Joseph Levine, “Materialism and Qualia: The Explanatory Gap”

In “Naming and Necessity”1 and “Identity and Necessity,”2 Kripke presents a version of the Cartesian argument against materialism. His argument involves two central claims: first, that all identity statements using rigid designators on both sides of the identity sign are, if true at all, true in all possible worlds where the terms refer; second, that psycho-physical identity statements are conceivably false, and therefore, by the first claim, actually false.