On being a lonely brain-in-a-vat: Structuralism, solipsism, and the threat from external world skepticism

David Chalmers has recently developed a novel strategy of refuting external world skepticism, one he dubs the structuralist solution. In this paper, I make three primary claims: First, structuralism does not vindicate knowledge of other minds, even if it is combined with a functionalist approach to the metaphysics of minds. Second, because structuralism does not vindicate knowledge of other minds, the structuralist solution vindicates far less worldly knowledge than we would hope for from a solution to skepticism. For, solipsism threatens surprisingly vast swathes of worldly knowledge across multiple domains, including at least some knowledge about: political affairs, religious practices, artistic movements, historical events, and cultural trends. Third, the significance of these results exceeds their implications for the structuralist solution; these results suggest that no solution to external world skepticism which does not also solve the problem of other minds will ultimately yield the kind of solution we might have hoped for. Relatedly, these results suggest that the problem of external world skepticism should perhaps be construed as two different problems, since the problem might turn out to require two substantively different solutions, one for knowledge of the kind that is not dependent on other minds and one for knowledge that is.