Thales studies nature

The story

Miletus, a city of merchants

Miletus was a rich Greek city on the coast of Asia Minor, in the region called Ionia, now in Turkey. Its ships sailed all over the Mediterranean and the Black Sea, and people, goods and ideas arrived in its harbour from Egypt, Lydia and Mesopotamia. In this lively setting lived Thales, between the end of the 7th and the middle of the 6th century BC. The exact dates are not known: the ancients gave 640 BC as his year of birth, while many modern scholars prefer 624. He died around 548–545 BC. Not a single writing of his has come down to us: everything we know comes from authors who lived long after him, such as Herodotus, Plato and Aristotle.

Explaining nature without the gods

To understand why Thales matters, think about how the Greeks explained the world before him. Earthquakes, lightning, the seasons, the seas: they were caused by the gods, and people told stories of angry or kindly deities. Thales tried a different path. He asked: what are all things made of? Is there something at the origin of everything? The Greeks called this principle “arche”. According to Aristotle, who speaks of it long afterwards, Thales answered that it was water. The reason, again according to Aristotle, was that nourishment, seeds and heat seem to be moist by nature. Today we know the answer was not correct, but what mattered was the way of reasoning: looking for an explanation inside nature and not in the will of the gods.

He is also credited with the saying “everything is full of gods”, and with the idea that the magnet, which attracts iron, and rubbed amber have a kind of “soul”, that is, a force that makes them move. These are not scientific discoveries in the modern sense, but they show a curious man who observed what really happened.

The eclipse of 585 BC

The most famous episode is told by Herodotus. While two peoples, the Medes and the Lydians, were fighting a long war in Asia Minor, during a battle day suddenly turned into night. The frightened fighters stopped the battle and made peace. Herodotus writes that Thales had announced this event to the Ionians in advance. Modern astronomers have calculated that the most likely total solar eclipse is the one of 28 May 585 BC. Some problems of chronology remain, however, and historians are not sure the events went exactly like this. How Thales could predict the eclipse remains a mystery.

Measuring the pyramids

Another story says that Thales, travelling in Egypt, measured the height of a pyramid without climbing it. According to Plutarch, he waited for the hour when the shadow of a stick planted in the ground was as long as the stick itself, and at that moment he measured the shadow of the pyramid. Another ancient author, Diogenes Laertius, gives a slightly different version: the shadow of a person was used. The reasoning is based on similar triangles, that is, on the idea that the shadow and the object are in a fixed ratio; it is the property we now call “Thales' theorem”. It is not certain that Thales really went to Egypt, but the anecdote says well what the ancients admired in him: the use of geometry to solve practical problems.

The ancients also credited him with a few theorems of elementary geometry, for example on the properties of triangles and circles. One author, Proclus, assigns some of them to him (the list varies according to the sources). Here too we must remember that we have nothing written by him, and tradition may have attributed to him discoveries made by others.

Anecdotes to take with a pinch of salt

Amusing little stories circulated about Thales. Plato tells how, while walking along looking at the stars, he fell into a well, and a young Thracian servant girl mocked him: he wanted to know the things of the sky but did not notice those at his feet. Aristotle, on the other hand, tells how, foreseeing an excellent olive harvest, Thales rented all the olive presses of Miletus and Chios cheaply and sublet them at a high price: he wanted to show that philosophers, if they chose, could easily get rich, but have other priorities. Modern historians think many of these episodes are not historical: they are invented stories meant to illustrate an idea about philosophy.

A teacher of teachers

Thales is considered the founder of the school of Miletus. His pupil was Anaximander, and Anaximander's was Anaximenes: the three, with different ideas, continued the search for the principle of all things. The ancients also placed him on the list of the Seven Sages, the wise men of archaic Greece. Plato, in the Protagoras, already names him among the seven. An old tradition says he was the first to receive this title.