Conceivability arguments constitute a serious threat against reductive physicalism. Recently, a number of authors have proven and characterized a devastating logical truth centered on these arguments: namely, that their soundness entails the inconceivability of reductive physicalism. In this paper, I demonstrate that this is only a logical truth when reductive physicalism is interpreted in its stronger, intrinsic sense, as opposed to its weaker—yet considerably more popular—extrinsic sense. The basic idea generalizes: perhaps surprisingly, stronger forms of reduction are uniquely resistant to (...) the conceivability arguments opposing them. So far as the modal epistemology of reduction is concerned, therefore, it pays to go intrinsic. (shrink)

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. (shrink)