Thales of Miletus (estimated 624–546 BCE) was an early Greek philosopher. He is considered by many to be the first of the Greek philosophers.

Information about Thales is scattered and uncertain. If Thales wrote anything, it did not survive for very long. It seems that even Aristotle, who says that Thales was the first to do his kind of philosophy, did not have any writings of Thales to consult or quote directly. What is known about Thales can be found in the works of later philosophers and historians.

Thales broke away from mythology, using new methods to try to explain physical reality. In addition to his philosophy, Thales was a mathematician and an astronomer. He is said to have predicted a solar eclipse in 585 BCE, though it is uncertain whether he developed a method of predicting the eclipse himself.

Among Thales beliefs—and teachings—was that all things came from a single element: water, or, perhaps more specifically, moisture. Whether he meant that water was the origin of all things or that all things were fundamentally made up of water was unclear, though many scholars believe that the former is most plausible. Thales is said to have claimed that the Earth floated upon water, and that earthquakes could be explained by ripples in the subterranian ocean.

Thales’ philosophical focus was on natural philosophy, which would eventually come to be science. Thales was interested in what the world really was, apart from the implausible explanations given by the Greek mythology of his time. Thus, he began a tradition of seeking the ultimate nature of the universe from a physical, material perspective. Despite this, Thales did not seek to claim the non-existence of divinity, but rather reject the existing conception of divinity as was told by his contemporary religion.

The tradition of Thales and later Milesian philosophers was thus to explain nature. This tradition continued in Greece until Socrates, when philosophy turned inwards on humanity, focused on questions of human nature and conduct, bringing to the forefront aesthetics, moral philosophy and political philosophy. This division is sometimes known as the Socratic turn, and thus earlier Greek philosophers like Thales are known as pre-Socratic philosophers.

Thales is among the Seven Sages of ancient Greece, who are named in Plato’s Protagoras.