Thales of Miletos

This story should be something that is instantly recognizable:

  His involvement in local politics is also rather anecdotal
  in nature, but Thales apparently impressed both sides of the
  ongoing conflict between the Lydians, Medes and Persians over
  the fate of the region of Ionia,

              when he predicted an eclipse of the sun

  which brought fighting to a standstill. He was also
  reportedly involved in the negotiations which followed the
  hostilities, and managed to obtain favourable terms for Miletus.

http://www.philosophybasics.com/philosophers_thales.html

The plain idea

Thales of Miletus (c. 624–546 BCE) is traditionally called the first philosopher in the Western tradition, and the reason is not any particular answer he gave. It is the kind of answer. Before Thales, if you asked why there are earthquakes, the answer was that Poseidon was angry. Thales said the Earth floats on water and earthquakes happen when the water is disturbed. He was wrong, and it doesn’t matter. He had swapped a story about gods for an explanation in terms of nature itself, one that could be argued with, tested and improved. That swap is the birth of philosophy and science.

None of his writings survive, if he wrote any. We know him through later authors, especially Aristotle and Herodotus, so treat the details as tradition rather than biography.

Why it matters

“All is water.” Thales proposed that everything comes from one basic substance, water. Again, wrong in detail, but it set the agenda: look for a single underlying principle (arche) behind the bewildering variety of things. His successors in Miletus proposed the “boundless” (Anaximander) and air (Anaximenes). The modern search for a theory of everything, from atoms to the Standard Model, is the same question with better tools.
Mathematics as proof. Thales is credited with some of the first geometrical theorems, general statements argued for rather than rules of thumb: a circle is bisected by its diameter, the base angles of an isosceles triangle are equal, and “Thales’ theorem”: any angle inscribed in a semicircle is a right angle.
Critical tradition. Thales seems to have encouraged his students to disagree with him. Karl Popper argued that this is what made Greek thought special: a school where criticising the master was allowed.

The eclipse

The story quoted above is the most famous: Herodotus reports that Thales predicted a solar eclipse, which occurred during a battle between the Lydians and the Medes, and the frightened armies made peace. Astronomers date it to 28 May 585 BCE, which makes it one of the earliest precisely datable events in Greek history. Historians of science doubt he could have predicted the exact day; he may have known Babylonian eclipse cycles well enough to say “this year”. Either way, the lesson that stuck was that the heavens follow patterns a human mind can grasp.

A worked example: measuring a pyramid with a stick

Another story says Thales measured the height of the Great Pyramid using only its shadow. Here is how it works, using similar triangles.

Plant a stick of height $s$ and measure its shadow $d$ . At the same moment measure the pyramid’s shadow $D$ (from the centre of its base). The sun’s rays make the same angle with both, so the triangles are similar:

\frac{H}{D} = \frac{s}{d} \quad\Rightarrow\quad H = D \times \frac{s}{d}

With a 1 m stick casting a 1.5 m shadow and a pyramid shadow of 219 m: $H = 219 \times \tfrac{1}{1.5} = 146$ m, almost exactly the Great Pyramid’s original height of about 146.6 m. Even simpler, wait until your own shadow equals your height, and then the pyramid’s shadow equals its height. No climbing required.

An everyday analogy: the mechanic versus the curse

Your car won’t start. One person says the car is cursed. Another says the battery might be flat. The second answer could be wrong, but it can be checked, and if it’s wrong you learn something and try the next idea. Thales was the first known person to be the mechanic about the whole universe.

The olive presses

Aristotle tells how people mocked Thales: if philosophy is so clever, why are you poor? So Thales, reading the weather, predicted a bumper olive harvest, quietly rented every olive press in Miletus during the winter, and then sublet them at a high price when harvest came. Having proved that philosophers could be rich if they wanted to, he went back to philosophy. It is often cited as the first recorded use of an option contract.

Common misconceptions

“Thales thought everything is literally made of water, like ice cubes.” Probably he meant water as the source and sustaining principle of things (it nourishes seeds, it can be solid, liquid or vapour), not that rocks are secretly wet.
“He rejected gods.” He is also quoted as saying “all things are full of gods”, perhaps meaning that matter itself is alive (a magnet “has a soul” because it moves iron).
“Philosophy began in Greece out of nowhere.” Thales drew on Egyptian geometry and Babylonian astronomy. What was new was the method of open argument.

How it connects

Pythagoras: the next great figure in early Greek mathematics, who may have learned from Thales.
Epicurus: the natural, god-free explanation carried to its conclusion.
Teleology and Philosophical Terms
Philosophers to Study

The truth revealed: Thales’ answer was wrong, and his question was so right that we are still asking it.