Miletus was an Ionian city; Ionia was a Greek colony on the Aegean coast of western Asia Minor. In the sixth century BCE, Miletus produces three philosophers: Thales, Anaximander, and Anaximenes. These philosophers were reputed to have sought the one, unchanging material principle (archê) of all things. Aristotle says of the first philosophers, which includes the Milesians:
Of the first philosophers, then, most thought the principles (tas archas) which were of the nature of matter (tas en hulês) were the only principles of all things (archas pantôn). That of which all things that are consist, the first from which they come to be, the last into which they are resolved (the substance remaining, but changing in its modifications), this they say is the element and this the principle of things, and therefore they think nothing is either generated or destroyed, since this sort of entity is always conserved, as we say Socrates neither comes to be absolutely when he comes to be beautiful or musical, nor ceases to be when loses these characteristics, because the substratum, Socrates himself remains, just so they say nothing else comes to be or ceases to be; for there must be some entity-either one or more than one-from which all other things come to be, it being conserved. (Metaphysics 983b)
2. Material Principle of All Things
Aristotle explains that the Milesian philosophers concentrate their efforts on ascertaining the principle (archê) of all things, which they consider to be matter (hulê). By matter is meant the four elements: earth, water, air and fire. By principle (archê) is meant that which which explains and causes the existence of another; an archê limits and conditions. Aristotle says that the Milesians sought to discover, "that of which all things that are consist, the first from which they come to be, the last into which they are resolved." They pursued this intellectual course because they believed that ultimately all things (or Being) was material and one; for them, to be able to say what everything is made of is to explain everything. In other words, what these men sought was to determine the origin and nature of everything by identifying the most basic material element that all things ultimately are, that from which all things emerge and return, or, as Aristotle puts it, the principle of all things, which is material. This is why Aristotle calls them "physicists" (physiki or physiologi), by which he meant those who believe that all things were physical, or made of matter. An implication of Milesian philosophy is that, ultimately there is no generation and destruction, since all things are one of the four elements. The changes that human beings experience are accidental and not substantial: water modifies its appearance but never ceases to be what it is, water.