The very first of the Greek thinkers — the Ionians — lived in Asia Minor, in present day Turkey. They were speculative natural philosophers. Thales, who Aristotle considered the first philosopher, speculated that the various distinct objects of the world all had the same substratum. Underneath the appearance of division in the world, there was a basic material unity: All things were comprised of water. While this is a scientific statement about what comprises reality, it is also a metaphysical statement. It is maintaining a basic unity among diversity. We do not know precisely why Thales speculated that the common substance of all things was water. Aristotle speculated that it was because water is necessary for all living things. Water could also take the forms of solid (as ice), gas (as steam) and liquid (as water). In any case, what is remarkable about Thales’ view is not really the specific answer that he provides to the question. It is more the approach he initiates to address questions. He is not like the religious poet who comes bearing a message from the gods — his thoughts are not gifts of Hermes. Rather, he is speculating posting natural causes and using natural reason.
What Thales begins, various Ionian philosophers after him continue. Anaximander goes further than Thales, positing views about the origin of the diverse things in the world from a primordial unity. In the beginning was the apeiron, the boundless or unlimited, a nondifferentiated unity. Out of it the many things of the world emerge. Decisive here as a break in the explanatory model of the Greek religious-mythical thinkers, the emergence of the world does not occur because of the action of the gods. Neither Zeus nor Prometheus is involved. Rather, it is fundamentally the interaction of two factors — hot and cold — that are at work as the world emerges out of the unlimited. Animals are born from moisture heated by the sun. Humans originate from similar processes — natural and lawlike, even if not so clearly articulated as we might like (cp. Sassi, 40 ff.). Anaximenes continues reflections on these same issues. He proposes views contrasting with those of both Thales and Anaximander. Not water, he thinks, is the substratum, but air, aether. Following Anaximander, he appears to wonder that if all were comprised of water, how we would account for fire. Yet, in contrast to Anaximander, he posits a clearer mechanism through which the many arise from the original unity. The starting point for the development of the world was not the unbound, but was chaos. Out if it, from a primordial breath, the many arise.
One of the main characteristics that we see in these earliest Ionian thinkers is that they do not take the authority of their tradition as a starting point for their reasoning. While they are undoubtedly influenced by that tradition, they set out to reason on the basis of what they experience (cp. Jaeger, 102).
While Plato’s typology is extremely limited, given the importance of Plato’s philosophy, I will next focus on the views of Heraclitus and Parmenides — since understanding them is necessary for later understanding Plato.
Proceed to the Heraclitus.