Ludwig Wittgenstein's On Certainty explores a myriad of new and important ideas regarding our notions of belief, knowledge, skepticism, and certainty. During the course of his exploration, Wittgenstein makes a fascinating new discovery about certitude, namely, that it is categorically distinct from knowledge. As his investigation advances, he recognizes that certainty must be non-propositional and non-ratiocinated; borne out not in the things we say, but in our actions, our deeds. Many philosophers working outside of epistemology recognized Wittgenstein's insights and determined that his...