Semantic externalism and A Priori self-knowledge

The argument known as the 'McKinsey Recipe' tries to establish the incompatibility of semantic externalism (about natural kind concepts in particular) and _a priori _self- knowledge about thoughts and concepts by deriving from the conjunction of these theses an absurd conclusion, such as that we could know _a priori _that water exists. One reply to this argument is to distinguish two different readings of 'natural kind concept': (i) a concept which _in fact _denotes a natural kind, and (ii) a concept which _aims_ to denote a natural kind. Paul Boghossian has argued, using a _Dry Earth _scenario, that this response fails, claiming that the externalist cannot make sense of a concept aiming, but failing, to denote a natural kind. In this paper I argue that Boghossian's argument is flawed. Borrowing machinery from two-dimensional semantics, using the notion of 'considering a possible world as actual', I claim that we can give a determinate answer to Boghossian's question: which concept would 'water' express on Dry Earth?