One of Heidegger's most important works, this text gives a thorough explanation of what is arguably the most fundamental and abiding theme of his philosophy, namely the difference between truth as the "unhiddenness of beings" and truth as the "correctness of propositions". For Heidegger, it was by neglecting the former primordial concept of truth in favour of the latter derivative concept that Western philosophy, beginning with Plato himself, took off on its "metaphysical" course towards the bankruptcy of the present day. This book consists of a lecture course delivered by Heidegger at the University of Freiburg in 1931-32. The first part is a detailed analysis of Plato's "Allegory of the Cave" in "The Republic", while the second part gives an exegesis and interpretation of a central section of Plato's "Theaetetus". As always with Heidegger's writings on the Greeks, the point of his interpretative method is to bring to light the original meaning of philosophical concepts, especially to free up these concepts to their intrinsic power.