Thales was an ancient Greek philosopher born in Miletus in 620 BC best known for his belief that water is the fundamental principle of the world. Thales broke with the traditional view in Greece that events were caused by the will of the Olympic Gods, instead putting forth his water-based principle. In doing so, he was the first in ancient Greece to choose rationality and experience instead of myth to explain the past, present and future. For this reason, he is seen as both the first “philosopher” as well as the first “scientist” (i.e. natural philosophy) in the Western tradition.

Thales traveled throughout the ancient world gaining knowledge of Egyptian geometry as well as Babylonian astronomy. He is famously credited for five geometric theorems including the observation that a triangle inscribed in a semi-circle will always have a right angle. His wisdom was legendary and he is the only philosopher to be deemed one of the Seven Sages of Greece. He used his knowledge of astronomy to predict the eclipse of 585 BC, where the Lydians and the Medes who had been fighting for five years straight suddenly stopped due to the sun being blacked out in the middle of the day during a battle.

Thales recognized the importance of water for sustaining life. He saw that water could easily change from one state to the next, becoming vapor when heated, and ice when cooled. He reasoned that water is the ultimate principle (arche) of existence. In doing so, he was the first person in ancient Greece to break with the tradition that the Olympic Gods were responsible for creating the world and the events of the natural world. For example, instead of Poseidon, he saw the motion of subterranean water as responsible for earthquakes.

Thales saw water, not the Olympian Gods, as being divine. In ancient Greece, anything that can cause motion has a soul and is therefore living. Because water causes motion and is also eternal, Thales considered it the divine life-force of the world, responsible for its creation as well as all change. As such, he believed that “everything is full of Gods.” Likewise, because magnets cause motion in iron, as does amber when heated, he believed they have souls as well. This belief that things not normally considered to be alive are alive is called hylomorphism.

Due to his interest in astronomy, Thales also developed the legend of being the first “absent minded professor” in history. Plato tells us “Once while Thales was gazing upwards while doing astronomy, he fell into a well. A clever and delightful Thracian serving-girl is said to have made fun of him, since he was so eager to know the things in the heavens but failed to notice what was in front of him and right next to his feet.” (written in his dialogue Theaetetus)

He is also seen as the first person to show that philosophy is useful. Aristotle tells us “The story goes that when they found fault with him for his poverty, supposing that philosophy is useless, he learned from his astronomy that there would be a large crop of olives. Then, while it was still winter, he obtained a little money and made deposits on all the olive presses both in Miletus and in Chios. Since no one bid against him, he rented them cheaply. When the right time came, suddenly many tried to get the presses all at once, and he rented them out on whatever terms he wished, and so made a great deal of money. In this way he proved that philosophers can easily be wealthy if they desire, but this is not what they are interested in.” (written in his work Politics)

Thales is also considered the first person in ancient Greece to practice “natural philosophy.” He asked questions about nature of the earth and the heavens. He recognized the year can be divided into seasons, figured out dates for the solstices, and realized the year can be divided into 365 days. He is said to have recognized that the earth is shaped like a sphere, and to have proposed diameters for the sun and moon. He helped his fellow Milesian sailors and maritime traders by recognizing that it would be better to navigate by Ursa Minor instead of Ursa Major since it’s position in the sky changes less.

Five geometric theorems have been credited to Thales about the nature of circles and triangles. He is said to have been the first to introduce geometry to Greece, and that he learned geometry while traveling in Egypt. He observed the way they would remeasure land after flooding, and it is said that he figured out the height of a pyramid by measuring it’s shadow at a time of day when the two would be the same height. The five geometric theorems are: 1. that a circle is cut in half by its diameter 2. that when a triangle has two opposite sides of equal length their angles will also be equal 3. the intersection of two straight lines creates equal and opposite angles 4. a triangle inscribed in a semicircle creates a right angle, and 5. if the base of a triangle and the two angles at its base are known, then the triangle is known. And while Thales was unable to provide “formal” mathematical proofs, he could have easily proven these theorems through direct observation.

Thales benefited from living in a time and place which allowed for a good amount of freedom of thought and expression. As a city (polis), Miletus was aristocratic and secular, independent of large centralized religious and political institutions. Here, Thales was able to engage in a new way of thinking and discussion with other philosophers, notably Anaximander and Anaximenes, that encouraged asking questions, being critical, providing evidence or justification for one’s beliefs, and explaining things in a rational way. Together, Thales and the other Milesian philosophers sought to find explanations for nature in underlying principles rather than mythology. Thales was so revered, of a wise person it was exclaimed “The man’s a Thales!”