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Thales of Miletus

Little is known of Thales. He was born about 624 BC in Miletus, Asia Minor (now Turkey) and died about 546 BC in Miletos, Turkey


The bust shown above is in the Capitoline Museum in Rome but is not contemporary with Thales.

Thales of Miletus

Some impression and highlights of his life and work follow:

From W. K. C. Guthriegif we have

The achievement of Thales, has been represented by historians in two entirely different lights: on the one hand, as a marvelous anticipation of modern scientific thinking, and on the other as nothing but a transparent rationalization of a myth.

According to Guthrie himself, one may say that ``ideas of Thales and other Milesians created a bridge between the two worlds-the world of myth and the world of the mind."

tex2html_wrap_inline119 Thales believed that the Earth is a flat disk that floats on an endless expanse of water and all things come to be from water.

tex2html_wrap_inline119 But, more preciesly, Thales and the Milesians proceeded from the assumption of a fundamental unity of all material things that is to be found behind their apparent diversity. This is the first recorded monism in history. He also regards the world as alive and thus life and matter to be inseparable. Even plants he feels have a immortal ``soul".

tex2html_wrap_inline119 Being asked what was very difficult, he answered, in a famous apophthegm, "To Know Thyself." Asked what was very easy, he answered, "To give advice." To the question, what/who is God?, he answered, "That which has no beginning or no end." (The infinite!!)

tex2html_wrap_inline119 So the task of the philosophers was to establish what exactly provided this unity: one said it was water; another, the Boundless; yet another, air.

tex2html_wrap_inline119 Thales is believed to have been the teacher of Anaximander and he is the first natural philosopher in the Ionian (Milesian) School.

tex2html_wrap_inline119 Thales is also said to have discovered a method of measuring the distance to a ship at sea.


Five basic propositions with proofsgif of plane geometry are attributed to Thales.

Proposition. A circle is bisected by any diameter.gif
Proposition. The base angles of an isosceles triangle are equal.
Proposition. The angles between two intersecting straight lines are equal.

Proposition. Two triangles are congruent if they have two angles and the included side equal.
Proposition. An angle in a semicircle is a right angle.

Thales the Mathematician

Proposition. An angle in a semicircle is a right angle.


external Since there was no clear theory of angles at that time this is no doubt not the proof furnished by Thales.



  1. Dictionary of Scientific Biography
  2. Biography in Encyclopaedia Britannica
  3. F Ueberweg, A History of Philosophy, from Thales to the Present Time
     (1972) (2 Volumes).
  4. W K C Guthrie, The Greek Philosophers: From Thales to Aristotle (1975).
  5. D R Dicks, Thales, Classical Quarterly 9 (1959), 294-309.
  6. T L Heath, A History of Greek Mathematics I (Oxford, 1921).

next up previous
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Don Allen
Mon Feb 3 08:35:49 CST 1997