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Chalmers’s conceivability argument for dualism Anthony Brueckner 1. Introduction David Chalmers has defended dualism by arguing against the thesis of the supervenience of consciousness upon the physical, according to which no two possible situations are identical with respect to their physical properties while differing in their consciousness properties.1 Let P be the proposition that everything physical is arrayed as it actually is, and let C be the proposition that there is consciousness. Chalmers’s main argument against the supervenience thesis is very simple, stemming from considerations as old as Descartes: we can conceive of the truth of (P & ~C), by conceiving of a situation in which our physical duplicates are zombies, altogether lacking consciousness. Therefore, it is possible that (P & ~C), in the sense of ‘possible’ relevant to the metaphysical thesis of supervenience. Henceforth, I will use ‘Possible’ to express whatever notion is relevant to the supervenience thesis that Chalmers attempts to refute. That thesis can now be seen to be false, according to Chalmers, because the actual situation and the Possible situation in question are physically the same while the Possible one lacks consciousness. Everyone who has thought carefully about these matters knows that there is a prima facie worry about modal conceivability arguments like Chalmers’s: conceiving of the truth of f is not sufficient to establish the Possibility of f. The novelty of Chalmers’s attack on materialistic supervenience lies not in his conceivability argument itself, but rather in his complex answer to the foregoing Standard Objection. This answer, I think, 1
This is Chalmers’s formulation in Chalmers 1996.
Analysis 61.3, July 2001, pp. 187–93. © Anthony Brueckner
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has not been properly understood and addressed.2 In this paper, I will describe Chalmers’s answer to the Standard Objection, and I will argue that it is unsuccessful. In the aftermath of Chalmers’s complex manoeuvrings, we are left with nothing more than the conceivability of our zombie physical duplicates, and in the light of the Standard Objection, this is not enough by itself to refute the materialistic supervenience thesis. 2. Two-dimensional semantics Chalmers’s answer to the Standard Objection to his conceivability argument rests upon his two-dimensional semantics. He distinguishes two components of meaning in a way which can be best understood by considering ‘water’. The concept expressed by that word in English has two intensions, each of which is a function from Possible worlds to extensions. Consider the way in which the reference of ‘water’ is fixed in the actual world: the associated description ‘the dominant clear, drinkable liquid in the oceans and lakes’ (more briefly: ‘the watery stuff’) yields an actual-world extension for ‘water’ (57). This same actual-world reference-fixer yields an extension for each Possible world. Some of these extensions contain XYZ but not H2O, and some contain H2O but not XYZ. The primary intension of the concept of water is the function from each Possible world to the extension generated by applying the actual-world reference-fixer within the world. Now rigidify the description serving as the actual-world reference-fixer, say by attaching David Kaplan’s ‘dthat’ operator.3 Application of ‘dthat (the watery stuff)’ to the various Possible worlds then yields an extension for each world. These extensions contain only samples of H2O, and none of XYZ. The secondary intension of the concept of water is the function from each Possible world to the extension generated by applying the rigidified actual-world reference-fixer within the world. In contrast to the concept of water, the primary and secondary intensions of the concept of H2O coincide, according to Chalmers. The pertinent extensions for each Possible world contain only samples of H2O, and none of XYZ. Though Chalmers does not say, this is presumably because the descriptive actual-world reference-fixer for ‘H2O’ is something like ‘the stuff made of molecules having two hydrogen atoms and one oxygen atom’. That reference-fixer picks out H2O in all possible worlds, unlike ‘the watery stuff’. 2
For example, the authors in a recent symposium on Chalmers 1996 never address his answer to the Standard Objection given in the book. See Hill and McLaughlin 1999, Yablo 1999, and Loar 1999.
3
See Kaplan 1979.
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In setting up his two-dimensional semantics, Chalmers insists that there is but a single space of worlds. I will adhere to this view and call the worlds Possible worlds – those that are relevant to the metaphysical thesis of supervenience that is the heart of the Materialist/Dualist controversy under examination. At the level of statements (these seem to be propositions, given Chalmers’s usage), we can, however, distinguish between logical possibility and metaphysical possibility, on Chalmers view. He says, ‘Logical possibility’ comes down to the possible truth of a statement when evaluated according to the primary intensions involved. … The primary intensions of ‘water’ and ‘H2O’ differ, so it is logically possible in this sense that water is not H2O. (132)4 On the other hand, ‘Metaphysical possibility’ comes down to the possible truth of a statement when evaluated according to the secondary intensions involved … The secondary intensions of ‘water’ and ‘H2O’ are the same, so it is metaphysically necessary that water is H2O. (132) Let us return to Chalmers’s conceivability argument. To understand his answer to the Standard Objection that conceivability is not a guarantor of Possibility, we must see how the two-dimensional semantics handles the sentence ‘(P & ~C)’. We must consider the intensions of the crucial concepts. How is the primary intension of the concept of consciousness (call this the c-concept) determined? Chalmers finds it plausible to suppose that the actual-world reference-fixer for ‘consciousness’ is ‘has a phenomenal feel’ (134). So, given a Possible world, the primary intension of the cconcept yields an extension consisting of those states in that world that have a phenomenal feel. These are presumably themselves conscious states, on the conception of consciousness that takes it to be ‘the hard nut of the mind-body problem’, or ‘the hard problem’.5 The secondary intension of the c-concept is therefore the same as the primary intension: given a Possible world, the secondary intension yields an extension consisting of conscious states having a phenomenal feel.6 Let us consider the concept of being physical in the ways human bodies actually are (call this the p-concept). What is its primary intension? 4
Here Chalmers departs from his usual practice of speaking of the intensions of concepts expressed by words.
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The first appellation is Colin McGinn’s, in McGinn 1989. The second is Chalmers’s; see the Introduction to Chalmers 1996.
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Chalmers maintains that his answer to the Standard Objection goes through even if one somehow maintains that the primary and secondary intensions of the c-concept diverge. (133–34) I agree with his rejection of this view of the intensions, and I will return to this issue below.
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Chalmers’s view is that the pertinent actual-world reference-fixer will refer ‘by an extrinsic characterization’ of the pertinent entities (135). For ‘electron’, for example, actual-world reference is fixed by ‘the entity that plays the electron role’ (135). Though Chalmers does not specify a reference-fixer for the p-concept, let us assume that just as the primary intension of the concept of electron yields extensions containing only electrons, the primary intension of the p-concept yields extensions containing only human bodies physically just like ours. At any rate, Chalmers thinks that it is clear that the primary intension of the p-concept differs from the primary intension of the c-concept. He thinks that this follows from the fact (not here under dispute) that we can conceive of a situation in which our physical duplicates are zombies. This is the key to his answer to the Standard Objection, and we will return to it below.7 3. Chalmers’s answer to the Standard Objection Now for Chalmers’s statement of the Standard Objection, using his twodimensional semantic framework: The objection … comes down to the point that in using arguments from conceivability and the like, we have demonstrated the possibility of a zombie world using the primary intensions of the notions involved, but not using the more appropriate secondary intensions. While the primary intension of phenomenal notions may not correspond to that of any physical notion, the secondary intensions may be the same. If so, then phenomenal and physical/functional concepts may pick out the same properties … (132)8 You might think that Chalmers would attempt to answer the Standard Objection so formulated by attempting to show that the secondary intensions of the p-concept and the c-concept diverge. This would establish, in Chalmer’s framework, the metaphysical possibility of (P & ~C). However, 7
Chalmers in effect considers (134–36) the view that the secondary intension of the pconcept diverges from the primary intension. This would parallel the following situation: electrons have an intrinsic nature hidden from physical theory, so that the primary intension of the concept of electron, which involves only the extrinsic character of electrons, diverges from the secondary intension, which yields extensions containing only entities with the right hidden intrinsic character. I will follow Chalmers in rejecting this idea. I will assume that the p-concept’s primary and secondary intensions are the same.
8
Chalmers thus sees the Standard Objector as thinking of the proposition that our physical duplicates are conscious as an a posteriori necessity on a par with the proposition that water is H2O. He sees the Objector as thinking that the foregoing two propositions have a parallel intensional structure.
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Chalmers turns his back on the secondary intensions in giving his answer to the Standard Objection: we concentrate on the primary intension throughout [our answer] and ignore the secondary intension. … For note that whether or not the primary and secondary intensions [of a given concept] coincide, the primary intension determines a perfectly good property of objects in possible worlds. The property of being watery stuff [for example] is a perfectly reasonable property, even though it is not the same property as being H2O. If we can show that there are possible worlds that are physically identical to ours but in which the property introduced by the primary intension [of the c-concept] is lacking, then dualism will follow. (132) This sets up Chalmers’s answer to the Standard Objection: This is just what has been done with consciousness. We have seen that there are worlds physically just like ours that lack consciousness, according to the primary intension thereof [i.e. of its concept]. This difference in worlds is sufficient to show that there are properties of our world over and above the physical properties. (132–3) I reconstruct Chalmers’s rather compressed reasoning in this passage as follows. A concept’s primary intension determines a property possessed by all and only the objects found in the various extensions in the range of the function that is the primary intension. Let us call, for example, the property determined by the p-concept’s primary intension the p1-property. Now we reason: (1) The primary intension of the c-concept differs from the primary intension of the p-concept. [from the conceivability of the truth of (P & ~C)] (2) The c1-property differs from the p1-property. [from (1)] (3) The c1-property applies to things in our world. [obvious] (4) The only physical property of things in our world that is a candidate for being the c1-property is the p1-property. [obvious] (5) There is a property of our world over and above the physical properties, viz. the c1-property of having a phenomenal feel. [from (2), (3), (4)] Here is how the inference from (1) to (2) works. The divergence in primary intensions claimed in (1) arises from the alleged fact that there is a zombie Possible world in which the p-concept’s primary intension yields a nonempty extension E but in which the c-concept’s primary intension yields an empty one (there are allegedly no states having a phenomenal feel in the world in question). This means that the objects in the extension E have the p1-property but lack the c1-property. So those properties are different. (3)
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is indeed obvious. (4) is obvious if the p1-property is something like being physical in the ways human bodies actually are. (5) does follow in the indicated way. The key to the argument, then, is (1). Does the acknowledged conceivability of the truth of (P & ~C) really establish (1)? If so, then Chalmers has given a successful, novel answer to the Standard Objection as applied to his conceivability argument for dualism.9 4. The failure of Chalmers’s answer I now conceive of a situation in which our physical duplicates are zombies, but I am worried that, as can happen, it is not Possible that (P & ~C) even given my conception. I am unsure that there is a zombie Possible world, even given my conception. In short, I am worried about the Standard Objection to modal conceivability arguments. Chalmers’s answer to these worries is the above argument proceeding from (1). (1), though, rests upon the assumption that there is a Possible world in which the p-concept’s primary intension yields a non-empty extension containing our physical duplicates, while the c-concept’s primary intension yields an empty extension. So we need the assumption that there is a Possible world containing our physical duplicates but lacking states having a phenomenal feel, i.e. lacking conscious states. But where do we get that assumption? The only ground Chalmers has offered is that we can conceive of the truth of (P & ~C), by conceiving of our physical duplicates lacking consciousness. Now we are back to the original worry. The conception in question is not by itself sufficient to guarantee a Possible world containing our physical duplicates but lacking consciousness. To put the point slightly differently: Chalmers’s answer to the Standard Objection rests upon an inference from the conceivability of the truth of (P & ~C) to the Possibility of our physical duplicates lacking consciousness, in order to establish the divergence between primary intensions asserted in (1). But this is precisely the inference questioned by the Standard Objection as it applies to Chalmers’s conceivability argument. 9
It is worth noting that if the primary intension of the c-concept is the same as the secondary intension (as seems eminently plausible, since it seems eminently plausible that all and only states having a phenomenal feel are conscious states), then Chalmers can use (1) to show that the secondary intensions of the c- and p-concepts diverge. If the primary intensions of the two concepts indeed diverge, and the secondary intension of the c-concept is the same as the primary, then the secondary intensions of the two concepts must diverge. Chalmers correctly maintains that his argument proceeding from (1) is compatible with the odd view that the primary intension of the cconcept diverges from its secondary intension. In that case, one would have to say that the c1-property is not the property of being conscious. But the conclusion of his (1)-based reasoning, which espouses dualism with respect to the c1-property, would still stand.
shades and concepts 193 5. Conclusion In the end, Chalmers’s conceivability argument against the metaphysical thesis that consciousness supervenes upon the physical cannot withstand the Standard Objection. His two-dimensional semantics, once the details are worked through, turns out to license no novel answer to that objection. University of California, Santa Barbara Santa Barbara, CA 93106, USA
[email protected] References Chalmers, D. 1996. The Conscious Mind. New York: Oxford University Press. Hill, C. and B. McLaughlin. 1999. There are fewer things in reality than are dreamt of in Chalmers’s philosophy. Philosophy and Phenomenological Research 59: 445–54. Kaplan, D. 2001. Dthat. In The Philosophy of Language, ed. A.P. Martinich, 325–38. New York: Oxford University Press. Loar, B. 1999. David Chalmers’s The Conscious Mind. Philosophy and Phenomenological Research 59: 465–72. McGinn, C. 1989. Can we solve the mind-body problem? Mind 98: 349–66. Yablo, S. 1999. Concepts and consciousness. Philosophy and Phenomenological Research 59: 455–63.
Analysis 61.3, July 2001, pp. 193–202. © Jérôme Dokic and Élisabeth Pacherie
