1 To appear in M. O’Rourke and C. Washington (eds.), Situating Semantics: Essays on the Philosophy of John Perry (MIT Press) A REFUTATION OF QUALIA-PHYSICALISM Michael McKinsey Wayne State University Recent defenders of reductive physicalism such as Brian Loar (1990, 1997) and John Perry (2001) have adopted an intriguing new strategy:i (1) accept as so much common sense (nearly) everything that property-dualists want to say about sensory qualia, including the central claims that sensory qualia determine ‘what it’s like’ to have a given sense experience, and that persons are directly aware of these qualia in the having of such experiences; (2) contend that while these common sense facts about qualia may show that our ways of thinking and speaking about qualia are conceptually different from our ways of thinking and speaking about physical properties of the brain, these facts do not show that sensory qualia themselves (as opposed to our ways of thinking and speaking about them) are distinct from physical properties of the brain; (3) use this contention to turn aside the few existing arguments against reductive physicalism by such property dualists as Kripke (1972), Nagel (1974), Jackson (1982), and Chalmers (1996); and finally (4) insist that sensory qualia are in fact just identical with physical properties of the brain, so that consequently, the facts about the sensory qualities of conscious experience are nothing over and above physical facts about the brain. I will call the view that incorporates this strategy ‘qualia-physicalism’, or ‘Q-physicalism’ for short. In this paper I will argue that Q-physicalism is false. I agree that in the case of some words, notably indexical pronouns, proper names, and natural kind terms, there is an important semantic distinction between (a) the word’s conceptual or linguistic meaning, and (b) the particular contribution, which I call ‘propositional meaning’, that the word makes to the propositions expressed by use of sentences containing the word. This distinction makes it possible 2 in principle for there to be predicates that have distinct conceptual meanings and that nevertheless ascribe or predicate the same properties. However, or so I shall argue, the conceptual facts about predicates that ascribe sensory qualia, on the one hand, and predicates that ascribe physical properties to the brain, on the other, are sufficient to guarantee that the logical properties of what we say, the propositions we express, when we ascribe sensory qualia to our experiences, are quite different from the logical properties of what we say, the propositions we express, when we ascribe physical properties to the brain. It follows that propositions about the sensory qualities of conscious experience, and hence the facts that make these propositions true, are not the same as any physical propositions and facts about the brain. Hence, Q-physicalism is false. The question of whether Q-physicalism is true or false is crucial to our understanding of the mind-body problem. This is because the phenomenal qualities of sense experience are so difficult to incorporate in a physicalist world view, and it seems to me that Q-physicalism is the only form of reductive physicalism that is capable of taking qualia seriously. The Q-physicalists, in contrast for example to defenders of functionalist views of mental properties, can agree with non-reductivists like myself that sense experiences are distinguished by their qualitative features, features that determine ‘what it’s like’ to have the experience in question. The Q-physicalist’s distinctive claim is of course that these qualitative features of sensations are identical with physical properties of the brain, and it is this claim that I’m most interested in refuting.ii If I am right, then sensory qualia are not identical with any physical properties of the brain. Sensory qualia, I take it, are also not functional properties that logically supervene upon physical properties, since no functional property is sufficient to determine ‘what it’s like’ to have any given sense experience.iii Thus, if Q-physicalism is false, then it surely seems that sensory qualia are not reducible in any way to physical properties, and so no form of 3 reductive physicalism is true: the phenomenal properties of sense experience, and the propositions and facts involving the ascription of such properties, are properties, propositions, and facts ‘over and above’, and are not reducible to, any physical properties, propositions, or facts. So if I am right, only non-reductive forms of physicalism have a chance of being true. My arguments against Q-physicalism will rely crucially on claims about logical possibility, and in this respect they will resemble some of David Chalmers’ (1996) recent important arguments against reductive physicalism. Certainly, my discussion will be very much akin to Chalmers’, both in its spirit and in its conclusion. However, as we shall see, the concept of logical possibility on which I will rely is significantly different from the concept that Chalmers uses, making my arguments quite different from his, and allowing me to avoid certain objectionable assumptions about possible worlds that Chalmers’ arguments require. I will discuss Chalmers’ concept of logical possibility in detail below, after I’ve given my arguments against Q- physicalism. 1. Descartes’ argument for substance-dualism. In order to motivate and explain the concept of logical possibility on which I will be relying, it will be useful to consider an argument that I think may capture Descartes’ chief reason for believing that he is not a physical object.iv To state the argument succinctly, let ‘d’ be a name of Descartes, and define the property P as follows: x has P =df it is possible that: x exists, and there are no physical objects. Then the argument is simply: 4 (D) 1. d has P. 2. No physical object has P. ˆ 3. d is not a physical object. This argument certainly has a valid form. Moreover, each of its premises, taken separately, is plausible. Premise (D1) is plausible because as Descartes argued at length in Meditation II, it is consistent with all he knows for certain about himself as a thinking thing that he is a disembodied mind in a purely spiritual universe. So it certainly does not logically follow from the assumption that Descartes exists, that there are any physical objects. In this sense, then, it is possible that Descartes exists in a world devoid of physical objects, and premise (D1) is true. Premise (D2) is also plausible, but for a quite different sort of reason. Any physical object, it seems, would have to have a physical nature, or essence; such an essence would be a physical property without which the object in question could not exist. Thus no physical object could exist in a possible world in which it lacks its physical essence. Hence no physical object could exist in a possible world devoid of physical objects, for the simple reason that no physical object could exist in a possible world in which it itself is not a physical object. So in this sense, premise (D2) is true. But by now the reader should have begun to suspect that Descartes’ argument equivocates on two senses of the word ‘possible’. Premise (D1) is true when ‘possible’ is understood in a very weak sense to mean ‘logically possible’. In this weak sense, a proposition is logically possible just in case it is logically consistent, that is, fails to logically imply a contradiction. Let us say that a proposition p logically implies a proposition q just in case there is a correct deduction of q from p, a deduction whose only premises other than p are either logical truths or other necessary, conceptual truths that are knowable a priori, and every step of which immediately follows from 5 previous steps by a valid rule of inference.v Then we can say that it is logically possible that p if and only if the proposition that p fails to logically imply any explicit contradiction (of the form (q & ~q)). Note also that it follows from these definitions that if a proposition p fails to logically imply a proposition q, then it is logically possible that (p & ~q).vi (Note that these senses of logical implication and logical possibility are broadly rather than strictly logical, since I assume that these senses can apply or fail to apply by virtue of necessary a priori conceptual truths that may not be strict logical truths.) As we’ve seen, premise (D1) is true, given that the property P is understood in terms of mere logical possibility. But premise (D2) is false when ‘possible’ is understood in this weak sense. For just as the existence of Descartes fails to logically imply that there are any physical objects, so the mere existence of any object x fails to logically imply that there are physical objects, whatever that object x’s actual nature happens to be. Consider for instance the large, battered, old oak desk at which I am now writing, and call it ‘Fred’. Fred is of course the very paradigm of a physical object. But the simple singular proposition about Fred to the effect that Fred exists does not logically imply that there are any physical objects: no logical or conceptual truths that are knowable a priori will allow us to prove that there are physical objects, given merely the assumption that Fred exists. Of course we know that Fred has a physical nature, since Fred is a large oak desk. Even so, it no more follows from Fred’s existence that there are physical objects, than it follows from Descartes’ existence that there are such things.