialist. Partly for this reason, I think that genuine, reflective endorsement of materialism is a considerable achievement for anyone who has had a standard modern Western education. Materialism must at first provoke a feeling of deep bewilderment in anyone contemplating the question "What is the nature of the physical?" The occurrence of such a feeling is diagnostic of real engagement with the materialist hypothesis, and hence with the thought that Experiential phenomena are physical phenomena, just like extension phenomena and electrical phenomena as characterized by physics. Russell is profoundly right when he says that materialists "have been guilty, unconsciously and in spite of explicit disavowals, of a confusion in their imaginative picture of matter". I think that some will be unable to shake off the confusion, although Locke made the crucial move long ago. They may think that modern science has changed the situation since then. It has - but only in so far as it has massively reinforced Locke’s point.

Perhaps I am generalizing illegitimately from my own experience, revealing my own inadequacy rather than the inadequacy of recent discussion of the "mind-body" problem. I don’t think so. Materialism requires concerted meditative effort. Russell recommends "long reflection". If one hasn’t felt a kind of vertigo of astonishment, when facing the thought, obligatory for all materialists, that consciousness is a wholly physical phenomenon in every respect, including every Experiential respect - a sense of having been precipitated into a completely new confrontation with the utter strangeness of the physical (the real) relative to all existing common-sense and scientific conceptions of it - , then one hasn’t begun to be a thoughtful materialist. One hasn’t got to the starting line.

Some may find that this feeling recurs each time they concentrate on the mind-body problem. Others may increasingly think themselves - quietistically, apophatically, pragmatically, intuitively - into the unknownness of the (non-mental) physical in such a way that they no longer experience the fact that mental and non-mental phenomena are equally physical as involving any clash. At this point "methodological naturalism" - the methodological attitude to scientific enquiry into the phenomena of mind recommended by Chomsky - will become natural for them, as well as correct. I think it is creeping over me. But recidivism is to be expected: the powerfully open state of mind required by true materialism is hard to achieve as a natural attitude to the world. It involves a profound reseating of one’s intuitive theoretical understanding of things.

I say "intuitive theoretical understanding", but it isn’t as if there is any other kind, when the stress falls on the word "understanding". For (briefly) what we think of as real understanding of a natural phenomenon is at bottom a feeling, and it is always and necessarily relative to other things one just takes for granted, finds intuitive, feels comfortable with. This is true in science as it is in common life. I feel I fully understand why this tower casts this shadow in this sunlight, given what I take for granted about the world (I simply do not ask why light should do that, of all things, when it hits stone). I may also feel I understand - see - why this billiard ball does this when struck in this way by that billiard ball A. But in this case there is already a more accessible sense in which I don’t really understand what is going on, and it is an old point that if I were to ask for and receive an explanation, in terms of impact and energy transfer this would inevitably invite a further question, starting a series of questions and answers that would have to end with a reply that was not an explanation but rather had the form "Well, that’s just the way things are".

The true materialist outlook may become natural for some, then, but many will find they can maintain it only for relatively short periods of time. It is not a small thing. To achieve it is to have evacuated one’s natural and gripping common-sensescience-based conception of the nature of the physical of every element that makes it seem especially puzzling that Experiential phenomena are physical. I think it is to be at ease with the idea that consciousness is a form of matter.

It can help to perform special acts of concentration - focusing one’s thought on one’s brain and trying to hold fully in mind the idea that one’s experience as one does so is part of the physical being of the brain (part of the physical being of the brain that one may be said to be acquainted with as it is in itself, at least in part, because its being as it is for one as one has it just is what it is in itself, at least in part). It is worth trying to sustain this - it is part of doing philosophy - , forcing one’s thought back to the confrontation when it slips. At first one may simply encounter the curious phenomenological character of the act of concentration, but it is useful to go on - to engage, for example, in silent, understanding-engaging subvocalizations of such thoughts as "I am now thinking about my brain, and am thinking that this experience I am now having of this very thinking - and this subvocalization - is part of the physical activity and being of my brain." It is also useful to look at others, including young children, as they experience the world, and to think of the being-in-time of the common-or-garden matter that is in their heads (hydrogen, oxygen, carbon, iron, potassium, sodium, and so on). It is useful to listen to music, and focus on the thought that one’s auditory experience is a form of matter.

11 Knowledge of ignorance

Finding it deeply puzzling how something could be physical is not the same as finding something that one takes to be physical deeply puzzling. It is often said that quantum theory is deeply counterintuitive - e.g. in its description of the wave-like and particle-like behaviour of fundamental particles, but no one seems to find it puzzling to suppose that it deals wholly with physical phenomena.

The main reason for this seems to be as follows: WAVE and PARTICLE engage smoothly with standard physics concepts of shape, size, position, motion, and so on. There is, so far, a clear sense in which the two concepts are theoretically homogeneous, or at least non-heterogeneous; they operate on the same, single conceptual playing field of physics. But when we try to integrate conscious-experience terms with the terms of physics (and common-sense physics), we find that they entirely lack any such felt theoretical homogeneity, or non-heterogeneity. To this extent, they force constantly renewed bewilderment - in a way quite different from the way in which quantum-mechanical phenomena do - on materialists who like to think they have some sort of coherent, theoretically unified understanding of the overall nature of the physical, however general that understanding may be, and however incomplete in its details.

But this is the central mistake: to think that one has some sort of theoretically unified understanding of the overall nature of the physical. Once one realizes that this cannot be true, if materialism is true, things change. It begins to look as if there is actually less difficulty in the suggestion that physical phenomena have both Experiential and non-Experiential being than in the suggestion that photons (e.g.) behave both like particles and waves. For in the case of Experiential terms and non-Experiential terms there is no direct clash of concepts of the sort that occurs in the case of the wave-particle duality. Being a wave is incompatible with being a particle, but there is nothing in the possession of non-Experiential being that we know to be intrinsically inimical to the possession of Experiential being: we simply do not know enough about the nature of the non-Experiential to have any good reason to suppose that this might be so. Thus the Experiential and the non-Experiential terms do not in fact actively clash, as the wave and particle terms do. Rather, they fail to connect or engage. One is making progress as a materialist when one has lost all sense of an active clash. It has no scientific justification. As Russell says, "the physical [sc non-mental] world is only known as regards certain abstract features of its space-time structure - features which, because of their abstractness, do not suffice to show whether the physical world is, or is not, different in intrinsic character from the world of mind".

Arnauld made the essential point in 1641, in his comments on Descartes’s Meditations, and he was not the first. Locke in 1690 "did not apprehend that there was any real inconsistency between the known properties of body, and those that have generally been referred to mind", as Priestley observed. Hume in 1739 shows a very clear understanding of the point. Priestley in 1777 argues, with unanswerable force, and by appeal to a scientific conception of the physical that (in essence) still holds good today, "that we have no reason to suppose that there are in man two substances so distinct from each other as have been represented". Kant concurs in 1781, although his special terms of debate preclude him from agreeing directly with Priestley’s further materialist claim that "mind . . . is not a substance distinct from the body, but the result of corporeal organization"; that "in man [thought] is a property of the nervous system, or rather of the brain"; that "sensation and thought do necessarily result from the organization of the brain". The quality of the mind-body debate is in many ways lower today than any other time in the last three hundred years.

Substance dualism may have looked like a plausible response to the mind-body problem in Descartes’s time, for strict classical mechanistic materialism, according to which the physical world consists entirely of small, solid, intrinsically inert particles in motion, was then the dominant view, and Leibniz’s image of the mill seemed attractive. But the strict mechanist understanding of the physical world was fatally undermined by 1687, when Newton published his Principia. Since then we have had no good scientific reason to think that mind is not physical. And even before Newton, in the high days of "contact mechanics", there were no philosophically respectable grounds for claiming that mind is not physical. The mechanists or "Cartesians", as Hume calls them, made a wholly unjustifiable move: they "established it as a principle that we are perfectly acquainted with the essence of matter". That is, they not only assumed that their fundamental theory of matter was sound as far as it went; they also assumed that it went all the way - that it was complete. It is the second of these two false assumptions that causes most trouble, for even if the Cartesians had been right that all physical change is a matter of the motion, contact, and impact of solid particles, they still would not have been justified in claiming that this fact was definitely - knowably - incompatible with some of it also being a matter of conscious goings on. Many today make exactly the same sort of mistake.

12 The reality of appearance

I have claimed that thoughtful materialism requires draining one’s conception of the non-Experiential physical of any element that, in a generally puzzling world, makes it seem especially puzzling that the Experiential is physical. But some philosophers think this is the wrong way round: they think we have to drain our conception of the Experiential of any element that produces special puzzlement, leaving our existing conception of the non-Experiential physical in place. But no substantial draining can be done on the Experiential side. In having Experience in the way we do, we are directly acquainted with certain features of the ultimate nature of reality, as Russell and others have remarked - whether or not we can put what we know into words in any theoretically tractable way. This is so whatever it is best to say about any non-Experiential (e.g. dispositional) aspects of the mental that there may be. We may hope to develop our understanding of the nature of the Experiential, but we can do this only by adding to what we already know of it by direct acquaintance.

"But in having experience we only have access to an appearance of how things are and are not cognizant, in the mere having of the experience, of how anything is in itself."

The reply is immediate. Here, how things appear or seem is how they really are: the reality that is at present in question just is the appearing or seeming. In the case of any Experiential episode E there may be something X of which it is true to say that in undergoing E we only have access to an appearance of X, and not to how X is in itself. But serious materialists must hold that E itself, the event of being-appeared-to, with all the qualitative character that it has, is itself part of physical reality. They cannot say that it too is just an appearance, and not part of how things are, on pain of infinite regress. They must grant that it is itself a reality, and a reality with which we must, in plausibility, be allowed to have some sort of direct acquaintance. As Russell says, we must "treat ‘seeming’ with respect".

At this point some may try to adapt Ryle-type arguments for the "systematic elusiveness of the ‘I’" to the present case. They may argue that anything that can count as knowledge of experience involves an operation of taking experience as an object that necessarily precludes apprehending it in such a way that one can be said to have access to how it is in itself, rather than merely to an appearance of it. I suspect that this form of argument is invalid even in its original application, where it is used to argue that the putative mental subject of experience can never directly apprehend itself. But even if this is not so, it has no valid application to the present case - to things like pain and colour-experience. The way a colour-experience is Experientially, for the subject of experience that has it, is part of its essential nature - its ultimate reality - as a physical phenomenon. When we claim (with Russell) that to have an experience is eo ipso to be acquainted with certain of the intrinsic features of reality, we do not have to suppose that this acquaintance involves standing back from the experience reflectively and examining it by means of a further, distinct experience. It doesn’t. This picture is too cognitivist (or perhaps too German-Idealist). The having is the knowing.

13 The radiance of reality

I have argued that the first thing that one needs to do, when it comes to the mind-body problem, is to study one’s ignorance: one’s ignorance of the non-Experiential. One’s intuitive theoretical attitude to the nature of the non-Experiential needs to evolve until any sense that there is an active clash between Experiential terms and non-Experiential terms has disappeared, leaving only the awareness that they fail to connect in a way that brings a sense of intuitive understanding. This awareness is not merely a matter of book learning.

At this point at least two paths open up for materialists. The first goes deeper into reflection on the nature of understanding in physics. Proceeding down this path, one encounters one’s sense that at least some of the terms of physics (both common-sense and scientific) connect up with one another in a way that justifies a feeling of intuitive understanding of at least some of what goes on in the world. One is then asked to examine (possibly at length) the question of what exactly one supposes this to amount to. Does it really amount to anything very solid? Is it more than a certain kind of feeling one is disposed to get (either innately or as a result of training) when considering some but not other co-occurrences of features in the world? What exactly is its significance?

One probably has to go down this path, as a materialist, returning to the questions raised on p. 00. But I will choose another, which has a sunnier aspect. Here one confronts the deep puzzlement one still feels when one considers Experiential properties and non-Experiential properties and fails to see how they coexist, and, also, one’s persisting feeling that this puzzlement has, in a puzzling world, a special if not unique status.

The question is whether one can do anything about this. I think physics can help us - it has already helped us a great deal - by diluting or undermining features of our natural conception of the physical that make non-Experiential phenomena appear toto coelo different from Experiential phenomena

The basic point is simple, and can be elaborated as follows. At first, perhaps, one takes it that matter is simply solid stuff, uniform, non-particulate: Scandinavian cheese. Then, perhaps, one learns that it is composed of distinct atoms - particles that cohere more or less closely together to make up objects, but that have empty space (to put it simplistically but intelligibly) between them. Then, perhaps, one learns that these atoms are themselves made up of tiny, separate particles, and full of empty space themselves. One learns that a physical object like the earth or a person is almost all empty space. One learns that matter is not at all what one thought.

Now one may accept this while holding on to the idea that matter is at root solid and dense. For this picture retains the idea that there are particles of matter: minuscule grainy bits of ultimate stuff that are in themselves (in Locke’s phrase) "perfectly solid", continuum-dense. And one may say that only these, strictly speaking, are matter: matter as such. But it is more than two hundred years since Priestley (citing Boscovich) observed that there is no positive observational or theoretical reason to suppose that the fundamental constituents of matter have any perfectly solid central part.

In spite of this, a fairly robust conception of truly solid particles survived all the way into pre-1925 quantum mechanics. It suffered its most dramatic blow only in modern (1925 on) quantum mechanics, in which neither the nucleus nor the electrons of an atom are straight-up solid objects, and are much more naturally thought of as fields. It may be said that the basic idea of the grainy particle survives even here, at least in as much as the nucleus and its components are still fairly well localized within a small central region inside the atom (albeit with small "tails" that go out to infinity), and in as much as the probability of finding one of the (far less localized) electrons is significant only within a volume that is normally considered to be the dimensions of the atom. But this commitment to the localization of particles does not in itself amount to any sort of commitment to continuum-dense solidity, but only to fields and repulsive forces that grow stronger without any clear limit when one travels in certain directions (i.e. towards the centre of the field associated with a particle). And whatever is left of the picture of ultimate grainy bits is further etiolated in quantum field theory, in which the notion of the field more fully overrides the picture of grainy particles. In this theory it becomes very hard to treat "bound" systems like atoms at all. As for what I’ve been calling "empy space" - the supposed vacuum - , it is understood to be simply the lowest energy state of fields like the electron, proton, and photon fields. It turns out to be something which "has structure and can get squeezed, and can do work".

It may be said that quantum field theory is complicated and ill-understood, but it may be replied that grainy, inert bits of matter, naively conceived, are already lost to us independently of quantum field theory, given only the fact that matter is a form of energy, and interconvertible with it. This fact is widely known, however little it is understood, and it seems to me that it further, and utterly, confounds any understanding of matter that takes it to be in any obvious way incompatible with consciousness. To put it dramatically: physics thinks of matter considered in its non-Experiential being as a thing of spacetime-located forces, energy, fields, and it can also seem rather natural to conceive of consciousness (i.e. matter apprehended in its Experiential being) as a spacetime-located form or manifestation of energy, as a kind of force, and even, perhaps, as a kind of field. We may still think the two things are deeply heterogeneous, but we have no good reason to believe this. We just don’t know enough about the nature of matter considered in its non-Experiential being; and doubtless there are things we don’t know about matter considered in its Experiential being. Those who think speculations like this are enjoyable but not really serious haven’t really begun on the task of being a materialist; they haven’t understood the strangeness of the physical and the extent of our ignorance. It is a long time since Russell argued that "from the standpoint of philosophy the distinction between physical and mental is superficial and unreal", and it seems that physics can back philosophy on this question. In fact - and it had to come back to this - we really don’t know enough to say that there is any non-mental being. All the appearances of a non-mental world may just be the way that physical phenomena - in themselves entirely mental phenomena - appear to us; the appearance being another mental phenomenon.

Richard Price is consistently outclassed by Priestley, in their Free Discussion of the Doctrine of Materialism (1778), but he gets this point exactly right, remarking that

if . . . it comes out that [Priestley’s] account of matter does not answer to the common ideas of matter, or that it is not solid extension, but something not solid that exists in space, it agrees so far with spirit [or mind].

This is a rather good description of how things have come out, in physics. The account of matter given by current physics does not "answer to the common ideas of matter". It does not take matter to be "solid extension", but rather "something not solid that exists in space". So far, then, it agrees with our understanding of mind or consciousness, although the agreement can only be negative, because we have no grasp of the non-structural nature (if any) of the non-Experiential being of matter, apart (perhaps) from our grasp of its spacetime structure. All we have are equations.

Whatever you think of this proposal, lumpish, inert matter, dense or corpuscled, stuff that seems essentially alien to the phenomenon of consciousness, has given way to fields of energy, essentially active diaphanous process-stuff that - intuitively - seems far less unlike the process of consciousness. When Nagel speaks of the "squishy brain", when McGinn speaks of "brain ‘gook’" and asks how "technicolour phenomenology . . . can . . . arise from soggy grey matter", when the neurophysiologist Susan Greenfield describes the brain as a "sludgy mass", they vividly and usefully express part of the "imaginative . . . confusion" in the ordinary idea of matter. But we can avoid some of the confusion without much difficulty. Physics, in particular, can help. For there is a clear sense in which the best description of the nature of the non-Experiential in non-technical, common-sense terms comes from physics. For what, expressed in common-sense terms, does physics find in the volume of spacetime occupied by a brain? Not a sludgy mass, but an astonishingly (to us) insubstantial-seeming play of energy, an ethereally radiant form involving extraordinary (to us) quantum-mechanical goings on.

It finds, in other words, a physical object; which, thus far examined, is like any other. Examined further, this particular physical object turns out to have a vast further set of remarkable properties: all the sweeping sheets and scudding clouds and trains of intraneuronal and interneuronal electrochemical activity which physics (in conjunction with neurophysiology) apprehends as a further level of extraordinarily complex intensities of movement and (non-Experiential) organization.

All this being so, do we have any good reason to think that we know anything about the non-mental physical (assuming it exists) that licenses surprise - even the very mildest surprise - at the thought that the Experiential is physical? I do not think so.

The point is still negative. It may destroy one common source of puzzlement, but it doesn’t offer any sort of positive account of the relation between the play of energy non-Experientially conceived and the play of energy Experientially apprehended, and some will find it no help at all. Others may insist that it is a positive mistake to think that it is especially helpful, on the grounds that there is in the end no more difficulty in the thought that the existence of matter naively and grossly conceived involves the existence of consciousness than there is in the thought that matter quantum-mechanically conceived does so.

We can grant them their objection for their own consumption (they are likely to be fairly sophisticated philosophers). Many others - not excluding philosophers - are likely to find the negative point useful, and I will conclude this section by relating it to three currently popular issues: eliminativism, the "hard problem", and "zombies".

Eliminativism. Consider any philosopher who has ever been tempted, even momentarily, by the "eliminativist" suggestion that one has to question the reality of the Experiential in some way in order to be a thoroughgoing materialist. It is anextraordinary suggestion (it is considerably more bizarre than Xenocrates’ suggestion that the soul is a self-moving number), and what is most striking about it in the present context is that it constitutes the most perfect demonstration in the history of philosophy of the grip of the very thing that it seeks to reject: dualist thinking. The eliminativists make the same initial mistake as Descartes - the mistake of assuming that they understand more about the nature of the physical than they do - but their subjugation to dualist thinking is much deeper than Descartes: they are so certain that the physical excludes the Experiential that they are prepared to deny the reality of the Experiential in some (admittedly unclear) way - i.e. to make the most ridiculous claim ever made in philosophy - in order to retain the physical.

The "hard problem". It is seriously misleading to talk too freely about "the hard part of the mind-body problem", as if the problem were clearly posed. It is not, as Chomsky has observed. In fact it is not sufficiently well-defined for us to be able to say that it is hard; for although we have a clear and substantial positive fix on the non-structural nature of Experiential reality, we have no substantial positive fix on the non-structural nature of non-Experiential reality, apart, perhaps, from its spatiotemporal characteristics. To this extent we have no good reason to think that the mind-body problem is a harder problem than the problem posed for our understanding by the peculiarities of quantum physics, or indeed - as Chomsky might say - by the phenomenon of motion.

Zombies. It is, finally, a mistake to think that we can know that "zombies" could exist - where zombies are understood to be creatures that have no Experiential properties although they are perfect physical duplicates (PPDs) of Experiencing human beings. The argument that PPD-zombies could exist proceeds from two premisses: [1] it is conceivable that PPD-zombies exist, [2] if something is conceivable, then it is possible. It is plainly valid, and (unlike many) I have no great problem with [2]. The problem is that we can’t know [1] to be true, and have no reason to think it is. To be a (genuine) materialist is, precisely, to hold that it is false, and while materialism cannot be known to be true, it cannot be refuted a priori - as it could be if [1] were established. PHYSICAL is a natural-kind concept, and since we know that there is much that we do not know about the nature of the physical, we cannot claim to know that a Experienceless PPD - a perfect physical duplicate, no less - of a currently Experiencing human being is even conceivable, and could possibly exist. (To be a perfect physical duplicate of an actual human being, a creature would of course have to be governed by the same physical laws.)

14 Realistic monism

In §1 I pointed out that the word "physical", as used by genuine materialists, is coextensive with "real and concrete": to say something is a physical phenomenon is simply to say that it is a real and presumably spatiotemporal phenomenon, not some sort of "abstract entity". But then why bother to use "physical"? Why not simply use "real"? And why bother with "real", given that we are talking about whatever exists, whatever it is? It is redundant. All one strictly needs, to mark the distinctions centrally at issue in the unfortunately named "mind-body problem", are "mental" and "non-mental", "Experiential" and "non-Experiential". One can simply declare oneself to be a Experiential-and-non-Experiential monist: one who registers the indubitable reality of Experiential phenomena and takes it that there are also non-Experiential phenomena.

I have nominated this position for the title "realistic monism", having explicitly assumed (p. 000) that any realistic position must take it that there is non-Experiential being. This assumption can be backed by an argument that seems quite strong - (1) Experience certainly exists, (2) Experience is impossible without a subject of experience, (3) a subject of experience cannot itself be an (entirely) Experiential phenomenon, so (4) the existence of Experience entails the existence of non-Experiential phenomena. But one can have no deep confidence in the correctness of the assumption if one accepts the general principles of ignorance defended in this paper, and the argument invites the reply that although a subject of experience must have non-experiential being relative to its own experience, its non-experiential being may be the experience of some other, lower-order, subject or group of subjects, and so on down. I do not know whether this reply really makes sense, but it seems clear that the assumption must be left as an assumption: one cannot really know what is "realistic", at this point.

"You say we can do without the word ‘physical’. But if one can do without ‘physical’, then ‘materialist’, used so diligently in this paper, is just as superfluous. You have already stated (note 10) that you make no distinction between materialism and physicalism, and the word ‘materialist’ is deeply compromised by its history."

History is two-faced, and I think that "materialist" - an adjective formed from the natural-kind term "matter" - can be harmlessly and even illuminatingly retained. What, after all, is matter? It is whatever we are actually talking about when we talk about concrete reality, if materialism is true, and realistic materialist monists who take it that Experience is wholly material in nature can assert with certainty that there is such a thing as matter, for they can know with certainty that there is such a thing as concrete reality (i.e. Experience, at the very least). What they will want to add to this, as materialists, is the insistence that nothing can count as matter unless it has some sort of non-Experiential being (see §4); together with the working presumption - duly modulated by awareness of the extent of our ignorance - that current physics is genuinely reality-representing in certain ways, even if this is only a matter of the holding of certain relations of structural correspondence. If in fact current physics is completely off-beam, then one might say that their claim to be materialists effectively lapses; but so does everyone else’s.

In so far as I am a realistic materialist monist, then, I presume that physics’s best account of the structure of reality is genuinely reality-representing in substantive ways, and that the term "materialist" is in good order. It has travelled far from some of its past uses, but there is no good reason to think that its meaning is especially tied to its past uses rather than to the current understanding of matter. And there is a sense in which its past use makes it particularly well worth retaining: it makes the claim that the present position is materialist vivid by prompting resistance that turns out to be groundless when the position is properly understood.

So much for "materialist"; what about "monist"? There is serious unclarity in this notion, for monists hold that there is, in spite of all the variety in the world, a fundamental sense in which there is only one basic kind of stuff or being. But questions about how many kinds of stuff or being there are are answerable only relative to a particular point of view or interest; and what point of view is so privileged that it allows one to say that it is an absolute metaphysical fact that there is only one kind stuff or being in reality? Materialists call themselves monists because they think that all things are of one kind - the physical kind. But many of them also hold that there is more than one kind of fundamental particle, and this claim, taken literally, entails that there isn’t after all any one basic kind of being out of which everything is constituted. For it is the claim that these particles are themselves, in their diversity, the ultimate constituents of reality; in which case there is kind-plurality or stuff-plurality right at the bottom of things.

"But these particles are nevertheless all physical, and in that sense of one kind."

But to say that they can be classed together as single-substanced in this way is question-begging until it is backed by a positive theoretical account of why it is correct to say that they are all ultimately (constituted) of one kind (of substance). To claim that their causal interaction sufficiently proves their same-substancehood is to beg the question in another way, on the terms of the classical debate, for classical substance-dualists simply deny that causal interaction entails same-substancehood. The claim that they are all spatiotemporally located also begs the question. For how does this prove same substancehood?

It may be replied that all the particles are just different forms of the same stuff - energy. And it may be added that the so-called fundamental particles - quarks and leptons - are not strictly speaking fundamental, and are in fact all constituted of just one kind of thing: superstrings. And these monist approaches deserve investigation - to be conducted with an appropriately respectful attitude to panpsychism. But one can overleap them by simply rejecting the terms of the classical debate: one can take causal interaction to be a sufficient condition of same-substancehood.

I think that this is the right dialectical move in the present context, if one wants to retain any version of the terminology of substance. Dualists who postulate two distinct substances while holding that they interact causally not only face the old problem of how to give an honest account of this interaction. They also face the (far more difficult) problem of justifying the claim that there are two substances. As far as I can see, the only justification that has ever been attempted has consisted in an appeal to the intuition that the mental or the Experiential is utterly different in nature from matter. But this intuition lacks any remotely respectable theoretical support, if the argument of this paper is even roughly right. The truth is that dualism has nothing in its favour - to think that it has does is simply to reveal that one thinks one knows more than one does - and it has Occam’s razor (that blunt sharp instrument) against it. It may be that substance dualism - or pluralism - is in fact the best view to take about our universe for reasons of which we know nothing. So be it: the objection to dualism just given remains decisive when dualism is considered specifically as a theoretical response to the "mind-body problem".

"But why persist with ‘monist’? You might as well call yourself a ‘neutral pluralist’, for all the difference it makes, and ‘monist’ carries bad baggage. Why not simply call yourself a ‘non-committal naturalist’, or, with Chomsky, a ‘methodological naturalist’? Or a ‘?-ist’?"

This section stirs up large questions. I could indeed call myself an Experiential-and-non-Experiential ?-ist. For the moment, though, the physics idea (the ancient idea) that everything is made of the same ultimate stuff - that the deep diversity of the universe is a matter of different states or arrangements of the same fundamental ens or entia - that "in the whole universe there is only one substance differently modified" - seems to me as compelling as it is remarkable, and I choose to register my attraction to it with the word "monism". If realistic monism is Chomskyan methodological naturalism ontologized, good.

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