Rush Rhees a close friend of Wittgenstein and a major interpreter of his work shows how Wittgenstein s On Certainty concerns logic language and reality - topics that occupied Wittgenstein since early in his career. Authoritative interpretation of Wittgenstein s last great work On Certainty by one of his closest friends. Debunks misconceptions about Wittgenstein s On Certainty and shows that it is an essay on logic. Exposes the continuity in Wittgenstein s thought and the radical character of his conclusions. Contains a substantial and illuminating afterword discussing current scholarship surrounding On Certainty and its relationship to Rhees s work on this subject.