In response to Philip Goff at the OCC David Chalmers has argued that his 2D argument against physicalism is not committed to what Goff called Phenomenal Transparency. PT, to a first approximation, is the claim the having a phenomenal concept allows one to know the true nature of the concept. Opaque concepts do not. Consider the concept of WATER. You can have full mastery of that concept and yet not know that water is H2O. This was the state of everyone prior to the discovery that water was H2O. I have argued that if we take the spirit of the identity theory and transpose it into the 2D framework we get a view that is immune to the zombie argument as this translates into the claim that the primary and secondary intensions for phenomenal concepts come apart. Dave now says that the zombie argument should none the less go through on such a view. It doesn’t depend on phenomenal transparency just like conceiving of Twin Earth doesn’t depend on chemical transparency. In the Two-Dimensional Argument Against Materialism Dace says,
…it is worth noting that (contrary to a common supposition), the assumption that Q has the same primary and secondary intensions is not necessary for the [zombie argument] to go through. To see this, we can consider the version of the argument where we adjoin a “that’s-all” clause to P. From (1) (1) [P&~Q is conceivable] and (2) [If P&~Q is conceivable, then P&~Q is 1-possible], we can derive the conclusion that there is a minimal world verifying P in which the primary intension of Q is false. If P has the same primary and secondary intensions, then this world will be a minimal P-world in which the primary intension of Q is false. This world must differ from our world, because the primary intension of Q is true in our world…It follows that there is a minimal P-world that is not a duplicate of our world, so that physicalism is false of our world. It could be that strictly speaking physicalism will be true of consciousness, because P necessitates Q, but physicalism will be false of properties closely associated with consciousness, namely those associated with the primary intension of Q. We might think of this sort of view as one on which phenomenal properties are physical properties that have non-physical properties as modes of presentation.
But the claim here should be that transparency is required in order for (1) to be true. Consider the case of water and H2O. Since WATER is opaque may have seemed to Aristotle that he could conceive of a world where there was H2O but no water. He might have thought he could conceive of this because WATER is opaque. We cannot tell by either looking at water casually or examining our concept WATER that it is H2O. When a concept is opaque in this way we can conceive of worlds where the primary intension picks out something other than what it does here but we are not licensed to conceive of worlds where the secondary intension isn’t there unless we are in a position to say what the secondary intension of the concept is. Otherwise we would have to admit that Aristotle could conceive of a world physically just like ours without water! So the zombie argument does depend on transparency not as a way to get (2) as Philip suggested but as a way to get (1).