Thales of Miletus

Lore & Background

Thales's life is known mainly through the doxographer Diogenes Laërtius, writing eight centuries after his death, whose sources often contained unreliable or fabricated information. He was from Miletus, a mercantile city near modern Didim, Turkey. Herodotus described Thales as 'a Phoenician by remote descent,' but most writers represent him as a genuine Milesian of distinguished family. His father was Examyas and his mother Cleobulina; he may have married and had a son named Cybisthus, or remained single and adopted his nephew of the same name. Thales reportedly visited Egypt, where he may have learned geometry, though the evidence is disputed. He is also said to have traveled to Babylonia, but this too is uncertain. Thales is recognized as one of the Seven Sages of Greece, and the Delphic maxim 'know thyself' is attributed to him. He gained fame as a counselor, advising the Milesians not to ally with the Lydians, which spared Miletus after Croesus's defeat by Cyrus the Great. He also counseled the Ionian cities to establish a single seat of government at Teos. He was an engineer who allowed the Lydian army to cross the Halys River.

Reader's Guide

Thales's significance lies in his shift from mythological to rational explanations of the natural world. He theorized that all nature is based on a single ultimate substance, which he identified as water, and thought the Earth floated on water. This view was widely influential among his contemporaries. In mathematics, Thales's theorem and the intercept theorem bear his name. He is credited with introducing deductive reasoning and geometry to Greek thought, though his visits to Egypt or Babylonia for mathematical knowledge remain disputed. As an astronomer, he predicted weather and a solar eclipse, and his work on solstices and equinoxes advanced early science. Plutarch wrote that 'at that time, Thales alone had raised philosophy from mere speculation to practice.' His legacy as the first philosopher and scientist in the Greek tradition, and as one of the Seven Sages, established a foundation for Western philosophy and science. The uncertainty in his biographical details, however, reminds us that much of what is known comes from later, sometimes unreliable, sources.

Did You Know?

• He is the namesake of Thales's theorem in geometry.
• Thales reportedly allowed the Lydian army to cross the Halys River as an engineer.
• The Delphic maxim 'know thyself' is attributed to Thales.