The following inquiry pursues two interlinked aims. The first is to understand Wittgenstein's idea of non-foundational certainty in the context of a reading of On Certainty that emphasizes its Pyrrhonian elements. The second is to read Wittgenstein's remarks on idealism/radical skepticism in On Certainty in parallel with the discussion of rule-following in Philosophical Investigations in order to demonstrate an underlying similarity of philosophical concerns and methods. I argue that for the later Wittgenstein, what is held certain in a given context (...) of inquiry or action is a locally transcendental condition of the inquiry or action in question. In On Certainty, Wittgenstein's analysis of the difference between knowledge and certainty forms the basis of his critique of both Moore's "Proof" and radical skepticism. This critique takes the shape of rejection of a presupposition shared by both parties, and utilizes what I identify as a Pyrrhonian-style argument against opposed dogmatic views. Wittgenstein's method in this text involves describing epistemic language-games. I demonstrate that this is consistent with the rejection of epistemological theorizing, arguing that a Wittgensteinian "picture" is not a theory, but an impressionistic description that accomplishes two things: (i) throwing into relief problems with dogmatic theories and their presuppositions, and (ii) describing the provenance of linguistic and epistemic practices in terms of norms grounded in convention. Convention, in turn, is not arbitrary, but grounded in the biological and social natures of human beings--in what Wittgenstein calls forms of life. Thus there is a kind of naturalism in the work of the later Wittgenstein. It is a naturalism that comes neatly dovetailed with Pyrrhonism--a combination of strategies traceable to Hume's work in the Treatise. I read Hume as someone who develops the Pyrrhonian method to include philosophy done "in a careless manner," and argue that Wittgenstein adopts a similar method in his later works. Finally, I explain the deference to convention in the work of both Hume and Wittgenstein by reference to a passage in Sextus' Outlines, on which I provide a gloss in the final chapter of this work. (shrink)