Greek philosopher, astronomer and geometrician, born in Miletus, Asia Minor.

Thales is the first philosopher of whom we have record who set himself the problem of explaining the universe in terms of one principle or "world-stuff". In philosophizing in terms of what Aristotle was later to call the "material cause", Thales was no doubt speculating out of wonder and for no utilitarian reason.

He lived in Greece between the years 640 and 550 BC. Thales was one of the Seven Wise Men of Greece and some of their sayings are still in common use today.

Thales is regarded as a pioneer in the sciences of geometry and astronomy. He is generally believed to have been the first man to foretell an eclipse of the sun (585 BC).

Philosophy is an investigation into the nature of reality, distinct from both the empirical sciences and from religious belief. First becomes explicit and self-conscious with the Greeks.

To the early Greek philosophers from Ionia, in Asia Minor, scientific investigation was still, to some extent, mixed with philosophical investigation. By empirical observation, some things are seen to be made out of other things, eg: ice from water. The Ionian philosophers, therefore, presupposing that there is some primary stuff or material out of which everything is formed, went on to ask: Of what is the world as a whole made?

Thales held that water is the primary material and that everything is made of water in various states. eg: ice is water in a frozen state, clouds are water in an evaporated state.

Thales became famed for his knowledge of astronomy after predicting the eclipse of the sun that occurred on May 28, 585 BC. He is also said to have introduced geometry into Greece.

According to Thales the original principle of all things is water, from which everything is again resolved. Prior to Thales, explanations of the universe were all mythological, and his concentration on the basic physical substance of the world marks the birth of scientific thought. Thales left no writings; our knowledge of him derives from an account in Metaphysics by the 4th-century BC Greek philosopher Aristotle.

Thales was the tutor and a friend of the Greek philosopher Anaximander.