Heraclitus c. 535 BC – c. 475 BC

Heraclitus of Ephesus was a Pre-Socratic Greek philosopher of the late sixth and early fifth centuries BC, known in antiquity as the Obscure for the difficulty of his sayings. His one book, conventionally titled On Nature, survives only in roughly 130 fragments quoted by later authors. He is best known for the doctrine that everything flows, that strife and the unity of opposites underlie reality, and that an underlying logos governs the cosmos. His thought decisively influenced Plato, the Stoics, and modern philosophers including Hegel, Nietzsche, and Heidegger. The most famous saying attributed to him, that one cannot step into the same river twice, captures his central preoccupation with change.

Heraclitus of Ephesus (c. 535–475 BC) was one of the most distinctive of the pre-Socratic philosophers and the canonical philosophical voice of process and flux. The few biographical details that survive describe him as withdrawn, aristocratic, and disdainful of his contemporaries; he refused to take part in the political life of Ephesus and gave his book to the temple of Artemis rather than to public circulation.

Heraclitus's surviving fragments — about a hundred short, oracular sentences — reward and resist interpretation in equal measure. The most famous holds that all things flow, and that one cannot step into the same river twice. The unity of opposites — the way and the way down are one and the same; the path of the bow is its tension; war is the father of all — is the recurrent structural insight. The logos is the underlying rational principle by which the apparent chaos of becoming is governed, accessible to those who have learned to listen properly.

Heraclitus's nickname in antiquity was the Obscure for the difficulty of his fragments. Plato and Aristotle treated him as one of the founding figures of Western metaphysics, and Plato's distinction between becoming and being — the realm of flux and the realm of forms — is in significant part a response to him. Hegel and Nietzsche both treated him as a major philosophical predecessor. He remains one of the most-quoted pre-Socratic voices in twentieth-century continental philosophy.