Thales of Miletus and the Question of the Arche

Thales of Miletus, active around 585 BCE, is traditionally called the first philosopher. According to Aristotle, Thales claimed that water was the arche, the original source or underlying principle of all things. The answer may sound odd, but the question was revolutionary: instead of asking which god made the world, Thales asked what single material it is made of. Water was a reasonable guess, since it can be liquid, solid or vapor, and life depends on moisture.

Ancient sources also credit Thales with geometry learned in Egypt, measuring the height of pyramids by their shadows, and predicting an eclipse, though historians debate how much of this is legend. What matters most is his method: a natural explanation that later thinkers could disagree with and improve, which is exactly what his successors in Miletus did.