 The question of how our perceptual beliefs are justified or known can be approached by first considering the question of whether they are justified or known. A prominent skeptical argument is designed to show that our perceptual beliefs are not justified. Versions of this argument (or cluster of arguments) appear in René Descartes’s Meditations, Augustine’s Against the Academicians, and several of the ancient and modern skeptics (e.g., Sextus Empiricus, Michel de Montaigne). The argument introduces some type of skeptical scenario, in which things perceptually appear to us just as things normally do, but in which the beliefs that we would naturally form are radically false. To take some standard examples: differences in the sense organs and/or situation of the perceiver might make her experience as cold things that we would experience as hot, or experience as bitter things that we would experience as sweet; a person might mistake a vivid dream for waking life; or a brain in a vat might have its sensory cortices stimulated in such a way that it has the very same perceptual experiences that I am currently having, etc.