An Interesting Corollary to the Principle of Perceptual Self-Exclusion

In my essay, An Argument Against the Identity Theory of Mind, I argued that the relation between a perceptual state and its perceptum entails the truth of the Principle of Perceptual Self-Exclusion. The Principle of Perceptual Self-Exclusion, it will be remembered, is the following: For any “perceptual state,” P, P is not a “perception of P.” Or, to put it another way: no existing or occurring perceptual state is identical to its own perceptum. Rather than rehashing the arguments that I provide in An Argument Against the Identity Theory of Mind, I will (for the purposes of this article at least) proceed as if the Principle of Perceptual Self-Exclusion has been successfully established. Now, the Principle of Perceptual Self-Exclusion can be isolated from the context and general argument of my original essay and be transposed in a manner that would strengthen many standard arguments against Materialism. To illustrate this, I will first present the “modified” Principle of Perceptual Self-Exclusion; I will then include a passage from a philosophy textbook which presents a “standard” argument against Materialism—and the Materialist’s “diffusion” of it; after that, I will show how a “modified” version of the Principle of Perceptual Self-Exclusion can be used to “diffuse” the Materialist’s “diffusion” of that “standard” argument against Materialism.

We may state the modified version of The Principle of Perceptual Self-Exclusion in the following way: For any “Object of Consciousness,” O, O is not identical to the “Consciousness of O.” Now, since no “Object of Consciousness,” O, is ever identical to the “Consciousness of O,” it follows that one cannot justify the assertion that the “Consciousness of O” is susceptible to being “masked” by appealing to the fact that certain “Objects of Consciousness,” O, are susceptible to being “masked.” Indeed, no amount of “masked” Morning Stars and Evening Stars will ever serve as grounds for holding that the “Consciousness of O” is susceptible to being “masked.” The reason for this is very simple, and follows immediately from our modified version of The Principle Perceptual Self-Exclusion. The Morning Star and the Evening Star are both “Objects of Consciousness,” O, and we have seen that no “Object of Consciousness,” O, can ever be identical to the “Consciousness of O.”

“Our first objection [to Materialism] derives from Descartes, who deployed a similar argument in support of strong dualism. It runs as follows: (1) I may be completely certain of my own experiences, when I have them. (2) I cannot have the same degree of certainty about the existence of any physical state, including my own brain-states. (C) So (by Leibniz’s Law) my conscious experiences aren’t in fact identical to brain states. Although both the premises in this argument are true, the argument itself commits a fallacy, and is invalid. For as we noted in Chapter 3:1, Leibniz’s Law only operates in contexts which aren’t intentional. It is obvious that the context reacted by the phrase “X is certain that…” is an intentional one. For example, the police may be certain that Mr. Hyde is the murderer, while they have no inkling that Dr. Jekyll is the murderer, despite the fact that Jekyll and Hyde are one and the same man. Oedipus may be certain that Jocasta loves him without believing that his mother loves him, despite the fact that Jocasta is his mother. So, from the fact that I have complete certainty about my own conscious states without having certainty about my own brain-states, it doesn’t follow that my conscious states aren’t brain states. For just as one and the same woman may be presented to Oedipus in two different guises—as Jocasta, and as his mother—so perhaps one and the same brain state may be presented to me under two different aspects: in a third-person way (as a brain-state), and via the qualitative feel of what it is like to be in that state.” (Carruthers, The Nature of the Mind: An Introduction, 67-68) 

Note, all of the examples which Carruthers gives in his reductio of the “Cartesian Certainty” argument (e.g. Dr. Jekyll and Mr. Hyde, and Jocasta and Oedipus’ mother) are all examples of “Objects of Consciousness” being “masked.” Not one of Carruthers’ examples are examples of the “Consciousness of Objects” being masked. In short, Carruthers’ has not in any way shown the argument to be invalid. On the contrary, it is Carruthers’ argument which is invalid. Carruthers mistakenly infers that the “Consciousness of Objects” is susceptible to being “masked” based upon the fact that certain “Objects of Consciousness” are susceptible to being masked—and such a move is, as we have seen above, an invalid one. Thus, Carruthers’ “diffusion” of the “Cartesian Certainty” argument has itself been “diffused” by our modified version of The Principle of Perceptual Self-Exclusion.