School based at sixth century BC and represented by the three philosophers of the Ionian city of Millet, on the coast of the Anatolia: Thalès de Milet, Anaximandre and Anaximène. They brought new opinions on the design of the world whose phenomena were explained by anthropomorphic whims of beings. Milésiens had nature in reference to observable entities and their approach, by his methodology, was one of the first philosophies really scientific.

Note:: It is necessary to make the difference with the Ionian École which includes at the same time the philosophers of the School milésienne and the philosophers Ionian such as Héraclite. See also the article on the Présocratiques.

Philosophy of nature

These philosophers defined each one in his way the primary substance, the principle (ἀρχή/ arkhè ), whose Universe was made up and who represented the source of the life. Thalès chose the Eau. But as it was impossible all to explain starting from this element (the Feu, for example), Anaximandre chooses a nonobservable and indefinite element, the apeiron (ἀπείρων). Because if each of the four traditional elements (water, air, fire and ground) is opposed to the three others, and if they are destroyed mutually, none could claim to constitute a stable bottom, not generated and imperishable. Consequently, one needs another entity of which each one of these elements comes, and who is truly this bottom bottomless.

The indefinite character of the apeiron raised criticisms which obliged Anaximène to specify it in the direction of a more concrete but subtle matter, the Air. This element according to its rarefaction or its condensation can change into other elements or substances such as fire, the wind, the clouds, water and the ground.

Cosmology

The differences between these three philosophers were not limited to the nature of the matter. Each one of them brought its design of the Universe. Thalès supported that the Ground floated on water. He noticed the movement of some star S to which he gave the name of Planet S. Anaximandre posed the Earth in the middle of a Universe made up of filled up concentric hollow wheels fire, openings of holes, the Sun, the the Moon and the other stars, and placed at various distances. For Anaximène, the Sun and the Moon were flat discs moved in a vault of heaven on which the stars were fixed.