Thales of Miletus

Thales of Miletus was a Greek thinker of the early sixth century BCE whom Aristotle and most later Greek writers regarded as the first philosopher. He is credited with explaining the natural world through natural causes rather than the actions of the gods, proposing that everything comes from water, and with early achievements in geometry and astronomy. Nothing he may have written survives, so everything known about him comes from later authors, some writing centuries after his death.

Thales lived in Miletus, a wealthy Greek trading city on the coast of Ionia, in what is now western Turkey. Miletus had colonies around the Black Sea and close contacts with Lydia, Egypt and the Near East, which gave its citizens access to Babylonian astronomy and Egyptian practical mathematics. The traditional dates for Thales, around 624 to around 546 BCE, come from the chronographer Apollodorus and rest partly on guesswork; the one firmer anchor is the solar eclipse he was said to have predicted, which modern astronomers date to 28 May 585 BCE. Herodotus reports that his family had Phoenician ancestors, though most later writers treated him simply as a Milesian of good family.

The problem with Thales is the evidence. Ancient writers disagreed about whether he wrote anything at all; works attributed to him, such as a Nautical Star Guide, were doubted even in antiquity. The main sources are Herodotus in the fifth century BCE, Aristotle and his pupils in the fourth, and much later compilers such as Diogenes Laertius, writing around the third century CE, who collected anecdotes of uneven reliability. Aristotle himself often hedges, saying what Thales "is said" to have held. Any account of Thales is therefore a reconstruction, and separating the historical man from the legend of the first wise man is rarely possible.

According to Aristotle's Metaphysics, Thales held that the first principle, the source from which all things come, is water. Aristotle admits he is guessing at the reasons, suggesting that Thales noticed that nourishment and seeds are moist and that life depends on water. Thales also seems to have said that the earth floats on water like a log, an idea that may echo Egyptian and Mesopotamian creation stories in which the world emerges from a primeval ocean.

What made this matter was less the answer than the kind of question. Thales looked for a single underlying stuff that persists through change, and he offered an explanation that could be argued about and improved on. His fellow Milesians did exactly that: Anaximander proposed an indefinite, boundless source, and Anaximenes proposed air. This sequence of rival natural explanations is usually taken as the beginning of ancient Greek philosophy and of Western science.

Aristotle also reports two sayings that complicate the picture of Thales as a pure materialist: that the magnet has a soul, because it moves iron, and that all things are full of gods. Both seem to express the view that the world is alive and has its own sources of motion, rather than being pushed about by gods from outside.

Herodotus tells the most famous story. During a war between the Lydians and the Medes, day suddenly turned to night in the middle of a battle, and both sides, alarmed, made peace; Thales, he says, had foretold the year in which this would happen. Many historians doubt that anyone in the sixth century could have predicted a solar eclipse for a particular place, though he may have known Babylonian cycles that indicated when one was possible. Later writers credited him with fixing the solstices, dividing the year, and advising sailors to steer by the Little Bear rather than the Great Bear, as the Phoenicians did.

In geometry, the historian of mathematics Eudemus, a pupil of Aristotle, credited Thales with several basic theorems, including that a diameter divides a circle into two equal parts and that the base angles of an isosceles triangle are equal. Later sources say he proved that an angle inscribed in a semicircle is a right angle, still known as Thales's theorem, and that he measured the height of the Egyptian pyramids from their shadows and calculated the distance of ships at sea. Whether he gave proofs in the later Greek sense, as practised by Euclid, is unclear; the attributions may partly reflect a later wish to give geometry a founder.

Thales was counted among the Seven Sages of Greece, a traditional list of wise men, and many stories present him as a shrewd adviser. Herodotus says that Thales urged the Ionian cities to unite under a single council with its seat at Teos, so as to resist outside powers, and repeats, with some scepticism, a story that he diverted the river Halys so that the army of King Croesus of Lydia could cross it. Lydia fell in the 540s BCE to Cyrus the Great, bringing Miletus and the other Ionian cities under the Achaemenid Empire.

Two anecdotes pull in opposite directions. In Plato's Theaetetus, Thales falls into a well while gazing at the stars and is mocked by a Thracian servant girl for wanting to know what is in the heavens while missing what is at his feet. Aristotle's Politics answers the charge that philosophy is useless with the story that Thales foresaw a large olive harvest from the stars, rented all the olive presses in Miletus and Chios cheaply in winter, and made a fortune when the harvest came, showing that a philosopher could become rich if he wanted to. Neither story can be verified, but together they show how early he became a symbol of the thinker.

Diogenes Laertius reports that Thales died in old age of heat and thirst while watching an athletic contest, a detail of no more certain value than the rest of his biography.

Thales left no system and perhaps no book, yet his reputation as the founder has lasted. Aristotle's choice to begin his history of earlier thinkers with him fixed the conventional starting point of Greek philosophy, and the Milesian approach, seeking natural explanations and a single underlying principle, shaped the work of successors from Anaximander and Pythagoras, who according to some ancient reports met him, to the atomists. Modern scholars stress how little can be known for certain, but they generally accept that something new began in Miletus in his generation: the habit of explaining the world in terms that others could test, criticise and replace.