Heraclitus

Heraclitus belonged to the royal family of Ephesus and gave the hereditary priesthood to his brother. He was said to be haughty, contemptuous of the crowd and equally of Homer, Pythagoras and every learned man. He deposited his book in the temple of Artemis; its style was brief and riddling like an oracle, and the ancients called him 'the Obscure'. About one hundred and thirty fragments survive.

His central insight is that the world is not a thing but a process. 'You cannot step twice into the same river', because the water keeps flowing. Yet flux is not chaos: it follows a measure he called the Logos. Fire is the emblem of this process, burning yet remaining fire, sustaining itself through constant consumption and transformation.

He insisted equally on the unity of opposites: the road up and the road down are one road, sea water is life to fish and poison to men, war is the father of all. Harmony is not the abolition of opposition but its tension, like the bow and the lyre. Hegel said there was no proposition of Heraclitus that he had not taken into his Logic.