Aristotle -- the main source on the philosophy and science of Thales -- considered him the founder of natural philosophy, the first to explain natural phenomena without recourse to mythology. Aristotle says he developed the scientific method, theories to explain why things change, and proposed a basic underlying substance of the world. Such an underlying principle is known as an archê, which in Thales' case was water. S. Marc Cohen at The University of Washington lists the following four Aristotelian passages and topics attributed to Thales:
- The earth rests on water. (De Caelo 294a28)
- Water is the archê of all things. (Metaph. 983b18)
- The magnet has a soul. (De Anima 405a19)
- All things are full of gods. (De Anima 411a7)
Thales started the field of Greek astronomy and may have introduced geometry into Greece after traveling in Egypt.
Together with Anaximander and Anaximenes, Thales formed the Milesian school of philosophy.
Main Source: IEP Thales.
Thales is on the list of Most Important People to Know in Ancient History.
74. After this, seeing that Alyattes would not give up the Scythians when Kyaxares demanded them, there had arisen war between the Lydians and the Medes lasting five years; in which years the Medes often discomfited the Lydians and the Lydians often discomfited the Medes (and among others they fought also a battle by night): and as they still carried on the war with equally balanced fortune, in the sixth year a battle took place in which it happened, when the fight had begun, that suddenly the day became night. And this change of the day Thales the Milesian had foretold to the Ionians laying down as a limit this very year in which the change took place. The Lydians however and the Medes, when they saw that it had become night instead of day, ceased from their fighting and were much more eager both of them that peace should be made between them. And they who brought about the peace between them were Syennesis the Kilikian and Labynetos the Babylonian: these were they who urged also the taking of the oath by them, and they brought about an interchange of marriages; for they decided that Alyattes should give his daughter Aryenis to Astyages the son of Kyaxares, seeing that without the compulsion of a strong tie agreements are apt not to hold strongly together. Now these nations observe the same ceremonies in taking oaths as the Hellenes, and in addition to them they make incision into the skin of their arms, and then lick up the blood each of the other.
Plato Protagoras 343
Such men were Thales of Miletus, Pittacus of Mytilene, Bias of Priene, Solon of our city, Cleobulus of Lindus, Myson of Chen, and, last of the traditional seven, Chilon of Sparta. All these were enthusiasts, lovers and disciples of the Spartan culture; and you can recognize that character in their wisdom by the short, memorable sayings that fell from each of them they assembled together and dedicated these as the first-fruits of their lore to Apollo in his Delphic temple, inscribing there those maxims which are on every tongue-"Know thyself" and 'Nothing overmuch.'