Abstract

This paper is mostly about the role of modal system S5 in conceivability arguments against, as well as in the defense of, different versions of physicalism. Jonathon VandenHombergh argued in a recent article that “[s]o far as the modal epistemology of reduction is concerned, therefore, it pays to go intrinsic.” His reasoning is that while the weaker, extrinsic version of reductive physicalism is vulnerable to conceivability arguments, the stronger, intrinsic, version is uniquely resistant to this type of challenge. To get to this surprising conclusion, VandenHombergh claims that the standard strategies of preempting the Dualist’s reasoning rely on some premise(s) that the Dualist can do without: one such premise is axiom-scheme S5. I will argue that the use of S5 is legitimate in countering the Dualist, as she herself relies on it, not to secure the validity of her arguments as VandenHombergh assumes, but rather, its soundness. I will also argue that this axiom-scheme is tacitly present in the auxiliary premises the stronger, intrinsic version of physicalism relies on: Kripke’s postulates about identity and non-identity statements. Indeed, this paper will forge an interesting and potentially important connection between Kripke’s postulates and modal system S5.