Thales of Miletus (c.625-547 BC), a pre-Socratic philosopher, is regarded as the father of Greek philosophy, and the first Greek scientist and mathematician (although he was an engineer by training).

He belived that natural phenomena could be explained by laws rather than resorting to supernatural explanations.

Thales pictured the Earth as a flat disk that floated on an infinite ocean, perhaps motivated by observations that wood and other substances float on water. Water was important to him, as he saw it as the fundamental material from which everything else in the Universe developed. Compare his views with Anaximenes and Heraclitus who considered air and fire, respectively, to be the source of all other material.

Thales studied geometry in Egypt (where he calculated the height of a pyramid using geometric tools), and is credited with five theories covering the basic geometry of triangles and circles. Whether he ever proved them is another matter.

The Greek historian, Herodotus, attributes the prediction of a solar eclipse (on 28 May 585 BC during a battle between the Medes and the Lydians) to Thales. Thales may have been familiar with the Saros cycle of the Babylonian astronomers, but this would not provide him with sufficient information to make a true prediction. Although we can now make accurate predictions about when and where total eclipses will be seen, there is still a great deal of uncertainty as to how Thales would have done it!

None of Thales writings have survived, although it is not known whether he wrote that much. His philosophical and scientific ideas were documented by Aristotle in Metaphysics. Thales founded the Milesian school of philosophy of which Anaximander and Anaximenes were members.