Thales of Miletus

Thales of Miletus ( THAY-leez) was a pre-Socratic Greek philosopher from the Ionian city of Miletus, in what is now Turkey. He lived roughly from the 620s to the 540s BC and is counted among the Seven Sages, the founding figures of ancient Greece. Starting in the eighteenth century, historians began to see him as the first philosopher in the Greek tradition, because he moved away from using mythology to explain the world and instead turned to natural philosophy. For this reason, he is also called the first person to practice mathematics, science, and deductive reasoning.

Thales believed that all of nature rests on a single ultimate substance, which he identified as water. He also thought the Earth floats on water. In mathematics, he gave his name to Thales's theorem, and the intercept theorem is sometimes called Thales's theorem as well. He is said to have calculated the heights of the pyramids and the distance of ships from the shore. As an astronomer, he reportedly predicted the weather and a solar eclipse. He is credited with discovering the position of the constellation Ursa Major, as well as the timings of the solstices and equinoxes. He also worked as an engineer, helping the Lydian army cross the Halys River. Plutarch wrote that, at that time, Thales alone had raised philosophy from mere speculation into practice.

Most of what we know about Thales's life comes from Diogenes Laërtius, who wrote *Lives and Opinions of the Eminent Philosophers* in the third century AD—about eight hundred years after Thales died. Diogenes's sources often contained unreliable or even fabricated information. Still, it is known that Thales came from Miletus, a trading city at the mouth of the Maeander River, near modern Didim, Turkey. His exact dates are uncertain, but they are roughly fixed by a few datable events. The historian Herodotus, writing in the fifth century BC, says Thales predicted a solar eclipse in 585 BC. Assuming a person's peak (or *floruit*) comes at age forty, the second-century BC chronicler Apollodorus of Athens placed Thales's birth around 625 BC.

On ancestry, Herodotus described Thales as "a Phoenician by remote descent." Diogenes Laërtius quotes Herodotus, Duris, and Democritus, who all agree that Thales was the son of Examyas and Cleobulina, belonged to the Thelidae (Phoenicians among the noblest descendants of Cadmus and Agenor), had been banished from Phoenicia, and was enrolled as a citizen in Miletus along with Neleus. However, Friedrich Nietzsche and others interpret this to mean only that his ancestors were seafaring Cadmeians from Boeotia. It is also possible he had mixed ancestry, since his father had a Carian name and his mother a Greek one. Diogenes also mentions an alternative account: most writers represent him as a genuine Milesian from a distinguished family. The 1952 *Encyclopedia Britannica* concluded that Thales was most likely a native Milesian of noble birth and certainly Greek.

Diogenes gives conflicting reports about Thales's family life. One says he married and either fathered a son (Cybisthus or Cybisthon) or adopted his nephew of the same name. Another says he never married, telling his mother as a young man that it was too early, and as an older man that it was too late. Plutarch tells a version where Solon visited Thales and asked why he remained single; Thales replied that he did not want to worry about children. Years later, anxious for family, he adopted his nephew Cybisthus.

The culture of Archaic Greece was heavily influenced by the Levant and Mesopotamia. It is said Thales was a trader and visited either Egypt or Babylonia, but there is no strong evidence he ever went to the Near East, and scholars dispute the issue. Later writers often attributed such travels to philosophers to explain the origin of their mathematical knowledge—as they did with Thales, Pythagoras, and Eudoxus.

Several ancient authors assume Thales visited Egypt at some point and learned geometry there. This is considered possible because Miletus had a permanent colony in Egypt, Naucratis. Some say he had close contacts with the priests of Thebes, who instructed him, or that he instructed them in geometry. He might also have known about Egypt from others' accounts without going there.

Aside from Egypt, Babylonia was the other mathematically advanced ancient civilization before the Greeks, and it is another common attribution for a mathematically-minded philosopher. Historians Roger L. Cooke and B.L. Van der Waerden argue that Babylonian mathematics influenced the Greeks, pointing to the use of the sexagesimal (base-60) system. Cooke notes this relation is controversial. Other historians, like D. R. Dicks, reject the idea of Babylonian influence on Greek mathematics, because the sexagesimal system was unknown in Greece until around the time of Hipparchus (c. 190–120 BC). Herodotus wrote that the Greeks learned the gnomon from the Babylonians, and Thales's follower Anaximander is credited with introducing it to the Greeks. Herodotus also says the practice of dividing the day into twelve parts, and the *polos*, came from the Babylonians—though this too is disputed.