Kripke's Argument for Property Dualism: An Exposition
- Posted by Andrew Bailey on Tuesday, December 14, 2004 at 3:23 PM
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The Gauntlet is Thrown: An Argument for Dualism
If all identities are necessary, and all identity statements are necessary, a simple argument against mind/body physicalism can be constructed. It looks something like the following:
1. If my brain and my mind are identical, it is not possible that something is true of my mind and not of my brain
2. It is possible that something is true of my mind and not of my brain
3. My brain and my mind are not identical
Premise (1) can be understood as following from the Indiscernability of Identicals conjoined with a (modal) Law of Identity. That is, all things that are identical are identical necessarily and have all of and only the same properties. (2) can be defended on the grounds of intuitive thought experiments—a mind without a brain (cf. Descartes’ Meditations), or a brain without a mind (cf. David Chalmers’ The Conscious Mind).
The Duel Begins: A Physicalist Rejoinder
The obvious physicalist answer is to question (1)—this can be done via contingent identity statements. The physicalist here draws an analogy between two identity statements:
a) My mind and brain are identical
and
b) The city of which Gavin Newsom is the mayor is the same city as the transgender capital of the West Coast.
Identity statement (b) is true, but only contingently so—there are possible worlds in which it is false. The transgender capital of the West Coast really could have turned out to be Seattle and not San Francisco. Similarly, Gavin Newsom could have become mayor of Oakland or no city at all. These are not merely epistemic possibilities (“for all we know, Gavin Newsom might not be mayor of San Francisco”)—they are metaphysical.
All of this analysis yields a potentially rich payoff—contingent identity. If (a) really is like (b) in this respect, the physicalist has made substantial progress in dismantling an important argument for dualism. That some mind and body are, in some worlds not identical neuters the Cartesian argument for dualism without even contesting its second premise. This is not an argument for mind/body physicalism, but it is an argument for the possible truth of mind/body physicalism.
Enter the Dragon: Kripke’s Body Blow
Kripke’s understanding of how names function robs the physicalist of the above rejoinder. He grants that there are contingent identities—the Postmaster General is the inventor of bifocals and only contingently. This does not get the physicalist their prize, however, for a chasm of difference separates (a) and (b). In short, (a) uses rigid designation to refer, while (b) fixes its reference via connotation or description.
“My mind” in (a) refers to the same object in all possible worlds without any descriptive content. This denotation picks out the same object, regardless of what is true of the object —“that guy”—“this body.”
This notion of rigid designation, when applied to (a), shows the modal implications the physicalist is committed to—namely that my mind and brain are identical in all possible worlds. Joined with the apparent truth of (2), an apparent body blow has been dealt to physicalism.
Still Kicking: A Physicalist Answer
Kripke has given the physicalist a conceptual resource to maintain the signs of life, however: a posteriori (metaphysical) necessity conjoined with a form of (epistemic) contingency. Consider two identity statements:
c) Pain is the stimulation of C-fibers
and
d) Heat is molecular motion
(c) and its cognates are one contemporary way of understanding (a)—that is, brain states are identical to physical states. Mightn’t the physicalist hold (c) as analogous to (d)? (d) is an identity statement which is metaphysically necessary, given that “heat” and “molecular motion” are rigid designators. There is a loose (epistemic) sense, however, in which it could have been false, which Kripke notes: “In the case of some necessary a posteriori truths, however, we can say that under appropriate qualitatively identical evidential situations, an appropriate corresponding qualitative statement might have been false. (p.142, Naming and Necessity)”
In some possible world, it seems that we could encounter something that was qualitatively identical to (actual) heat that consisted, not of molecular motion, but of small gnomes finishing philosophy papers shortly before they were due.
This loose sense of “could have been false” might give the physicalist just the right elbow room to grant (2) , but still maintain identity between brain and mind (or brain states and mental states, or a particular brain event and a particular mental event). The powerful intuition of contingency that (2) and its cognates elucidate need not be denied. In this way, the physicalist can sidestep the central thrust of the initial argument for dualism.
The Last Word
This final sidestep is not available to the physicalist, Kripke argues. To say that “heat” could have turned out to be something other than molecular motion is to say that the same qualitative experience as feeling heat might have been caused by something other than molecular motion (roughly speaking), or that molecular motion could occur without the qualitative experience of feeling heat. This is all fine and dandy.
When transposed into mind/body terms, however, a far more controversial (and anti-intuitive) claim is being made: that a C-fiber could be stimulated without a qualitative experience identical to feeling pain, or that one could have a qualitative experience identical to feeling pain without C-fiber stimulation.
This turns out to be nonsense, however.
A strong disanology obtains between (c) and (d). (c) plays upon the two sense of “heat”—it’s objective (heat itself, whatever it consists of) and subjective (feeling heat) sides, so to speak. This is what gives the intuition that (c) could have been otherwise its force. In (d), however, there is no such ambiguity resides. Since pain just is a sensation, to have the same qualitative experience as one in pain is to be in pain. The two are (by definition?) the same thing. The possibility of one being in pain without C-fiber stimulation, then, has been granted, and the argument for dualism proceeds nicely.
