Return of the Zombie

Please see my previous post for a little background on the urgent philosophical question of whether zombies can beat zoombies and shombies in a ping pong match. At least we know that they can all beat Sarah Palin in a debate.

I readily acknowledge both my tardiness and my wordiness (the two not being unrelated) in replying to Richard Brown. The world, or at least my path through it, is unfortunately so configured that blogging often has to take a back seat to things that I consider mundane and relatively dull. Oh well. The present issue came to life when Richard, on his blog, offered some ideas about creatures (zoombies) that are complete non-physical duplicates of normal law-abiding citizens like you and me, but fail to be conscious; and those that are physical duplicates, have no non-physical properties, and yet are conscious (shombies). Both of these beings are conceivable, according to Richard, or at least as conceivable as zombies, which are physical duplicates of ourselves that lack consciousness. The conceivability of zombies is supposed to support the argument that physicalism is wrong, because if we can conceive of a creature exactly like us but not conscious, it follows from this that it is not logically necessary that physical systems like ours must be conscious; and from this it follows that we cannot reduce consciousness to some equivalent physical description. So if zombies are conceivable, materialism is wrong. But according to Richard, the conceivability of his two new creatures equally suggest that dualism is wrong. And according to me, the proliferation of these things suggests that we had all better run.

Richard eventually put his thoughts into a form appropriate to the hallowed environment of a philosophy conference (that of the Long Island Philosophical Society), and I responded in similarly civilized fashion. And now that we've got that over with we can proceed to thrash about and flame each other on the Internet. (Just kidding - I think.) I will take up as many of Richard's responses to my reply as I can, while conceding in advance that he will probably outlast me (if not outwit me) in any blog debate. And given that Brown is the name he chose for his online identity I shall now revert to that appelation, while wondering aloud how a name like "one more Brown" gets to be a rigid designator.

Brown's response to my critique begins with my defense of the idea that zombies are indeed conceivable. I suggested that I can imagine a being that is physically identical to me but unaware of the blue tint of the light in the room, and I can expand on that concept to conceive of a zombie (who is unaware of not only the bluish tint but everything else). Brown's response is:

"What we need is to imagine me being in the very same brain state and not being conscious of the blueish tint. This is exactly what is in question –that is, whether this is something that can be imagined– and so this is at best question begging."

David Chalmers, you will recall, was said to be begging questions by ruling out the possibility that "mind" is just a popular term for a physical system; if so, according to Brown, the nonexistence of zombies is a necessary truth and zombies are therefore unimaginable. Now I am allegedly begging questions by assuming that I can imagine being in the same brain state whether aware or unaware of a bluish tint. But I think this is a misuse of the term "question-begging". Brown seems to think the (hidden) form of the argument is,

1. Let's assume physicalism is wrong.
2. If physicalism is wrong, then I can imagine that we have physical duplicates that are not mental duplicates.
3. If I can imagine that we have physical duplicates that are not mental duplicates then the mental does not logically supervene on the physical.
4. Therefore physicalism is wrong.

But the second premise does not depend on the assumption that physicalism is wrong. It is an appeal to intuition, pure and simple. According to Brown, Kripkean semantics prohibit the assumption that this intuition is possible until we have first checked to see if physicalism might be correct. I am actually tempted to hand him this point because it would be the proverbial pyrrhic victory. For if I give him that, he equally has to give me the point that he cannot assume that zombies are not conceivable until we have already established what we are currently attempting to discuss. And with this stalemate at hand, we can proceed to lose our ticket to any intelligent discussion of issues which might eventually be decided by some empirical discovery. So it will be question-begging, for example, to say that the following worlds are conceivable: that in which there is no being to whom gave Moses the ten commandments; the one where large manlike creature called 'bigfoot' are nothing but a hoax; and the imaginary space in which Loch Ness is devoid of living creatures larger than a lake trout. These are question-begging in roughly the same sense that it is "question-begging" to say that a world in which there is no physicalist reduction of consciousness is conceivable, and thus that I can conceive of a world in which there is a being physically identical to myself but lacking consciousness. In all these cases, it may, as far as science is concerned, turn out that these names or definite descriptions ("god", "bigfoot", "Loch Ness monster" and "the physical facts that constitute consciousness") identify actual entities, and if we allow that, we cannot say we conceive of the worlds in question.

If this isn't a spurious argument I'll eat my copy of Naming and Necessity. Does Kripke say that we can't conceive of the mind as non-physical? Quite the opposite. Does Putnam say I can't conceive of water as XYZ? Quite the opposite. Here's Putnam: "My concept of an elm tree is exactly the same as my concept of a beech tree... (This shows that the identifcation of meaning 'in the sense of intension' with concept cannot be correct...)" (Mind, Language and Reality, Phil. Papers V.2, p.226) What's the point? I can conceive of things that are necessarily false, e.g., "Beeches are just like elms". Not "I believe [falsely] that I can conceive of a world in which beeches are just like elms" but I conceive of such a world, plain and simple. (Or I imagine it if you like, but conceiving does not have to include mental imagery.)

Brown should get off this begging-the-question kick. Nothing about what I can or can't conceive today depends on what science discovers tomorrow. If I can't conceive of zombies once I have studied the physical reduction of consciousness (which has been added to Psych 101 texts in the year 2525) then fine, I can't do it. But to bring in a posteriori necessity to show that I can't conceive today what might turn out to be false tomorrow is really cuckoo, a curious technical trick at best. If that were really the implication of the theory, it would be a reductio of Kripkean semantics. But that is not what the theory implies.

There is another problem with Brown's methodology, which is captured in his statement that "This is exactly what is in question –that is, whether this is something that can be imagined." Look, an artist covers a canvas in black paint and says, "This depicts a zombie". You are confused, no doubt, but what exactly can you say? "How? Why can't I see the zombie's shape? Is there anything else in the picture? Were you on drugs when you painted it?" These might be legitimate questions; what is not legitimate is to say, "No it isn't; I'm looking right at it and there is no zombie there." Does the artist even need to reply to this? She can laugh, because the statement is nonsense in this context; or she can say, "When you learn to see the world the way an artist sees it, you will perhaps see a zombie there; and if you don't, I can't help you." (In Goodman's terms, not every picture that represents a zombie is a zombie-picture.) The same holds true for mental pictures, conceptions, imaginings, etc. I know what a zombie is, I am not a hallucinating schizophrenic, I am an honest guy and I believe I am conceiving of a zombie. So I am conceiving of a zombie. Once the basic psychosocial background is given, my claim goes through automatically. It's not corrigible. It doesn't depend on facts or on Kripke. And it especially does not depend on some inspection (per impossible) of my conception to compare it in fine detail with the putative physical correlate that will be discovered some time hence. The details of a conception are stipulated, not set in place like clockwork. Otherwise it has to be said that I cannot really conceive of an automobile, since I haven't the foggiest idea what goes on inside a transmission (though I doubt it is little men turning cranks).

Last point, which came up in a discussion session at the conference: the point of the zombie argument is to deny the claim on logical supervenience, the idea that the mental logically supervenes on the physical. "Logical" here is the same as conceptual; the point is to show that the mental is not conceptually identical to some physical substratum (see Chalmers, p,35). Brown, as far as I can tell, seems to think "logical supervience" is just materialism, but I doubt that. The target is not the brand of materialism that says that once the physical facts are known, the facts about consciousness can be scientifically deduced; the target is the brand that says that once the physical facts are known, the facts about concsiousness are logically entailed; they simply fall out of a correct description of the brain. As Kripke says, a consistent materialist would have to hold that a complete physical description of the world is a complete description tout court; once we have it, it should just be obvious where consciousness lies in it, though it might not be called by that name. That is a logical supervenience position, and it is quite different from physicalism in general. Chalmers and I are both physicalists of a sort; we think that at some level, in the world as it is, consciousness is dependent on brain chemistry and structure. The zombie argument is not directed against this belief, and would not be effective against it. It is meant to show that we need not believe that consciousness is going to just "be there" when we announce the result of the ultimate brain scan. Scan all you want; at the end of the day you will still have to have some other kind of explanation for consciousness. The situation is (not coincidentally) somewhat like Kripke's view of rule-following: state every empirical fact you can find about the system, you will not find the rule there. Nor consciousness, if you proceed in that manner. So there is no entailment of consciousness by physical facts, and that is what logical supervenience is, and what the zombie argument is meant to cast doubt on.

The next point in Brown's response refers to my comment that in cases of aspect-change no physical difference takes place, although a mental difference does:

Alterman goes one to cite, as evidence, his convixtion (sic) that he has no reason tot hink that there is a microphysical change in his brain when he is looking at an ambiguous stimulus (like the duck-rabbit, or the Necker cube), but this is rather naive. There is evidence in both Humans and primates that there are changes in brain activation that correlate to the change in perception in these kinds of cases.

Let's keep in mind what we are talking about here. I used the duck-rabbit example to support the point that we can conceive of a zombie by enlarging on the intuitive idea that changes in mental state can occur without a change in the physical description of the system. When I observe the duck and then notice the rabbit it seems that no change takes place in the physical description of the system. Brown is arguing that this is an illusion, for brain scans show some "brain activation that correlate to the change in perception". I think there is less here than meets the eye. It stands to reason that some stimulation occurs when anything like perception, recognition, concentration, etc. takes place. Nobody disputes that, so it can't be the issue. The issue is whether it is conceivable that a being physically identical to myself could exist without conscious activity. And since it is certainly conceivable that no change takes place when I switch from one to the other, it is by enlargement conceivable that some being never undergoes such changes.

But I am not inclined to leave it at that. For the "change" that Brown points to is nothing more than an indication of an increase in blood flow (or possibly electrical activity) to some area involved with perception. (Roughly the same areas are often involved in both external perception and recognition of mental images.) So what does that show? It certainly is a long way from suggesting that some brain activity is identical with the percept "there's a rabbit in this picture"! In fact, though I do not know which particular bit of research Richard has in mind, I would be willing to bet him lunch that it shows only that the act of searching in the picture for the new image (like the achievement of stereoscopic vision, to take another example) involves some brain activity; no way it can show that there is any difference in the organism while it perceives a duck vs. a rabbit.

But I am even willing to grant that such a difference might be found; for example, it might be shown that certan vectors activated in one case have a historical (causal) relation to vectors activated in the perception of actual ducks, and the other in the perception of actual rabbits (or of realistic duck or rabbit pictures - it doesn't really matter which). So let it be the case that for every individual, nerve cell activation occurs in the duck-rabbit picture specifically in relation to the history for that individual of previous perceptions of the appropriate form. Unfortunately, the physicalist is still in need of an identity much stronger than this. The burden on the physicalist is to give a brain specification that just is the cognition of rabbit-shape (or blue-tintedness) or a strong reason why it is likely that such a specification will be found. The burden on the anti-physicalist is just to give an intuitive reason why that is unlikely to happen. Which I did, but I am more than willing to go a step further, and put it like this: there is no reason to think anyone will ever find a neurological specification that is, so to speak, the transcendental condition guaranteeing the truth of the utterance "he sees a rabbit-picture" or "he sees a duck-picture". And if that won't happen, the fact that some blood flows to the area that manages changes in perception is of little interest.

Brown next takes on another example I used to demonstrate the conceivability of zombies, that of sleepwalkers and blindsight. These people, he insists, are in states "which obviously include a physical difference" from ordinary conscious states. Once again, that is not really relevant to the point of the example. We are talking about conceivability; the example is meant to bolster the plausibility of the claim that zombies are conceivable (to provide "evidence" for conceivability, in the only intelligible sense of Brown's demand for it), and if it does that, it has the effect it is intended to have. It is in no way intended to show that people in such states are in physically identical brain states to non-sleeping, non-brain-damaged individuals who might perform the same actions. To show that might be sufficient to prove the conceivability of zombies, but it is far from necessary. I don't think I need to belabor this any more.

I will have to skip over Brown's next few responses because I think they amount to sticking by the line that Kripkean semantics require us to not assume zombies are conceivable just because we think we can conceive them, and I have already responded to this in sufficient detail. So I move on to his response to what he calls my "stunning claim" that no theory of consciousness has even begun to offer a reductive program for phenomenal experience, such as color vision. Actually I was under the impression that no one would find this even interesting, much less "stunning", because it seems that even materialists have practically written off the effort, generally claiming that qualia are mere illusion and beneath the dignity of a physical theory to explain, while anti-materialists have been saying it consistently since Nagel (whose seminal article is almost entirely an exposition of this very point). So what is Brown's answer to my "stunning claim"? HOT! Yes, of all things, he points to David Rosenthal's (or someone's, in any case) "higher-order thought" theory of consciousness as a program for the physicalist reduction of phenomenal consciousness! Talk about stunning - I thought the very reason that HOT has not attracted many followers is precisely that it offers no hope of explaining phenomenal consciousness. But maybe Brown has been having private sessions with POMAL types who think otherwise.

So what is the response of HOT to my request for "a program for explaining conscious experience, or even the function of consciousness, as an outcome of... biophysical research"? According to Rosenthal, at least, a conscious thought has a qualitative character because the HOT that accompanies it is in some quality-space. That not being very enlightening (even compared with the outright abandonment of attempts to deal with qualia in more hardnosed materialist theories like those of Churchland, Dennett, or Crick) Rosenthal goes on to explain why the HOT has the qualitative it has: it tracks the "similarities and difference" in perceptual space. That's it, the putative program in a nutshell. As for the function of consciousness, Rosenthal's view is that it doesn't really have one; we could get along quite well without it. (Apparently Rosenthal can conceive of zombies; indeed, one could interpret what he says about the function of consciousness to suggest that it is no more than an evolutionary accident that we are not zombies.) In spite of a great deal more verbiage (see Rosenthal's "Sensory Qualities, Consciousness and Perception" in his book, Consciousness and Mind) there is not a whole lot more to this response to what I said was missing.

As Brown characterizes the HOT view of why red objects appear red and not green,

"they do so because we are conscious of ourselves as seeing red not green. You may not like this answer but it certainly does what Alterman says we we don’t have a clue about doing."

Actually, it is not so match a matter of whether one likes the answer as whether one finds it to be an "answer" to anything. It seems to me that this is as far from materialist dreams of a perfect theory as one is going to get. In spite of Rosenthal's often expressed sympathy for materialist analyses of non-conscious thoughts, what he is doing is, broadly speaking, traditional philosophy of mind and language. He offers something like a conceptual analysis of conscious awareness, and gives a defense of it in terms of performance conditions and other standard POMAL ideas. Quite a distance from anything that is going on in the reductive programs that comprise the materialist discourse. I stand by my "stunning claim" - there ain't nothin' happening, in any branch of philosophy or cognitive science, that begins to shed light on how or why we experience reality largely as a succession of qualitative states.

Brown states that he never questioned that conceivability entails possibility, as I said he did in my response. But he presents the main line on which his paper is based, the Kripkean semantics of natural kinds, as being "the typical argument that conceivability doesn't entail possibility". I grant that he never explicitly says that he agrees with this use of Kripkean semantics; he employs it in another way, to question whether zombies are conceivable. On the other hand, he never disputes the first use; indeed he says a number of things which suggest it, e.g., "it cannot be the case that intuitions about zombies are evidence for or against any theory of consciousness". I was reading this as implying that we could grant the possibility of zombies without the dualist gaining any ground. But I am happy to let Brown be the final arbiter of his own intentions, and leave that portion of my reply as a side-issue directed to those who use the Kripke line in the first way. (It does strike me as ironic that there would be two separate arguments against dualism based on a theory of Kripke's which he employs against materialism, but never mind. Since I don't agree with much that Kripke says about Wittgenstein I am not going to appeal to his authority in this case.)

Brown's next point is that Chalmers, contrary to me, is indeed "claiming that there is a necessary link between our non-physical qualities and consciousness". I am not going to go through Chalmers' book to verify that this claim is never made, but it seems to me that the basis for Richard's statement is once again the Kripkean view that if "water" refers to H2O in this world, it does so in all worlds; so if "consciousness" refers to a non-physical property in this world, it does so in all worlds, and its non-physicality is therefore a necessary truth. There are various ways of responding to this. The simplest is to say that Chalmers' argument only leads to the point that it could be a necessary truth that consciousness is a non-physical property. Another is that Chalmers simply does not think that consciousness is a non-physical property in every possible world; he thinks that it is contingently non-physical in this world. A more technical response would involve Chalmers' two-dimensional semantics and the "primary" versus "secondary" intensions of natural kind terms, but I can tell from Brown's latest post that this is only going to lead to a brand new debate. I would rather just refer readers to parenthetical remark which constitutes the last paragraph of p.59 in Chapter 2 of The Conscious Mind, which to my mind offers an adequate reply to the basic premise of Richard's paper. (The reason it is adequate is because it spells out in the technical terms of two-dimensional semantics what I have been saying in more straightforward language throughout my comments: that it simply cannot be the case that we can't conceive of certain possibilities until someone has determined whether some empirical fact about the actual world is true.)

A not terribly important side-issue regarding Brown's view is whether it makes any sense to postulate beings that are similar to me with respect to "all non-physical qualities", or beings that are "completely physical" and are conscious. Suffice it to say that I cannot find a way to allow either of these examples without thinking that the answer to whether physicalism is correct is already built in to the description. Brown seems to think that that doesn't matter, because it is just parallel to what the zombie theorist does. But I think it is not parallel, because the zombie example makes no theoretical assumptions and simply depends on intuition, while Brown's claim that it is question-begging is theory-driven, and the theory is used in a counterintuitive way that most of the disputants do not agree with.

At the end of his remarks, Brown says that he can live with the limited goal I attribute to the zombie argument, that of establishing that there is no conceptual link between physics and consciousness. Hmmmm, I thought that that was what the whole debate was about. Chalmers himself believes that consciousness physically supervenes on brain states, and only argues that it is not the case in all logically possible worlds that this is so. In his book, he presents not only the zombie argument but four other arguments (none of which, I believe, are original, though the presentation is) to the same effect. Why should we be so concerned with this? I am concerned with it because I don't think reductive programs are the way to go. I think a lot will be found out about how consciousness is connected with the biological structures of the brain - 40 Hz waves or whatever - but if the relationship between any particular physical instantiation and consciousness is contingent, we will learn more about consciousness through other methods - perhaps what we might call traditional philosophical analysis, perhaps some of what goes by the name of clinical psychology, perhaps aesthetics. Consciousness, in my view if not in Chalmers', has been most usefully explored in the work of Kant, Wittgenstein, Husserl, James, Freud, Jung, Kohler, and other writers of that nature, as well as in literature of great merit from Homer to Joyce. The whole tradition of cognitive science is at this point nothing but a footnote to those insights at this point. In my opinion, it never will be much more than that as far as this question is concerned.

Zombie, Schmombie - Richard Brown's Efforts to Ressurect Materialism

The indefatigable POMAL blogger and Richard Brown has posted a reply to comments on his Zoombies and Shombies paper, "The Reverse-Zombie Argument Against Dualism" (find a link here), made by a certain "Alderman". Unfortunately, I must object to the egregious act of plagiarism that said Alderman has performed on the comments I sent to Prof. Brown only a few days ago, copying them more or less word for word (how he got hold of them I can only imagine). Should I sue? Actually you can't sue for plagiarism, and I'm not sure what the copyright value of my comments would be, so I have a better solution: Dr. Brown should simply change the "d's" in "Alderman" to "t's" and everything will be alright.

Brown (whose name is quite difficult to misspell, though I tried) certainly outdoes me by a country mile in posting to his blog, an admirable quality that is underrated in the philosophical community. Blogging is I think more in the spirit of philosophy in the Socratic tradition than the institutional control exercised by professional journals and presses. (Anybody who has received the typically biased and ignorant comments on a rejected article from journal reviewers will probably agree wholheartedly with the title of Brown's blog, Philosophy Sucks!) In the future, I will try to do better than the, hmmmm,,, 10 month gap between this and my last post. (Which is a bit less than the gap in my arts blog. Yikes.) In any case, kudos to Dr. Brown for his blogging efforts - not to mention his Cel-ray tonic. (Jeez, names really do get confusing, don't they? Maybe someone should do some philosophical work on this topic.)

What follows is the complete text of my comments on Brown's paper, delivered yesterday (10/18/08) at the conference of the Long Island Philosophical Society. The papers and replies will eventually be published in Calipso, the LIPS online journal, at which point I may remove it from here and put in a link. In the next post I will reply to Brown's replies to my reply to his paper. (And perhaps to some of the replies to his replies to my reply to his reply to Chalmers - which can be found on his blog.)

Zombies, Schmombies... Full Text from the Original Author

The materialist position about consciousness consists in the view that consciousness can be fully explained once we understand the physical materials and processes in the brain. Consciousness will emerge as a supervenient property that can ultimately be reduced to some underlying physical basis. For materialism to go through, it is not sufficient that consciousness be somehow related to or dependent on the brain; it must be nothing more than a brain function, whose supervenience is obscured by some unique aspectual or descriptive stance that stands in the way of our seeing the connection intuitively. In the some versions, such obscurities will eventually disappear, and we will be able to eliminate the introspective illusion of an inner self. Others see the aspectual stance as inherent in the situation. On either view, there is nothing in reality that can either be explained, except as a dependent phenomenon, or do any explaining, other than the physical world.

Most opponents of the materialist view rely heavily on one or more intuition pumps that allegedly bring out a gap between the knowledge and understanding of physical facts and an explanation of consciousness. The "zombie" argument is one such effort. Imagine a creature that has all the physical properties that we would expect a human being to have, and behaves in the ordinary way that human beings would in similar situations, but lacks any hint of consciousness. If this is conceivable (so the argument goes) then physical facts cannot be the logical, or conceptual, foundation of consciousness.

In "The Reverse-Zombie Argument Against Dualism" Richard Brown suggests that the zombie thought experiment provides no compelling evidence that physicalism is wrong. There appear to be at least three tracks to his argument, which I will try to bring out.

The first idea is the contention that zombies, as described by David Chalmers and others, may not actually be conceivable at all. It is easy to miss the logic of Brown's argument here, because at the end he leads us somewhat astray, in my opinion, with suggestions that point in a different direction. One is that proponents of zombieism ought to offer some "evidence" for the conceivability of zombies. A second, related one occurs when Brown says that he himself cannot conceive of a zombie; and again, when he demands "some reason to think that we are really conceiving of a zombie world as opposed to a world that is very similar to ours but not microphysically identical". These points all seem a bit odd, to say the least. Conceptual arguments involve the logic of concepts; any "evidence" for them would surely not be of the empirical sort, and plenty of support has been offered on the conceptual side. The arguments do not depend on the strength of any one person's imagination, but on whether anyone can find a logical contradiction in their use of concepts. And though gross imaginative errors may be to some degree corrigible (I might say I'm imagining a duck but in fact be imagining a chicken), it makes no sense to say that someone who claims to be imagining a microphysical duplicate of me might "really" be imagining something that differs in some small way. (What does "really" really mean here?) But let me try to respond with a defense of the zombie imaginer before we move on to Brown's main argument. My "evidence" will consist in conceptual support for the point that conceiving of a zombie requires nothing more than adding and subtracting properties, something any normal person can do. So first, I can imagine someone physically identical to myself who is in the same room but is not aware of the slightly bluish tint of the late afternoon light, or the background humming of the air conditioning, while I am aware of all that. For I can imagine myself not having been aware of any them, and yet being physically identical to my actual self; just as when I see the duck and then see the rabbit in the same drawing, I have no reason to believe that a microphysical change took place, and even less reason to think that a determinate, repeatable microphysical change took place. Similar arguments could be brought for memory, imagination, and other components of consciousness. Therefore I can imagine a being that is physically identical to myself but lacks consciousness. Second, we can arrive at the concept of a zombie by expanding on concepts like blindsight or sleepwalking. These documented empirical states involve acting and behaving in certain situations like a normal human being but completely lacking awareness of one's behavior or surroundings. A being who is always in such states would be a zombie.

This should suffice for evidence of the conceivability of zombies. It is always possible to submerge one's conceptual abilities by becoming enmeshed in a theory. If one believes that all properties are directly reducible to underlying physical characteristics, it becomes difficult to conceive of anything that is not so reducible. In this way, entities that lacked the Aristotelian notion of substance were inconceivable prior to 18th century empiricism. If someone finds it impossible in theory to separate physical structure from any higher-order property whatsoever, then they might react to the notion of a zombie as "inconceivable" in the sense of "beyond the capabilities of imagination". But imagination tied down by theory is not the relevant power for assessing the viability of zombie conceptions.

The more important aspect of Brown's position does not rely on imaginative prowess. His point is that we ought to grant the physicalist at least the possibility that consciousness is nothing more than a high-level effect of the biophysics of the brain. If we do that, then we grant the possibility that consciousness is a natural kind term for some complex configuration of physical parts and processes. On a Kripkean theory of reference, a natural kind terms refer to a natural kind by means of some property that constitutes its identity. "Water" refers to all and only substances that are actually H2O . Once we know that that is the case, we realize that it is necessarily the case, and that the statement "it's water, alright, but it's not H2O" contains a conceptual confusion. "Consciousness" may similarly refer to whatever the underlying physical basis of consciousness turns out to be. We may not know that identity now, but when we do we will realize that zombies - physical duplicates of ourselves but without consciousness - never really were conceivable in the first place. According to Brown, if we insist that zombies are conceivable, we simply beg the question against this argument.

The question I have about this argument is, who is really begging the question? The logic of Brown's argument is that dualists cannot force the issue against materialism by stating a priori that zombies are conceivable, since it may turn out a posteriori that the connection between brains and consciousness is a necessary one. By the same token, one could have argued in the 19th century that a thought experiment designed to show that light is not a substance but a wave begs the question against the a posteriori necessary truth that light is the propagation of photons. The form of the objection seems wrong, because we cannot say in advance that discovering a physical basis for consciousness will make zombies inconceivable. Consciousness could be more like the terms "evolution" or "radiation" than like "water" or "heat". The former are natural kind terms, but neither has an essence that can be expressed in an identity statement. I fail to see any reason why thought experiments should be constrained by the combined demands of a controversial theory of reference for natural kind terms and the empirical possibility that reductionist programs will be successful. To focus on the latter for a moment, after two centuries of psychophysical experiments we still have no reason to believe that consciousness can be reduced to biophysical properties. As Chalmers carefully explains, none of the popular reduction programs have brought us any closer to bridging consciousness with the physical world. Take our current, fairly sophisticated understanding of color vision; how does it even come close to explaining why red objects appear red and not green? No physicalist story even gets off the ground on this kind of question. The same holds for consciousness in general: in spite of having mapped and experimented with dozens of brain areas, having sophisticated biochemical analyses of brain activity, and even manipulating some basic motor functions with digitally simulated brain signals, we don't have so much as a program for explaining conscious experience, or even the function of consciousness, as an outcome of any of this biophysical research. I think it is quite a leap to say that dualists beg the question by ignoring the possibility that the holy grail of materialism will someday be found.

A second point Brown makes is that conceivability does not entail possibility. The zombie argument depends on the following kind of reasoning. Suppose it were the case that the mental logically supervenes on the physical. Then it would be a metaphysical fact about the universe that whenever you have mind, you have a material foundation. But logical supervenience is an identity relation, so whenever you have the appropriate physical foundation, you must also have mind. Then the concept of a physical foundation without mind ought to be a contradiction of some sort, like the concept of space without distance or consciousness without thought. But the zombie argument is designed to show that this is not the case. Let it be granted, then, that the zombie argument demonstrates the conceivability of zombies. We can conceive of life without death, too, and many other things that may not in fact be physically possible. In the end, then, the zombie argument demonstrates nothing of interest to anyone except philosophers, and the search for a materialist explanation of consciousness can proceed.

I think Brown can reasonably object that while zombies may be metaphysically possible, this kind of conclusion may not establish anything very useful in the debate on consciousness. It establishes that one can be a dualist without violating any rules of metaphysics. But that is an achievement of very limited scope. For no modern dualist wants to be a dualist about substances; we all begin from essentially the same scientific conception of the universe. We believe there is nothing added to biological substrate of consciousness in the sense in which some god or unknown force disperses some ethereal quasi-matter which, combining with our brains, creates consciousness. On the contrary, we all agree that there is no substrate except matter, and the question is how, from matter, you get the qualitative view that is awkwardly expressed by the phrase "what it is like to be" a human, raptor, etc.

But the logical possibility may, on the other hand, be sufficient for what the modern dualist really wants to establish. The point is to argue against the program in which, by assembling enough information about the mechanics of brain processes, and relating that through tomography and other techniques to certain mental phenomena, we will eventually be able to reduce consciousness to brain processes. Someone who believes that there is no matter or force except the ones described by modern physics does not have to purchase that program. They can hold that it is the wrong level of explanation for mental processes. They can believe that mental predicates collect the phenomena that physically supervene on biological entities at too high a level to ever be reduced. They can hold that enormous differences in the underlying structures can accommodate the same mental phenomena, described by the same psychological terms and following the same psychological laws. On this view, the correct kinds of programs for understanding consciousness could be those of William James, Husserl, and Wittgenstein, and not those of Smart, Churchland and Dennett.

I turn finally to the "zoombie" and "shombie" examples Brown offers. As he describes them, a "zoombie" is "a creature which is identical to me in every non-physical respect but which lacks any (non-physical) conscious experience". The idea seems to be that just as my zombie twin is identical to me in every physical respect but lacks qualitative consciousness, my "zoombie" twin is identical to me in every non-physical respect but lacks qualitative consciousness. If the former suggests that consciousness is not a physical property, the latter suggests that it is not a non-physical property.

A "shombie" is "a creature that is microphysically identical to me, has conscious experience, and is completely physical". If shombies are conceivable, then dualists are at best guilty of rejecting the principle of inference to the simplest explanation that accounts for all the known facts. For why should we go about imagining exotic explanations for consciousness when it is perfectly conceivable that physics can explain it all?

According to Brown, these two thought experiments constitute something like a parity of reasoning argument against the zombie argument, and therefore against this particular kind of objection to physicalism. The zombie argument says that it is conceptually possible to disassociate the human body and behavior from conscious experience, and that therefore it is not incumbent on those who hold a naturalistic view of the universe to believe that consciousness is identical to some set of physical processes in the brain. The zoombie argument says that it is conceptually possible to dissociate all non-physical human qualities from conscious experience, and the shombie argument says that it is possible to associate all conscious experience with physical systems like the one in which our minds are embodied. Both thought experiments attempt to show that the zombie argument does not produce any conclusion against physicalism that cannot be produced against dualism by parity of reasoning. So either the zombie argument fails against physicalism, or the zoombie and shombie arguments are equally conclusive against dualism.

I agree that the zombie argument is not a conclusive argument against physicalism; but what it purports to show, at least, is that we are not forced to choose between a materialist theory of consciousness and a spooky view of the universe. If we can conceptually dissociate consciousness from the particular forms in which it is embodied, we can imagine a universe in which it is realized in other ways; and if we can do that, we can give up the idea that there must be a reductive, biophysical explanation of consciousness. I fail to see what parallel objective is achieved by positing "zoombies", since no one is claiming that there is a necessary link between our "non-physical" qualities and consciousness. Brown gives no indication of what he means by such qualities, but it cannot be things like mental or emotional states, because to assume those are non-physical would surely beg the question about consciousness. Perhaps we are talking about relational properties, value-bearing predicates, multiplicity and the like. But we can agree that there is no conceptual link between those properties and consciousness without inventing any new creatures. Since the basis for the sort of property dualism that people like Chalmers propose is not parallel to the metaphysical claims of the materialists, I don't see that this argument has a target.

"Shombies" allegedly show that we can imagine a creature that is "completely physical" having conscious experience. Brown again avoids unpacking the notion of "completely physical", but one thing we cannot say here is that no predicates other than physical ones apply to such creatures, since there is no such thing as an entity to which relational predicates, for instance, do not apply. It appears, then, that the idea of a "shombie" must be roughly that of a machine that has conscious experience. This sort of thought experiment has been tried many times, and I'm not sure what is added by calling it a "shombie". But it does bring out the foolishness of depending on either zombies or robots to prove anything about consciousness. One side says "I can imagine a conscious machine, so consciousness must be reducible to physics"; the other side says "I can imagine a non-conscious twin, so consciousness must not be reducible to physics". Personally I can imagine a talking cloud; am I entitled to the conclusion that we are in cloud-cuckoo land?

Thought experiments, as Wittgenstein pointed out, are not analogous to real experiments, only with thought-materials. They are devices to make us think about what we would say in a very unusual situation; and this can give us insights into how our concepts are organized and how our language works. If we conceive of the mind-body problem along these lines, thought experiments might help us solve it. The zombie idea is therefore somewhat effective in refuting the idea of a conceptual link between matter and mental phenomena; not a small accomplishment in light of the very strong pull that our basic scientific convictions have on our thinking as a whole. But they cannot answer any naturalistic questions, such as whether the notion of conscious experience will eventually fall out of a detailed description of the operation of brain cells. This is a matter for scientific research, and the only reasonable answer we can give right now is that it is far from doing so at this stage of the game. The materialists want to press on because they are convinced there is no other way. The zombie argument suggests that they are wrong about that, but it does not prove that success is conceptually impossible. Brown's thought experiments are helpful is suggesting this corrective to anyone who uses a zombie to scare the materialists away from their research projects.

Anton Alterman

LIPS Conference, St. John's University, Queens, New York, October 18, 2008