Note: The following entry is from Dr. Owen Anderson (Arizona State University), a Fellow of the Institute for Classical Education
When did philosophy begin? We have a very specific date for this. May 28, 585 B.C. We can even narrow it down further to the time of day. I don’t know that any other discipline has such a specific start date. We can give such a specific date because we know this is when an eclipse occurred. And we date this as the beginning of philosophy because it was predicted by Thales of Miletus. But why is he the first philosopher? This sounds more like an advancement in astronomy. And many others, like the Babylonians, Egyptians, and Chinese, had been working on astronomy before Thales.
Thales is called the first philosopher because rather than giving an account of the cosmos that appeals to gods he gives a naturalistic account that appeals to matter. Others had been doing astronomy and connecting it to the gods or various spirits. Thales is able to predict the eclipse and make other advances by observation of natural causes. It is a change from the mythic age to the time of material explanations.
Thales asserted that all is water. In this you can see that he is an empiricist. By observation he noted that all things seem to be made from water (solid, liquid, gas) and grow due to water. By contrast, one does not observe the kinds of things described in the mythic age of the Iliad. And so Aristotle calls Thales the first of these philosophers because he was an empiricist, looking for the first principle of all things:
Of the first philosophers, then, most thought the principles which were of the nature of matter were the only principles of all things. 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 (Aristotle, Metaphysics, 983b).
Notice that the last sentence tells us what Thales believed to be eternal. There is no creation, all has existed and continues to exist, all is eternal. Aristotle describes the kinds of empirical observations that Thales may have used to come to his conclusion:
Thales, the founder of this type of philosophy, says this principle is water (for which reason he declared that the earth rests on water), getting the notion perhaps from seeing that the nutriment of all things is moist, and that heat itself is generated from the moist and kept alive by it (and that from which they come to be is a principle of all things). He got this notion from this fact, and from the fact that the seeds of all things have a moist nature, and that water is the origin of the nature of moist things (Metaphysics, 983b).
Also, Thales could be called a literalist. He looked for a naturalistic/literalist account of the myths.
Some think that even the ancients who lived long before the present generation, and first framed accounts of the gods, had a similar view of nature; for they made Ocean and Tethys the parents of creation, and described the oath of the gods as being by water, to which they give the name Styx; for what is oldest is most honourable, and the most honourable thing is that by which one swears. . . Thales at any rate is said to have declared himself thus about the first cause (Metaphysics, 984a).
These first philosophers, with Thales at their head, were empiricists, materialists, and literalists. They believed all is eternal. They asserted what we now call the conservation of energy. They gave naturalistic accounts to religious myths. We see their school continuing down to us today. We continue to see this as one of the ongoing influences on the Academy.