Abstract

Chalmers argues that zombies are possible and that therefore consciousness does not supervene on physical facts, which shows the falsity of materialism. The crucial step in this argument – that zombies are possible – follows from their conceivability and hence depends on assuming that conceivability implies possibility. But while Chalmers’s defense of this assumption – call it the conceivability principle – is the key part of his argument, it has not been well understood. As I see it, Chalmers’s defense of the conceivability principle comes in his response to the so-called objection from a posteriori necessity. The defense aims at showing that there is no gap between conceivability and possibility since no such gap can be generated by necessary a posteriori truths. I will argue that while Chalmers is right to the extent that there is no gap between conceivability and possibility within the standard Kripkean model of a posteriori necessity, his general conclusion is not justified. This is because the conceivability principle might be inconsistent with a posteriori necessity understood in some non-Kripkean way and Chalmers has not shown that no such alternative understanding of a posteriori necessity is available