ABSTRACT
The skeptic about the external world is a philosopher's fiction most closely associated with Rene Descartes. As long as there is a logical possibility that he is massively mistaken about the external world, Descartes, in his role as narrator of the Meditations, takes himself to lack the justification that knowledge of the external world requires. The kind of possibility that is relevant to external-world skepticism is an explanatory possibility—more particularly a possibility that is explanatory of some phenomenon or phenomena, knowledge of which is already assumed. The problem for the naturalist, as for more traditional metaphysical realists, is that, although there seems to be something unreasonable about external-world skepticism, strong objectivism depends on that same unreasonability. Skepticism must be treated as a real concern, because such a concern is what gives content to metaphysical realism's claim that the nature and existence of the world are independent of the reliability of our epistemic capacities.
