Thales of Miletus

Thales of Miletus (c. 625 – 547 c. BC) was a Greek pre-Socratic philosopher, astronomer, engineer, and mathematician. He is considered the founder of the Milesian School and one of the seven sages of Ancient Greece.

He sought to rationally determine a fundamental principle (arche) to explain the origin and constitution of physical nature (physis).


Thales, the son of Examyas and Cleobulina, was born around 625 B.C. in the Greek city-state of Miletus, in Ionia, which is now Turkey. His death took place in 547 B.C.[1]

According to the historian Herodotus, Thales of Miletus took an active part in the politics of his city, giving advice to the Ionians. He was described not only as a politician, but also as a great engineer. He managed to dig a deep canal in the river Halys, causing the waters to change direction, which allowed the army of Croesus to cross to the other bank. [2]

Thales Causing the River to Flow on Both Sides of the Lydian Army
Thales Causing the River to Flow on Both Sides of the Lydian Army, Salvator Rosa, c.1663, via Wikiart. Public Domain Image.


During his travel to Egypt, Thales had the opportunity to learn Egyptian mathematics and geometry, including the calculation of distances and heights based on the equality and similarity of triangles. He later took this knowledge back to Greece. [3] Furthermore, it is possible that his theory that the Earth floats on water also has Egyptian influence.[4]

Bust of Thales, unknown author
Bust of Thales, unknown author, 1825 – Alexander Onassis Foundation, via Wikimedia Commons. Public domain image.

Thales’ Theorem

Thales of Miletus is recognized as one of the first mathematicians in history, having made significant contributions to the fields of geometry and trigonometry.[5]

Thales’ theorem is a geometric principle which states that if two lines are cut by a transversal, the segments formed on the lines are proportional. With this theorem, he was able to measure the height of the pyramids in Egypt by observing the shadow cast by the sun.[6]

Prediction of a solar eclipse

According to Herodotus, Thales predicted the solar eclipse that occurred on May 28, 585 BC. The sudden change from day to night brought about the end of the war between the Medes and the Lydians.[7]

It is believed that Thales did not set an exact date, but an approximate one for the eclipse, and that his prediction came from his contact with the astronomical records of the Babylonians. The prediction of the eclipse may have been made through a series of empirical observations, rather than a more complex astronomical theory.[8]

On the other hand, some scholars dispute the veracity of this account entirely, pointing to the chronological and historiographical implications contained in Herodotus’ own work. “No real eclipse,” Mosshammer asserts, “meets the requirements of Herodotus’ narrative”.[9].

Discovery Of Ursa Minor

Thales of Miletus measured the constellation Ursa Minor, suggesting to Miletus’ sailors to be guided by it.[10] The constellations Ursa Minor and Ursa Major played a very important role in the navigations of that time.

Thales had a deep interest in astronomical observations. According to an anecdote told by Diogenes Laërtius in Lives and Opinions of the Eminent Philosophers, the philosopher was distracted by observing the stars and ended up falling into a well, and when he cried out for help, a woman told him:

You, O Thales, cannot see what is at your feet and you expect to see what is in the heavens?

DL, I, 1, 22 – 44.
The astrologer who fell into the well, Fable by Jean de La Fontaine
The astrologer who fell into the well, Fable by Jean de La Fontaine, 18th century illustration, via Wikimedia Commons. Public Domain image.


Some ancient sources attribute to Thales certain works, such as:[11]

  • Nautical Star-guide
  • On the Solstice
  • On the Equinox

However, modern scholars question the authenticity of such writings.[12] Some evidence points to this, such as the fact that Diogenes claimed that Thales wrote nothing, and attributed the Nautical Star-guide to Phocus of Samos.[13] Aristotle, from the cautious expressions he used when commenting on Thales’ philosophy, seems to have had no direct contact with any of Thales’ works.[14]

Tales, by Jacques de Gheyn III, 1616, British Museum.

Thales’s Philosophy

Thales’ main philosophical ideas are:

  • Water is the arche of all things
  • All things are full of gods;
  • All things have soul and life;
  • The earth floats on water;

Water as arche

According to Thales of Miletus, water is the fundamental principle (arche) that gives rise to all things. He came to this conclusion by observing that all things depend on moisture to survive.


Thales believed that the earth floats on water, moving like a ship. The earthquakes would be caused by the movements of the waters.[15]

The philosopher of Miletus was also said to be the first to determine the course of the sun from solstice to solstice; moreover, he stipulated the size of the sun, which would correspond to the 720th part of the solar circle.[16]


Thales believed that everything, including inert beings, possessed soul and life. This doctrine became known as hylozoism, a term derived from the Greek: hyle (matter) and zoe (life).

To prove this doctrine, he used the example of the magnet that attracts iron by magnetic force. The motion generated by the magnet would prove that all things have souls.[17]

Also, his statement that “everything is full of gods” can be related to the statement that everything has life.

Synoptic table

Thales of Miletus
Bornc. 625 BC. – Miletus
Diedc. 547 BC. – Miletus
WorksNothing wrote
SchoolMilesian School
Key IdeasWater as arche
InfluencesBabylonian astronomy
Egyptian geometry and mathematics


ABNT Style

ARISTÓTELES. Metafísica. Tradução de Edson Bini. São Paulo: Edipro, 2006.

BORNHEIM, Gerd A. (Org.) Os filósofos pré-socráticos. São Paulo: Cultrix, 1998.

BURNET, John. A aurora da filosofia grega. Trad. de Vera Ribeiro. São Paulo: Contraponto, 2006.

COPLESTON, Frederick. Historia de la filosofia, Grecia y Roma. Trad. Juan Manuel García de la Mora. México: Ariel, 1983.

DIÓGENES LAÉRTIOS (DL). Vidas e doutrinas dos filósofos ilustres. 2. ed. Tradução de Mário G. Kury. Brasília: Editora UnB, 2008.

EUCLIDES. Os ElementosTradução de Irineu Bicudo. São Paulo: UNESP, 2009.

HERODOTUS, Histories. Accessed 29 May 2023.

KIRK, G.S., RAVEN, J.E. e SCHOFIELD, M. Os Filósofos Pré-Socráticos: história crítica e seleção de textos. Lisboa: Fundação Calouste Gulbenkian, 1983.

MARÍAS, Julián. História da Filosofia. Trad. Claudia Berliner. São Paulo: Martins Fontes, 2004.

MOSSHAMMER, Alden A. Thales’ Eclipse. Transactions of the American Philological Association, v. 111, p. 145-155, 1981. Accessed 29 May 2023.

O’GRADY, Patricia F. Thales of Miletus: The Beginnings of Western Science and Philosophy. New York: Routledge, 2002.

SHIELDS, Christopher (editor). The Blackwell Guide to Ancient Philosophy. Blackwell Publishing ltd., 2003.

QUEREJETA, Miguel. On the Eclipse of Thales, Cycles and Probabilities. Culture and Cosmos, v. 15, p. 5-16, 2011. Accessed 29 May 2023.


  1. DL, I, 1, 22 – 44.
  2. HERODOTUS, I, 170, 75
  3. PROCLUS, Euclid’s Elements, I, p. 38: “And Thales, having first gone to Egypt, carried this theory to Greece, and on the one hand discovered many things, and on the other hand showed the principles of many to those after him.”
  4. KIRK et al. 1983, p. 90.
  5. O’GRADY, 2002: “Five Euclidean theorems have been explicitly attributed to Thales. There is general, but not unanimous, acceptance of this claim and of the accuracy of the sources
  6. DL, I, 1, 27.
  7. HERODOTUS, I, 74
  8. KIRK et al., 1983, p. 79.
  9. MOSSHAMMER, 1981, p. 151.
  10. KIRK et al., 1983, p. 81.
  11. KIRK et al., 1983, p. 83-84.
  12. KIRK et al. (1983) states, “The testimonies do not allow a firm conclusion, but what is likely is that Thales did not write a book.”
  13. DL, I, 1, 23.
  14. Expressions such as, “when judging by what is told,” or “the explanation which Thales is said to have given…”, show that Aristotle was not sure of the authenticity of the ancient opinions attributed to Thales.
  15. Seneca, Naturales quaestiones. III, 14.
  16. DL, I, 1, 24.
  17. ARISTOTLE, De anima, I, 2.

Cite This Work

Vieira, S. (2021, August 29). Thales of Miletus. Filosofia do Início. Retrieved from

Vieira, Sadoque. “Thales of Miletus.” Filosofia do Início, August 29, 2021.

Vieira, Sadoque. “Thales of Miletus.” Filosofia do Início, 29 Aug. 2021,


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