Thales of Miletus

Thales was born in Miletus, a prosperous Greek city on the Aegean coast of Asia Minor, in what is now western Turkey. Ancient chronographers placed his birth around 650 to 620 BCE, with the later date more commonly cited; the doxographer Diogenes Laertius, drawing on the chronicler Apollodorus, linked his life to the 35th Olympiad ^[1]. Nothing he wrote survives, if he wrote anything at all, so every detail of his life reaches us through later authors, some writing centuries after his death. That distance means any Thales of Miletus biography must weigh anecdote against evidence with unusual care ^[2].

His parentage is recorded as Examyes and Cleobuline. Herodotus, the earliest source to mention him, noted a family background of Phoenician descent, though Diogenes Laertius reported that most writers considered him a native Milesian of distinguished stock ^[1][3]. Whatever his ancestry, Miletus shaped him. The city traded across the eastern Mediterranean and the Black Sea, planted dozens of colonies, and sat in constant contact with Egypt, Lydia, and Mesopotamia. A curious Milesian could absorb Babylonian astronomical records and Egyptian surveying techniques without leaving the harbor district ^[2].

Several ancient accounts state that Thales traveled to Egypt, where he studied with priests and encountered the practical geometry Egyptians used to resurvey fields after the Nile floods. The tradition is late and impossible to confirm, but it fits the pattern of Ionian merchants and mercenaries who moved freely through the Egyptian delta in the seventh century BCE ^[2][4].

Thales first appears in the historical record as a practical man of affairs rather than a cloistered thinker. Herodotus tells three stories about him, and all three concern public life. In one, Thales advised the Ionian cities to form a federal council at Teos to resist outside pressure, advice they did not take ^[3]. In another, he supposedly diverted the river Halys so that the army of Croesus of Lydia could cross, though Herodotus himself doubted the tale and noted that bridges already existed ^[3].

The most famous story is the eclipse. Herodotus wrote that during a battle between the Lydians and the Medes, day suddenly turned to night, an event Thales had forecast to the Ionians within the year in which it occurred. Modern astronomy identifies the likely event as the solar eclipse of 28 May 585 BCE, visible across Asia Minor ^[3][5]. Whether Thales could genuinely predict an eclipse is disputed; historians of science have argued he may have used Babylonian period cycles to estimate a window of risk rather than an exact date ^[5]. Either way, the report made his reputation in antiquity, and the eclipse remains one of the fixed points by which his lifetime is dated.

By the early sixth century BCE his fame was secure enough that Greek tradition enrolled him among the Seven Sages, the semi-legendary wise men honored for shrewd counsel. He is the only figure to appear on every ancient list of the seven, and Plato names him first among them in the Protagoras ^[1][6].

Aristotle called Thales the founder of natural philosophy, and that judgment anchors his place in intellectual history. In the Metaphysics, Aristotle reported that Thales identified water as the arche, the originating principle of all things, perhaps because moisture is essential to life, seeds, and nourishment ^[7]. The specific answer mattered less than the question. Thales asked what the world is made of and answered with a natural substance open to reasoned debate, not with the will of a god. Aristotle also preserved two other doctrines: that the earth floats on water like a log, and that all things are full of gods, a remark often read as meaning that soul or motive power pervades nature, since Thales reportedly argued that the magnet has soul because it moves iron ^[7][2].

Greek tradition also made him the father of deductive geometry. Proclus, drawing on the lost history of mathematics by Eudemus of Rhodes, credited Thales with bringing geometry from Egypt to Greece and with proving or stating several basic results: a circle is bisected by its diameter, the base angles of an isosceles triangle are equal, vertical angles are equal, and a triangle is determined by one side and its two adjacent angles ^[4]. The proposition that an angle inscribed in a semicircle is a right angle is still taught as the theorem of Thales. Historians debate how much of this reflects genuine proof in the later Euclidean sense, but the attribution shows that Greeks themselves traced demonstrative mathematics to him ^[4][8].

Practical measurement rounds out the list of Thales of Miletus achievements. He was said to have measured the height of the Egyptian pyramids by comparing their shadows with the shadow of a stick of known height, and to have devised a method for reckoning the distance of ships at sea, presumably by similar triangles ^[1][4]. In astronomy, beyond the eclipse, sources credit him with attention to the solstices, with estimating the angular size of the sun, and with advising sailors to steer by the constellation Ursa Minor as the Phoenicians did ^[1][5].

The ancient sources disagree about almost everything personal. On marriage, Diogenes Laertius transmits contradictory reports: some said Thales married and had a son named Cybisthus, others that he remained single and adopted his sister's son. When his mother pressed him to marry, he is supposed to have answered first that it was too early, and later that it was too late ^[1]. The anecdote is probably invented, like most sage stories, but it preserves the ancient image of a man absorbed in inquiry.

Two famous tales define that image from opposite directions. Plato tells the first in the Theaetetus: Thales fell into a well while gazing at the stars, and a witty Thracian servant girl mocked him for studying the heavens while missing what lay at his feet. Plato used the story to illustrate how philosophers appear absurd to practical people ^[6]. Aristotle tells the second in the Politics as a rebuttal. Reproached for his poverty, Thales used his knowledge of the weather to foresee a heavy olive harvest, quietly leased all the olive presses in Miletus and Chios during the off season, and rented them out at a profit when demand surged. Aristotle's moral was that philosophers can grow rich if they choose, but their ambitions lie elsewhere ^[9].

Both stories are illustrations rather than biography, yet they show how early and how completely Thales became a symbol: the impractical dreamer in one telling, the mind that masters the world in the other. Among reliable Thales of Miletus facts, perhaps the firmest is simply that within two centuries of his death Greeks were already arguing over what his life meant ^[2][6].

Thales seems to have remained active in Milesian affairs into old age. Herodotus records that he urged the Ionians toward political union before the Persian conquest of the coast, counsel that implies standing and long experience ^[3]. Later tradition also made him the teacher, or at least the older associate, of Anaximander, the Milesian who replaced water with the boundless apeiron as the first principle and who in turn taught Anaximenes. Through that chain the Milesian school carried the project of natural explanation forward for two generations ^[2][8].

His death is dated by Apollodorus and Diogenes Laertius to around the 58th Olympiad, roughly 548 to 545 BCE, which would make him well past seventy and by some reckonings close to ninety. Diogenes preserves a story that he died of heat, thirst, and the crush of the crowd while watching an athletic contest, and quotes an epigram calling him a sage who watched the games and was carried off by the sun he had studied ^[1]. Like much else, the scene is likely a literary flourish, but the approximate date is broadly accepted.

He died before Cyrus of Persia completed the conquest of Ionia in the 540s BCE, so he did not see Miletus pass under Persian control. The city's intellectual life outlived him; the tradition he started ran on until the Persian sack of Miletus in 494 BCE scattered its thinkers ^[2].

The scale of Thales's afterlife is out of all proportion to the certainty of his record. Aristotle's decision to begin his survey of earlier thinkers with Thales fixed him at the head of the Western philosophical tradition, and historians ever since have opened the story of Greek philosophy at Miletus ^[7][8]. The label commonly attached to him, first of the Presocratics, marks the shift he came to represent: from mythological accounts of the cosmos to explanations grounded in nature itself.

In mathematics his name is permanently attached to the inscribed angle theorem, and school students on several continents still learn the theorem of Thales, though the exact statement so named varies by country ^[4]. In the history of science he is honored less for any single result than for the wager behind them all, the assumption that nature is regular enough to be measured, predicted, and understood. Writers on the 585 BCE eclipse have called it a founding moment of scientific prediction, whatever method actually lay behind it ^[5].

Modern scholarship treats the individual claims about him with skepticism while accepting the outline: a Milesian of the early sixth century BCE, famous in his own lifetime for practical wisdom, credited within a few generations with turning curiosity about the world into a discipline. A crater on the Moon carries his name, standard reference works from the Stanford Encyclopedia of Philosophy to Britannica open their accounts of Greek thought with him, and the question that drove him, what is everything made of, remains the working question of physics ^[8][10]. Few figures known almost entirely through hearsay have shaped so much.