The Milesians. The philosopher-scientists whom tradition cites as being the earliest were all sixth-century Milesians, residents of the prosperous city of Miletus on the southern coast of what is now modern Turkey. Information about them is thin, and with the exception of a single phrase quoted nearly a millennium after the fact, we have no direct access to their work. Our fragmentary reports of their theories in fact usually come from summaries written much later, and from authors who had their own motives for attributing one idea or another to a particular thinker. Scholars must exercise extreme caution in presenting Milesian ideas and also in interpreting their meaning.

Heaven and Earth. Available evidence indicates two main directions or aims of Milesian research. On the one hand, they were concerned with the investigation of specific natural phenomena, such as earthquakes, lightning, and...