The Milesian school (/ - /,) was a school of Pre-socratic Philosophy of the 6th century BC, based in the Ionian town of Miletus. It is generally considered to be the first school of thought of Ancient Greek and thus Western philosophy. It consisted of three philosophers: Thales, Anaximander, and Anaximenes, who were all primarily interested in cosmology, and the origin and substance of the world. They each believed the world to be made of a fundamental element, an arche, and their philosophies, though differing in a number of ways, were similar in that they were all characterized by material monism and hylozoism.
They introduced new opinions contrary to the prevailing belief of how the world was organized, in which natural phenomena were explained solely by the will of anthropomorphized gods. The Milesians conceived of nature in terms of methodologically observable entities, and as such was one of the first truly scientific philosophies.
The Milesian school is not synonymous with the Ionian, which includes the philosophies of the Milesians plus distinctly different Ionian thinkers such as Heraclitus. The Ionian School contains the three philosophers that form the Milesian School as well as a few more who were added on during the 5th century, but the Ionian School looked more into the thought behind everything while the Milesian School was more focused on nature.