There’s no wonder that Thales of Miletus has been named the first of the Seven Sages of Greece. Throughout his life, he managed to impose a scientific way of thinking in many areas, from mathematics to philosophy. An undisputed scholar, he lived between from 624 to 546 B.C., and made a colossal contribution to mankind’s knowledge. In many ways, you could say that Thales changed the world, but what makes him widely popular are usually the theorems which revolutionized math.

Thales of Miletos

Philosophical ideas

Most of what we know today of Thales’ philosophy comes from Aristotle. Some believe that Thales left no writings whatsoever, but that’s still a matter of debate. Som think he wrote two works: ‘On the Solstice’ and ‘On the Equinox’, but neither of them still exists today.

The very first pre-Socratic philosopher, Thales’ main preoccupation was to define the substance(s) which form the world around us. For this reason, many call him the world’s first scientist. He was among the first to attempt a naturalistic explanations to material phenomena, using a scientific method which doesn’t resort to mystical or mythological explanations.

Thales also had vocal religious views: he believed in one single transcendental God, without a beginning or an end, who expresses itself through other gods. The philosopher’s idea of justice revolved around both the letter of the law and the spirit of the law – both justice and fairness were important to him. His idea of happiness included three major directions: a healthy body, a resourceful soul and a teachable nature.

Among his core ideas, one was especially important. It may seem like common sense today, but it was highly controversial during his life time: the idea that we should expect the same support from our children as we give to our parents.

However, Thales is chiefly known for his achievements in science and math. While meditating on the effects of magnetism and static electricity, he believed that the very power to move things without the mover itself changing was a characteristic of life; in other words, a magnet is also alive, in some way. If so, he believed, there would be no difference whatsoever between the living and the dead – if all things were alive, then these were supposed to have souls or divinities. The conclusion of this argument implied an almost complete removal of mind from substance, which, for the first time, opened the door to a non-divine principle of action. This is an idea philosophers are still working around to this day.


Thales is considered to be one of the most brilliant mathematicians in history. Today, we explicitly attribute five theorems to Thales, and he successfully applied two of them to the solution of practical problems.

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  • Definition:The circle is bisected by its diameter.
  • Proposition: In isosceles triangles the angles at the base equal one another, and, if the equal straight lines are produced further, then the angles under the base equal one another.
  • Proposition: The vertical and opposite angles are equal.
  • Proposition: Equality of triangles (by two angles and a side)
  • Proposition: The angle in a semi-circle is right angle.

Thales’ Theorem via

Theories about Earth

  • Water as the primary principle

Thales’ cosmological dictum claims water is the basic element (the primary principle) in everything. The idea that the entire world derives from water is an example of material monism (roughly similar to Anaximenes’ later idea that everything in the world is composed from air). According to Aristotle, the method by which Thales explained his theory was analyzing the biological principles. In the biological world, there were three things Thales turned to:

  1. all life depends on water – remove the water from a plant and it dies; deprive animals water and they dies;
  2. all seeds are themselves nothing but moisture;
  3. heat (in the form of sun and moon) is generated out of moisture and kept alive by it.

This last idea was based on the relationship between the heavenly bodies and the oceans.

Earth floating on water via

Thales believed that water was the origin of all things, the substance from which everything emerges and to which all things will return; moreover, he believed that things are ultimately water. Aristotle explains in ‘De Caelo’ that ‘[t]his [belief  is the most ancient explanation which has come down to us, and is attributed to Thales of Miletus’.

  • Earth is spherical

It is believed that Thales was the first one to claim that Earth has a spherical form, although there is no testimony to support this. In his work, Aristotle mentioned some of Thales’ ideas, but somehow he missed this one, so there is no actual proof of this geographic philosophy.

  • Earthquake theory

What we know of this theory is that, first of all, it’s very consistent with the hypothesis that Earth floats on water. This principle was applied to explain the nature of earthquakes, too. Seneca attributed to Thales the following theory: on the occasions when the earth experiences an earthquake, it is actually fluctuating because of the roughness of oceans. This explanation, albeit wrong, is the first one to explain a natural phenomenon without invoking any supernatural or mystical entities.


  • the eclipse

Image via Greek Names.

Thales is also believed to anticipated an eclipse of the sun – the one which occurred on 28th of May 585 B.C, according to Herodotus. Eudemus also mentioned Thales as being the first to discover the ‘eclipse of the sun and that its period with respect to the solstices is not always constant’.

  • the solstice

Diogenes Laertius mentioned that Thales ‘was the first to determine the sun’s course from solstice to solstice’, and also acknowledged the Astronomy of Eudemus as his source. It’s unknown how Thales got to the conclusion of solstices as a recurrent phenomenon, but Flavius Philostratus writes that: ‘[t]hales observed the heavenly bodies from Mount Mycale, which was close to his home’.

  • the seasons

Diogenes Laertius has written that ‘He (Thales) is said to have discovered the seasons of the year and divided it into 365 days’. The explanation for this is purely reasonable. Because of the determination of solstices and equinoxes, it’s only fair to presume that Thales could have also known the length of a solar year. Of course, it’s far-fetched to say that he discovered the seasons per se, given that the Egyptians have known about them for millenniums. But thanks to his understanding of the solar year, he may have related the information, thus being the first one to scientifically explain the seasons as we know them.