Delving beneath the principal discourses of philosophy from Descartes through Kant, Bernard Freydberg plumbs the previously concealed dark forces that ignite the inner power of modern thought. He contends that reason itself issues from an implicit and unconscious suppression of the nonrational. Even the modern philosophical concerns of nature and limits are undergirded by a dark side that dwells in them and makes them possible. Freydberg traces these dark sources to the poetry of Hesiod, the fragments of Heraclitus and Parmenides, and the Platonic dialogues and claims that they rear their heads again in the work of Spinoza, Schelling, and Nietzsche. Freydberg does not set forth a critique of modern philosophy but explores its intrinsic continuity with its ancient roots.