Tom Stoneham

Paul Boghossian has argued that Externalism is incompatible with privileged self-knowledge because (i) the Externalist can cite no property to be the reference of an empty natural kind concept such as the ether; (ii) without reference there is no content; hence (iii) either we do know on the basis of introspection alone whether an apparent natural kind thought has content or not, in which case we can infer from self-knowledge and a priori knowledge of Externalism alone to the existence in our environment of water, gold etc.; (iv) or we do not know, without empirical investigation, whether an apparent natural kind thought has content. An Externalist not wanting to accept either (iii) or (iv) can deny (i). All empty natural kind concepts refer to the necessarily uninstantiated property of being identical to nothing. Since they have different senses and self-knowledge is only held to extend to the existence and identity of sense, this is compatible with privileged self-knowledge, and Externalism is still true of the concepts

Jessica Wilson has recently offered a more sophisticated version of the self-defeat objection to Cartesian scepicism. She argues that the assertion of Cartesian scepticism results in an unstable vicious regress. The way out of the regress is to not engage with the Cartesian sceptic at all, to stop the regress before it starts, at the warranted assertion that the external world exists. We offer three reasons why this objection fails: first, the sceptic need not accept Wilson’s characterization of the sceptical thesis and thus need not start her regress; second, even if she did commit to the regress, it would not undermine scepticism in the way Wilson envisages; and third, the appeal to mental state scepticism which is necessary to generate the second and subsequent steps in the regress is not justified.