Where the story starts, and how sure we can be
Greek tradition, followed by Aristotle, treated Thales of Miletus as the first philosopher. The claim is a convenient simplification. Earlier poets such as Hesiod already tried to order the world, in the form of a genealogy of gods, and the Near East had long traditions of cosmology and astronomy. What changed in sixth-century Miletus, on the western coast of Anatolia, was the style of explanation: three successive thinkers proposed natural principles behind the world and argued with one another’s proposals.
The evidence is thin. None of the Milesians’ writings survive intact. We know them through brief quotations and through later summaries, mainly by Aristotle and his students, who read them in terms of their own concepts. Dates are approximate, and many stories about them are anecdotes recorded centuries later.
Why Miletus
Miletus was one of the most prosperous of the Ionian Greek cities and a founder of many colonies around the Black Sea. Its ships and merchants carried ideas as well as goods. To the east lay Lydia, a neighbour whose capital and last king, the story of Sardis and Croesus, belongs to the same period, and later the Persian empire. Contact with Egypt and Mesopotamia exposed Greeks to older records of observation, including Babylonian astronomy, although how much any Milesian actually learned from them is debated.
Lydian influence extended to money. The Lydian gold coinage is among the earliest in the world, dated around the seventh and sixth centuries BCE, and coinage soon spread to Ionian cities. Some historians have suggested that a commercial setting based on measurement, exchange and abstraction encouraged abstract thought, though this is speculation rather than something the sources prove.
Political conditions may have helped. Ionian cities were self-governing, with no priestly class holding a monopoly on explaining the world. That is a plausible reason why open argument could flourish, but it is an interpretation, not documented fact.
Thales
Thales, who is placed in the late seventh and early sixth centuries BCE, left no surviving writings. Tradition makes him an all-round wise man: an engineer, a statesman and an astronomer. The best-known story is that he predicted a solar eclipse. Herodotus mentions that he foretold the year of an eclipse that interrupted a battle between the Lydians and the Medes, usually identified with the eclipse of 585 BCE. Modern scholars doubt that he had the means to predict a specific eclipse, and some think the tale is a later embellishment.
Aristotle reports that Thales held that water is the origin of all things, and that the earth floats on water. Aristotle offers possible reasons, such as that nourishment and seeds are moist, but he is guessing at Thales’s reasoning. Aristotle also reports that Thales said magnets and amber have “soul” because they move other things, which suggests he was explaining movement without appealing to a personal god acting from outside.
Later writers credit him with geometrical results, such as measuring the height of a pyramid from its shadow. These claims are uncertain, but they place him at the start of a tradition that would end with Euclid.
Anaximander
Anaximander, a younger Milesian active in the middle of the sixth century BCE, took a bolder step. He suggested that the origin of things cannot be any one of the familiar stuffs such as water, since opposites like wet and dry would then destroy each other. Instead he proposed the apeiron, usually translated “the boundless” or “the indefinite”, a source from which opposites separate and to which they return. A surviving fragment says that things pay penalty and retribution to one another for their injustice, according to the assessment of time. This language, borrowed from law, shows that he imagined natural processes as balanced and orderly.
His picture of the cosmos was original. Reports describe the earth as a short cylinder hanging in the middle of the universe without support, held in place because it has no reason to move in any direction. The heavenly bodies were rings of fire seen through openings. If these accounts are accurate, they present the earth as a body in space, which was a major change from earlier ideas. Later writers add that he drew a map of the known world and used a gnomon, a simple sundial, but such attributions are traditional and cannot be verified. Some accounts also credit him with an early theory that living things arose in moisture and that humans developed from other creatures, which should be treated cautiously as it comes from late summaries.
Anaximenes
Anaximenes, active somewhat later in the sixth century, went back to a specific substance: air. His contribution lay in the mechanism. Air, he held, becomes fire when thinned and then wind, cloud, water, earth and stone as it is thickened. This gave an account of how one basic stuff could turn into the variety of the world through condensation and rarefaction, processes that can in principle be observed. He is also credited with the comparison of the soul to air, which holds a person together, as air holds the cosmos together.
Whether air or water or the boundless is the better answer is less important than the logic. Each thinker criticised his predecessor: Anaximander’s point about opposites is a response to Thales, and Anaximenes’ mechanism responds to the vagueness of Anaximander. That kind of reasoned debate, in which positions are criticised and revised, is the clearest sign that something new had begun.
From myth to reason?
The old formula that Greece moved “from myth to reason” in Ionia is too tidy. The Milesians still spoke of the world as divine in some sense, and Greek cult continued unchanged. Yet they did something distinctive. They looked for explanations within nature rather than in the personal wishes of gods, they treated the cosmos as an ordered whole, and they presented their ideas openly so that others could criticise them.
Miletus itself did not remain a centre. The city was caught up in the Greco-Persian conflict, and after the Ionian revolt it was sacked by the Persians in 494 BCE. By then the new style of inquiry had spread, and later thinkers in Ephesus, Elea and Athens took up the Milesian questions.