Heraclitus: Flux, Fire and the Logos

Heraclitus of Ephesus, active around 500 BCE, argued that change is the basic feature of reality. He is famous for the idea, reported by Plato, that you cannot step into the same river twice, since new waters keep flowing past. Yet Heraclitus did not think the world was chaos. He claimed that a hidden order, which he called the logos, governs all change, and that opposites such as day and night, or war and peace, are bound together in tension, like the strings of a lyre or bow.

He chose fire as the symbol of the world, since fire endures only by constantly consuming and transforming. Heraclitus wrote in short, puzzling sayings, earning the nickname 'the Obscure'. His importance lies in the questions he raised: if everything changes, how is knowledge possible? Parmenides, Plato and the Stoics all responded to his challenge.