Verificationism and the Zombie II
There are some points that need clarification, so let's review:
1. Evidence that there is a zombie cannot be found in any possible world. Therefore, such evidence is a logical impossibility. I suppose this is because there is a contradiction buried in the notion of "zombie for whose existence there is evidence." Perhaps it is that consciousness is by definition private (which would likely be because to have experience of a particular instance of consciousness is to be that instance.) "Evidencethat object o is not conscious other than o's physical and functional states" is incoherent.
[An aside: "evidence that there is a zombie" refers to first-order evidence. There is a possible world in which an honest and very intelligent person tells you that there is a zombie. But his testimony is second-order evidence. The point is that he can't have his opinion from bonafide first-order evidence; there is none of that in any possible world.]
Perhaps the fact that the concept of zombie is not incoherent (self-contradictory) misleads one into thinking that zombies are logically possible. There is more to logical impossibility of a thing than contradiction in its concept. A term X will fail to refer in any possible world if it is meaningless. And X can be meaningless because either (a.) X is self-contradictory in definition or (b.) X pretends to refer to something for which it is self-contradictory to claim that there is evidence that X correctly refers to it. When a person claims that there is an X and, upon our asking him to describe circumstances of warranted assertability of this claim, admits that there could never in any circumstances be evidence for his claim, we may conclude that X is a meaningless term.
2.Concepts can be large and diffuse clusters of various component concepts and experiences. So, one might be able to imagine things that are not logically possible. The imagination is powerful and can even sally forth without due regard to logical possibility. A zombie, who acts conscious but is non-conscious, may be fantasized about. He may therefore seem compellingly possible. But this is no argument against the verificationist dismissal of zombies that I've given here. It is merely the claim that my dismissal of them seems wrong.
3. Since evidential states that indicate a zombie existed are not possible and "zombie" is idle chatter like "round square" or "square with no corners," consciousness logically supervenes upon physical and functional states. "Zombie" is not a meaningful term because zombies are not logically possible. Since this is so, it is clear that consciousness is certain physical and funtional states.