I just re-read Karen Bennett’s paper Exclusion, Again. In this paper she argues that causal exclusion arguments provide a nice overall argument for physicalism but do not cut against non-reductive physicalism as usually thought.

Here is how she defines non-reductive physicalism.

Let us begin with the ‘physicalism’ part. It is notoriously hard to define it adequately, but I can at least offer up the same slogans as everyone else. Physicalists not only endorse the completeness of physics, but also think that all the facts are physical facts—that there is nothing ‘over and above’ the physical. Physicalists believe that everything globally supervenes6 on the physical as a matter of metaphysical necessity (see Lewis 1983, Chalmers 1996, and Jackson 1998; see Hawthorne 2002 for interesting challenges to their definitions). That is, physicalists deny that it is merely nomologically impossible for there to be a world physically just like this one but mentally different. There are no special psychophysical laws that link or tether the mental to the physical, and that can be broken.

She is officially neutral on the issue of the a priori entailment of the mental by the physical but she clearly rejects the metaphysical possibility of zombie worlds. So, what, then, is non-reductive about her view?

Nonreductive physicalists do not think—or, at any rate, should not think—that mental events and properties really are not identical to any physical ones. All we think is that they are not identical to any standard physical ones. We have no reason to deny that they are identical to physical events and properties reachable by extension or analogy with standard ones. Let me try to put this marginally more carefully, by loosely distinguishing between a narrow and a broad sense of ‘physical’.

What she means by this seems to be the following. On the one hand we have ‘narrow’ physical properties, events, or objects, which means that they figure in the laws of a ‘clearly physical’ science. So she will count neurons as narrow physical objects because they figure in neuroscience. She will also count electrons and elements, etc. On the other hand there are what she calls ‘broad’ physical properties, events, or objects, which means that we can construct the thing in question out of the narrow properties in some ‘clearly articulated’ way. So,

Broadly physical properties are those constructed from narrowly physical ones by means of property-forming operations like disjunction, conjunction, and quantification (though presumably not negation!). Broadly physical events are those constructed from narrowly physical ones by means of various forms of spatio-temporal, mereological, and modal gerrymandering. And so on. This list is merely supposed to give the general idea, and presumably needs to be expanded and tweaked in various ways.

Given these two notions she formulates non-reductive physicalism as the view that mental states are broadly physical but not narrowly physical. She thus finds it to be a mistake on the part of the non-reductive physicalist to claim that mental properties are not physical at all. They are physical, just not in the narrow sense. There is no neurological state that she will want to say is identical to the mental state, though the mental state is constructed out of those narrow states. So on her view the functional characterization of mental states picks out some narrow physical property as its realizer. When thought of in this way, she continues, non-reductive physicalism has no worries with casual exclusion but dualists do.

The crux of the argument is that if one really wants to maintain a role for the mental in causation you must endorse some kind of over-determination and if that is the case then the following two counterfactuals must be non-vacuously true (which I take to mean; true because the antecedent is true):

(O1) if m had happened without p, e would still have happened and
(O2) if p had happened without m, e would still have happened.

These are supposed to capture our ordinary understanding of overdetermination. Had there been only one of the causes the effect would have been produced by the other cause, and vice versa. The real action is over (O2). She argues that only a physicalist can interpret it in the required way. That is, only the physicalist can say that it is either vacuous or false. A physicalist will think it is vacuously true just in case she thinks that it is impossible that p happen without m. If that is false then (O2) is vacuously true. The dualist has to deny this (zombie worlds are worlds where p happens without m and e happens) and so the dualist cannot say that (O2) can ever be vacuously true. The physicalist can also say that it is false. How? Bennett argues that (O2) is false when we have p ‘out of context’. So, if we replicate the brain state that is pain in the normal brain in some petri dish or if that state were hooked up in some strange/unusual fashion it will be false that e would still come about. The effect depends on the state being in a normally functioning brain in an environment, etc. So in those cases (O2) is false. Bennett then goes on to argue that the dualist cannot take this option. This is because,

doing so would abandoning standard ways of evaluating counterfactuals. For the dualist, the closest world in which the C-fibers fire without pain is not a world in which various surrounding physical facts go differently. It is not a world in which the C-fiber firing takes place in a petri dish, or otherwise without crucial background conditions that actually obtain. It is instead a world in which the psychophysical law linking firing C-fibers in such and such circumstances to pains is violated. It is not a full-blown zombie world, mind you—that would clearly involve the kinds of “big, widespread, diverse violations of law” that Lewis says it is of the first importance to avoid (1979, 47). It is instead simply a world in which just that particular physical occurrence fails to give rise to the sort of mental one that usually accompanies it. That is merely a “small, localized, simple violation of law,” that allows us to “maximize the spatio- temporal region throughout which perfect match of particular fact prevails” (47-48). This one tiny little violation of psychophysical law is a lot easier to accomplish—if it can be accomplished at all—than a big sweeping change in circumstances.

If all of this is right, she concludes, then only the non-reductive physicalist (or the reductive physicist) can avoid the exclusion problem.

But this doesn’t seem right to me. It is wrong to say that the closest possible world where we have p without m is one where there is a small violation of the bridging laws. At least not if one is thinking in terms of the kind of dualism that Dave Chalmers advocates. Since he thinks that consciousness and mental activity are functionally invariant, under normal conditions, he can happily accept that in the cases that Bennett cites (O2) will be false. Sure they do in fact think that there are worlds like the ones that Bennett talks about where the is a local violation of a law and sure Bennett does not really think that there are any such worlds (I tend to agree) but the point is that the worlds that Bennett thinks falsify (O2) are closer to the actual world on both accounts. In those worlds no laws are violated. So the property dualist can say that (O2) is false when you have p without m in the way that Bennett talks about (i.e. p without the general background conditions that let p function normally) but that it is true when you have p without m in the law-violating way. Thus the property dualist can think that (O2) is false in the usual cases, just like the non-reductive physicalist.

Thus if the causal exclusion argument is an argument for physicalism it is an argument for reductive physicalism.

[cross posted at Brains]

The head of the philosophy program at LaGuardia, John Chaffee, is the author of an introductory text book The Philosopher’s Way. The book is entering its fourth edition and John is updating the chapter on the self and consciousness. In particular he is updating the section on Paul Churchland’s eliminative materialism to include a discussion of functionalism. I have been asked to write something that could possibly be included after this discussion and which sums up the the current state of the field, provides a kind of “star map”, and might intrigue an undergraduate to learn more. Tall order! Here is a first draft of what I came up with. Comments and suggestions welcome!
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Contemporary Philosophy of Mind

The philosophical study of the mind in alive and well in the 21st Century. Broadly speaking one might say that there are three over arching concerns in this debate. The first concerns whether consciousness ultimately depends on something computational/functional or whether it depends on something biological. The second concerns whether consciousness is ultimately physical or non-physical, and the third concerns what role empirical results play in philosophical theories of consciousness.

Consider the first question. Some philosophers, like John Searle at U.C. Berkeley and Ned Block at New York University, think that consciousness is distinctly biological. To see what is at issue here we can employ a commonly used thought experiment. Neurons no doubt perform functions. Ask any psychologist or neuroscientist and they will tell you about sodium ions and potassium ions and cell membranes and neurotransmitters, action potentials and the rest. That is, we can think of a neuron as something that takes a certain kind of input (the neurotransmitters from other neurons, ions) and delivers a certain kind of output (an action potential or a graded potential. In principle it seems possible that we could use a nano-machine to mimic a neurons functional profile. This nano-machine would be able to take all of the same input and deliver all of the same output. One might think of it as an artificial neuron in the sense that we have artificial hearts. It is a bit of metal and plastic but it is designed to do the exact same job that the original was meant to do. Suppose now that this nano-machine zaps the neuron and quickly takes its place. Now you have all of your regular neurons and one artificial neuron. But it does everything the original neuron did, so we have no reason to think that this should change you conscious experience overly much. But now we do it with another neuron, and another, and another. The question then, is what happens to consciousness when we replace all of the neurons?

David Chalmers, a philosopher at the Australian National University and New York University, has argued that as a person moves through this process of having their neurons replaced with artificial ones we have a few options. We might say that as their neurons are being replaced their conscious experience is slowly fading like a light on a dimmer switch or we might say that conscious experience was just cut off at some point when some number of neurons were replaced, maybe even the first one! But each of these has a very strange consequence. Suppose that I am having a headache during the hour that my brain is being “fitted” with nanobots. Now suppose that my conscious experience is fading as the process progresses with it being absent at the end. Well, ok, but the first thing to notice is that there can be no difference in your behavior as we go through the process. Each nanobot performs exactly the same function as the neuron, and we can think of the nanobot as instantaneously zapping and replacing the neuron so that you could being driving a car or reading a book while this was happening. But then we end up with the very strange result that we cannot really know that we have conscious experience right now! How do I know that I have a conscious pain? Well, I feel it! But if we were right that it can fade out, or even pop into and out of existence, without me noticing then how do I know it is there in the first place? Chalmers concludes that it is safer to think that the conscious experience would be the same at the end of the process. But if this is right then consciousness depends of functional organization and not on the biology, or non-biology, of the hardware. Those like Searle and Block hold that real neurons with their biological properties are needed in order to have consciousness and that the neural net at the end of the process would no longer be you or have thoughts or pains, but would only simulate those things. Whatever your intuitions are this may not be science fiction for long. Neuroscience is already well along in its investigation of ways to design brain-machine interfaces (for instance as a way of helping amputees with prosthetic limbs that are controlled just like one’s own limbs) and enhancement of the human mind by prosthetic neurology is perhaps not far off.

Notice that in thinking about the question of whether the mind ultimately depends on biological or a functional properties we appealed to a thought experiment. We did not go out and do an actual experiment. We consulted what we intuitively thought about a piece of science fiction. In contemporary philosophy of mind there are those who think that these kinds of intuitions carry great weight and then there are those who think that they do not. Those who think that they carry water think that we can know some deep fact about the nature of consciousness on the basis of reason alone For instance, take Frank Jackson’s Mary thought experiment (Jackson is also a philosopher at the Australian National University). Imagine a brilliant scientist who is locked in a black and white room but who is able to communicate with the outside world via a black and white television screen. Mary is able to learn all of the science that we will ever be able to know. So imagine that she knows the TRUTH about physics, whatever it is. Now suppose that she is released from her room and shown a red ripe tomato. It seems natural to think that she would learn something that she might express by ‘oh, THAT’s what it is like to see red! Everyone out here kept talking about red, but now that I have seen it I know what they mean’. But since she knew all of the physical facts, and yet did not know at least one fact, what it is like for her to see red, it seems like that fact must not be a physical fact. If this and related thought experiments are right then it seems that we do not need empirical evidence of any kind to know that consciousness cannot be physical (note, that David Chalmers talked about above, has advocated this line against physicalism as well. He has introduced philosophical zombies, creatures that are physical duplicates of us but which lack consciousness. If these are possible then consciousness is not a consequence of physics alone).

These arguments, and the knowledge argument of Jackson in particular, have spawned a huge amount of responses. One very natural response is to question the inattention to scientific discoveries. Dan Dennett, a philosopher at Tufts University, argues that this whole strategy is thoroughly misguided. We seem to think that there are these magical conscious properties –the experience of having a pain– that just aren’t there. What is there is the seeming that it is so. Dennett often makes a comparison to magic. Take some professional magician, say David Copperfield. What David Copperfield does is to make it seem as though he has done something else. If you wanted to know how Copperfield performed some trick you would need to explain how he made it the case that it seemed that the statue was gone, or how he made it seem that the person was levitating. You don’t try to show that he really did it but how he made it seem as though he really did. Now is what he does real magic? There is some temptation to say no. Real magic is not just a trick. But sadly, the only magic that is in fact real is the kind that is fake. Dennett thinks the same is true of consciousness. When the functionalist explains what a pain is and someone says that this is not magic enough (Mary wouldn’t know it, or a zombie would lack it), the functionalist should respond that there is no such thing as that kind of magic. What is in fact true is that the brain makes it seem to us as though we have all of this magical stuff going on, but it only seems to be going on. Why think this? Dennett’s main argument is that this has been shown to us by the empirical sciences. Take just one example, the case of so-called change blindness (go online and search for ‘the amazing color changing card trick’ to see a cool example). In these kinds of cases people are presented with a scene where there is a very large central thing that changes. People are usually very bad at spotting the change. Yet when they see the difference they cannot believe that they did not notice it before. That is, from the first-person point of view it really seems as though one has access to a very rich and detailed scene, but actually one is mostly unaware of very large and salient changes in one’s environment. If this is right then our intuitions about science fiction cases may not be that reliable. And this is what Dennett and those like him think.

(cross posted at Brains)

In response to Philip Goff at the OCC David Chalmers has argued that his 2D argument against physicalism is not committed to what Goff called Phenomenal Transparency. PT, to a first approximation, is the claim the having a phenomenal concept allows one to know the true nature of the concept. Opaque concepts do not. Consider the concept of WATER. You can have full mastery of that concept and yet not know that water is H2O. This was the state of everyone prior to the discovery that water was H2O. I have argued that if we take the spirit of the identity theory and transpose it into the 2D framework we get a view that is immune to the zombie argument as this translates into the claim that the primary and secondary intensions for phenomenal concepts come apart. Dave now says that the zombie argument should none the less go through on such a view. It doesn’t depend on phenomenal transparency just like conceiving of Twin Earth doesn’t depend on chemical transparency. In the Two-Dimensional Argument Against Materialism Dace says,

…it is worth noting that (contrary to a common supposition), the assumption that Q has the same primary and secondary intensions is not necessary for the [zombie argument] to go through. To see this, we can consider the version of the argument where we adjoin a “that’s-all” clause to P. From (1) (1) [P&~Q is conceivable] and (2) [If P&~Q is conceivable, then P&~Q is 1-possible], we can derive the conclusion that there is a minimal world verifying P in which the primary intension of Q is false. If P has the same primary and secondary intensions, then this world will be a minimal P-world in which the primary intension of Q is false. This world must differ from our world, because the primary intension of Q is true in our world…It follows that there is a minimal P-world that is not a duplicate of our world, so that physicalism is false of our world. It could be that strictly speaking physicalism will be true of consciousness, because P necessitates Q, but physicalism will be false of properties closely associated with consciousness, namely those associated with the primary intension of Q. We might think of this sort of view as one on which phenomenal properties are physical properties that have non-physical properties as modes of presentation.

But the claim here should be that transparency is required in order for (1) to be true. Consider the case of water and H2O. Since WATER is opaque may have seemed to Aristotle that he could conceive of a world where there was H2O but no water. He might have thought he could conceive of this because WATER is opaque. We cannot tell by either looking at water casually or examining our concept WATER that it is H2O. When a concept is opaque in this way we can conceive of worlds where the primary intension picks out something other than what it does here but we are not licensed to conceive of worlds where the secondary intension isn’t there unless we are in a position to say what the secondary intension of the concept is. Otherwise we would have to admit that Aristotle could conceive of a world physically just like ours without water! So the zombie argument does depend on transparency not as a way to get (2) as Philip suggested but as a way to get (1).