-535 – -475
Heraclitus of Ephesus (c. 535–475 BCE) was a pre-Socratic Greek philosopher renowned for his doctrine of universal flux and the unity of opposites. He held that the Logos—a rational principle governing all things—underlies the ceaseless change of the cosmos, and that fire serves as the primary element symbolizing this perpetual transformation. His paradoxical, aphoristic style earned him the epithet 'the Obscure' in antiquity.
Formulated the doctrine of universal flux (panta rhei): 'You cannot step into the same river twice'
Introduced the concept of the Logos as a rational, governing principle of the cosmos
Argued for the unity and interdependence of opposites as constitutive of reality
Proposed fire as the primary arche (fundamental substance) of the universe
Pioneered a critical epistemology distinguishing genuine understanding from mere sense perception