VIII—Beliefs-in-a-Vat

Abstract

The over-arching claim that I intend to defend in this paper is that while widespread ‘local’ error is conceivable, we cannot, in the end, make sense of the radical sceptical idea that all our perceptual beliefs might be false – that no one has, as it were, ever been in touch with an ‘external world’ at all. To this end, I will show that an asymmetry exists between ‘local’ and ‘global’ sceptical scenarios, such that the possibility of ‘local’ error does not imply that ‘global’ error must also be possible. Instead, we will see that what gives rise to the radical sceptical problem is an unquestioned acceptance of the ‘New Evil Genius Thesis’ (NET) – the notion that I and my ‘envatted’ counterpart share the same perceptual experiences, even though my benighted twin has never had any contact with an ‘external’ reality. Although most contemporary epistemologists take NET for granted, I will show that it cannot, ultimately, be rendered intelligible, and, consequently, that neither can the ‘global’ sceptical scenario that depends on it.