Moody's overall argument, as presented above, is obviously formally valid, since it's a simple modus tollens. And, as indicated above, I think his sub-argument for (1), though vague, can be victoriously specified via routes I myself have mapped . The problem is the extraordinarily vague premise (2). The first source of obscurity concerns Moody's underlying modal notions. In order to analyze these notions, let us use g as a variable ranging over groups of zombies visiting us from another world. And let us deploy the traditional symbol `' from modal logic to say that some proposition or state of affairs p is logically possible (and to say that some proposition p is logically necessary, where iff ). Finally, use the predicate P to denote ``penetrability," where the idea is that if zombies can be found out, if they can be revealed as zombies, they are said to be penetrable. One possible contrual of (2), given this (humble) machinery, and the fact that Moody's gedankenexperiments (as is common) are designed to show that certain propositions are coherent, and hence logically possible, is
Or have we? Isn't it perfectly easy to imagine that a group---call it the `A Team,' or simply, later, `a'---of zombie visitors perform always and only those behaviors in keeping with the presence of consciousness? After all, there is certainly some set of utterances, and some set of bodily movements, which preclude any inferences to the proposition that the bearers of these utterances and movements are not conscious. Whatever clever questions humans pose to the A Team, they come back with the ``right answers." For example, with respect to the inverted spectrum problem, there is certainly some set of sets of responses that precludes any suspicion that those giving these responses are zombies. (That there is such a set of sets follows immediately from the undeniable fact that we don't suspect, when hearing about ISP from human philosophers, that they may be zombies.) Surely it is conceivable that the A Team invariably responds with a set of behaviors from this set.
But now the A Team thought-experiment gives us