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Thales Thales of Miletus [has been] since early antiquity regarded as the founder of the Ionian school of natural philosophy. Evidence suggests that he was a Milesian of Greek origin who flourished around 580 B.C. and that his field of distinguished activities included practical and political matters. There are indications that he visited Mesopotamia and Egypt, that he predicted the possiblity of an eclipse in 585 B.C., and that he proposed a simple doctrine on the origin and nature of the world. The most ancient references to Thales depict him as a man of exceptional wisdom. Later commentators associate him with specific discoveries in physics, metaphysics, astronomy, geometry, and engineering. Modern studies have hailed him as a proponent of the rational approach. However, recent conservative reconstructions of Thales’ ideas have called for the abandonment or modification of earlier estimates. In the absence of primary sources, several scholars have argued that the earliest testimony of Herodotus, Plato, and Aristotle must be preferred to later reports stemming from the doxographic tradition. Such a preference is necessary, they maintain, since Thales left no written documents, and most of the postAristotelian compilers depended for their comments on Aristotle’s reports. When the ancient evidence is carefully examined, these commentators hold, a believable picture of Thales’ thought emerges. The following is an outline of his thought, based on the early sources. Thales was very much concerned with the political conditions and developments in Asia Minor during his time: as an advisor he showed foresight in urging the Ionains to form a confederation against the Persians. As a “learned person” (sophos) he showed remarkable vision, correctly anticipating a solar eclipse during a battle between the Lydeans and the Persians. As an engineer he made the Halys River passable for King Croesus by diverting its waters. In his speculations Thales asserted with unprecedented boldness that the world originated in water and was sustained by water and that the earth floated on water. Inasmuch as there is natural change everywhere, he went on to claim, the world is animated, and even apparently inanimate objects possess psyche, the principle of self-motion. A fuller interpretation of the above necessarily takes one outside of the historically confirmable; yet one must propose some interpretation beyond the hard evidence if later fabrications are to be discarded. On the basis of Aristotle’s cautious remarks it can be inferred that Thales thought of the world as perfectly understandable through the idea of water - an element essential to life (and thus to self-motion), versatile, common, and powerful Thales, page 1 enough to account for every physical phenomenon. While there is very little elese that may be safely associated with Thales’ life and thought, post-Aristotlelian commentators persist in crediting him with many specific discoveries. They suggest that he discovered the solstices and measured their cycles, that he discovered the five celestial zones (arctic, antarctic, equator, and the tropics), the inclination of the zodiac, the sources of the moon’s light, and more. He is said to have explained the rise of the Nile as due to the etesian winds, and in geometry, to have discovered proofs for the propositions that the circle is bisected by its diameter, that the angles at the base of an isosceles triangle are equal, that two triangles are identical when they have one side and the angles formed by it with the other sides equal, and that in two intersecting straight lines the opposite angles at the intersection are equal. He was supposedly responsible for the axiomization of the field of geometry, and he was further credited with measuring the height of the pyramids and the distance of ships at sea. Most of these unsubstantiated ascriptions must be judged as unhistorical and inconsistent with the temper of the Milesian’s thought. Thales was the last representative of a tradition that respected myth, was fond of intuitions, and did not concern itself with proofs. To be sure, he was also the founder of a new approach, that of attempting to comprehend the world through reason alone. Thales, page 2