Heraclitus (c. 535–475 BCE) lived in Ephesus, one of the brilliant Ionian cities then under Persian rule. Born to an aristocratic family, he renounced its political privileges and deposited his book in the Temple of Artemis. His sayings are short, riddling, often paradoxical, which earned him the ancient nickname *the Obscure*. Around 130 fragments are all that remain.

The famous formula *panta rhei* — 'all things flow' — may not be his own; Plato attributes it to him. But the core intuition is undeniably his: 'You cannot step into the same river twice, for other waters are ever flowing on to you, and you yourself are not the same.' What we perceive as stable objects are momentary knots in an ongoing process.

His second great concept is *logos* — at once word, measure, and the rational law of the universe. Logos is the immanent order that keeps the flux of things from collapsing into chaos. 'Opposites are one': day and night, life and death, war and peace are two faces of the same process, each requiring the other. Fire is his preferred image of the primary stuff, because fire even as it exists is constantly consuming and renewing itself.

His influence is everywhere in later thought: the Stoics put logos at the heart of their ethics; Hegel found dialectic in him; Nietzsche heard his own philosophy in *panta rhei*. His counter-pole would be Parmenides, who declared change an illusion. With these two figures the axis of Western metaphysics — flux against being — was set in place.