THALES OF MILETUS
(Copyright 1994-1998 Encyclopaedia Britannica)


A philosopher remembered for his cosmology based on water as the essence of all matter. According to the Greek thinker Apollodorus, he was born in 624; the Greek historian Diogenes Laërtius placed his death in the 58th Olympiad (548-545) at the age of 78. 
No writings by Thales survive, and no contemporary sources exist; thus, his achievements are difficult to assess. Inclusion of his name in the canon of the legendary Seven Wise Men led to his idealization, and numerous acts and sayings, many of them no doubt spurious, were attributed to him. According to Herodotus, Thales was a practical statesman who advocated the federation of the Ionian cities of the Aegean region. The Greek scholar Callimachus recorded a traditional belief that Thales advised navigators to steer by the Little Bear (Ursa Minor) rather than by the Great Bear (Ursa Major), both prominent constellations in the north. He is also said to have used his knowledge of geometry to measure the Egyptian pyramids and to calculate the distance from shore of ships at sea. Although such stories are probably apocryphal, they illustrate Thales' reputation. The Greek writer Xenophanes claimed that Thales predicted the solar eclipse that stopped the battle between the Lydian Alyattes and the Median Cyaxares, evidently on May 28, 585. Modern scholars believe, however, that he could not possibly have had the knowledge to predict accurately either the locality or the character of an eclipse. Thus, his feat was apparently isolated and only approximate; Herodotus spoke of his foretelling the year only. That the eclipse was nearly total and occurred during a crucial battle probably contributed considerably to his exaggerated reputation as an astronomer. 

In geometry Thales has been credited with the discovery of five theorems: (1) that a circle is bisected by its diameter, (2) that angles at the base of a triangle having two sides of equal length are equal, (3) that opposite angles of intersecting straight lines are equal, (4) that the angle inscribed in a semicircle is a right angle, and (5) that a triangle is determined if its base and the angles relative to the base are given. His mathematical achievements are difficult to assess, however, because of the ancient practice of crediting particular discoveries to men with a general reputation for wisdom. 

The claim that Thales was the founder of European philosophy rests primarily on Aristotle, who wrote that Thales was the first to suggest a single material substratum for the universe--namely, water, or moisture. Even though Thales as a philosopher renounced mythology, his choice of water as the fundamental building block of matter had its precedent in tradition. A likely consideration in this choice was the seeming motion that water exhibits, as seen in its ability to become vapour; for what changes or moves itself was thought by the Greeks to be close to life itself. To Thales the entire universe is a living organism, nourished by exhalations from water. (see also Index: element) 

Thales' significance lies less in his choice of water as the essential substance than in his attempt to explain nature by the simplification of phenomena and in his search for causes within nature itself rather than in the caprices of anthropomorphic gods. Like his successors Anaximander and Anaximenes, Thales is important in bridging the worlds of myth and reason. 
 

Copyright 1994-1998 Encyclopaedia Britannica