The famous phrase often attributed to Thales of Miletus (?624-526 BC) is is “[He]Who hateth suretyship is sure,” meaning – to hate given certainties is the first step to find out the real truth.

“And Thales, according to what is related of him, seems to have regarded the soul as something endowed with the power of motion, if indeed he said that the loadstone has a soul because it moves iron….Some say that soul is diffused throughout the whole universe; and it may have been this which led Thales to think that all things are full of gods.” Aristotle (de Anima).

Of the famous “Seven Sages” of Greece known through the classical word for their achievements in thought, Thales of Miletus is considered the most scientific member. Thales became a symbol in popular memory of the moment when oriental science and myth were morphing into the beginnings of classic Greek science – astronomy, geometry, mathematics, engineering and cosmology.

The word “physics” actually derives from the Greek plural phusika of the adjective phusikos, meaning "of or pertaining to nature.” Thales acquired legendary status in the rational study of nature in many areas. We cannot know if Thales actually achieved all that is credited to him – he left no written texts (other than a dubiously-attributed Nautical Astronomy in verse). In ancient Greece, it was traditional to assign great scientific and philosophical discoveries to pre-eminent men. But Herodotus and, later, Aristotle (among others) credit Thales with achievements that merit his fame.

Herodotus wrote that Thales was the first man ever to predict a solar eclipse that astronomers later assigned to 585 B.C. and also advised the fragmented Ionians to form a political union. Major discoveries were attributed to Thales in the fields of geometry and scientific measurement (such as calculating the height of the Pyramids in Egypt by measuring the length of their shadow), the study of solstices and measurement of the astronomical seasons. In particular, he was said to have elucidated original five mathematical theorems:

1. A circle is bisected by its diameter
2. Angles at the base of a triangle, which have two sides of equal length, are equal
3. Opposite angles of intersecting straight lines are equal
4. The angle inscribed in a semicircle is a right angle
5. A triangle can be determined if its base and the angles relative to the base are given.
Thales’ biographer, Diogenes Laertius, gave very little information about the man himself; it is said he was the son of Examyes and Cleobuline, distinguished Phoenicians, (although elsewhere said to be citizens of Miletus in Asia Minor); that he worked as an engineer; that he was the first natural philosopher of the Milesian School, and that he later taught Anaximander (611-545 BC). It was his discoveries that counted. He narrates anecdotes about him that are worthy of mention, even if they may be more tradition than fact. It is said that Thales advised navigators to steer a ship’s course by the Little Bear (Ursa Minor) rather than by the Great Bear (Ursa Major), both prominent constellations in the north: an idea also shared with the Phoenicians. Aristotle hinted that Thales, unlike other philosophers of his time, believed that the earth was spherical, rather than flat. He is said to have been the first man to construct an almanac based on the stars and seasons. He used his knowledge of geometry to calculate the distance from shore of ships at sea. Even if apocryphal, such diverse achievements illustrate his reputation for well-rounded brilliance in many fields.

As well as his mathematical theorems, Thales’ physical theses include:

1. The earth floats on water;

2. A magnetic stone has a psyche, since it makes things move

3. All things are filled with the gods; and

4. Water is the beginning or first principle of all things (Aristotle, Metamorphosis).

The claim that Thales was the founder of European philosophy rests primarily on Aristotle’s attention to Thales’ theory that water or moisture is the first principle. Given that Thales, as a philosopher, tried to renounce mythology, his choice of water as the fundamental building block of matter had its precedent in traditional Egyptian, Babylonian, and Jewish myths. He further argued that water exhibits properties of change, such as water becoming vapor; whatever exhibited change or movement, in Greek thought, was considered close to the building blocks of life itself. Thales conceived “things” in all aspects of life as being only varying forms of one fundamental and primary element of existence. He was able to conceive of the idea of underlying unity in the discordant diversity of the universe.

Proclus, the last major Greek philosopher, who lived around 450 AD, wrote:

[Thales] first went to Egypt and thence introduced this study [geometry] into Greece. He discovered many propositions himself, and instructed his successors in the principles underlying many others, his method of attacking problems had greater generality in some cases and was more in the nature of simple inspection and observation in other cases.

Although his “simple inspection and observation” was to be built on by later thinkers, Thales’ effort to move from a sheerly mythological view of existence to trying to elucidate the demonstrable causes was a major step forward in human thought. Like his successors Anaximander and Anaximenes, Thales is important in bridging the worlds of myth and reason.

An excellent in-depth analysis of Thales may be found at Thales of Miletus [Internet Encyclopedia of Philosophy]