Intrinsic phenomenal properties in color vision science: a reply to Peter Ross.

(1) I agree with Ross’s (1999), central claim: Color vision scientists implicitly accept a certain supervenience thesis of phenomenal properties of visual experience on internally individuated physiological properties of the visual system (I shall come back to the question of how the supervenience claim at issue should be spelled out in detail). He correctly points out that one of the premises that lead to the prediction that pseudonormal people would be red–green inverted is incompatible with a denial of that supervenience thesis. He is also, of course, correct in the following claim: Who accepts a supervenience thesis of the required kind thereby already excludes all those versions of functionalism that embrace some form of what he calls ‘‘phenomenal externalism.’’ From these observations Ross seems to conclude that the argument given in my 1996 paper amounts to a petitio principii until it is supplemented with some kind of independent support for the supervenience claim at issue. If this is what he means, then he may have misunderstood what I intended to show. My aim was, roughly, to show that certain versions of functionalism are incompatible with empirically established predictions of color vision science. The mere fact that there is this conflict should be a problem for functionalists since they typically believe that their claims about the meaning of mental terms reflect the way these terms are actually used in the empirical sciences and/or that their theory about the nature of mental states makes explicit what is implicitly accepted anyway about the nature of mental states in the relevant empirical disciplines. The conflict just mentioned shows that these assumptions are false. In order to establish that there really is this kind of conflict between color vision theory and the philosophical positions at issue, I obviously do not need to embrace, nor do I need to defend, the premises accepted in color vision science that are needed for a deduction of the conflict and I also do not need to embrace or defend the claims implicitly presupposed by these premises. (2) Once the conflict is established, the philosopher under attack can react in vari-