Thales of Miletus

Philosophy

• Arche Concept: Proposed that all things in the universe originate from a single fundamental substance — water (hydor). This represents the first systematic search for an "arche" (first principle) in the history of philosophy.
• Materialist Monism: Put forward the idea that all existing things can be reduced to a single substance.
• Hylozoism: Declared that "all things are full of gods," suggesting that even seemingly inanimate objects possess a kind of soul (psyche).
• Transition from Myth to Reason: Replaced mythological explanations of natural phenomena with methods based on reason and observation, without invoking the Olympian gods.

Mathematics and Geometry

• Thales' Theorem (the inscribed angle in a semicircle is always 90°)
• Intercept Theorem (proportional segments created by parallel lines cutting two transversals)
• Proved that a circle's diameter bisects the circle into two equal parts
• Demonstrated the equality of base angles in an isosceles triangle
• Proved the equality of vertical (opposite) angles
• Calculated the height of the Egyptian pyramids using shadow ratios
• Measured the distance of ships from shore using geometric methods

Astronomy

• Predicted the solar eclipse of May 28, 585 BC
• Determined the dates of the solstices and equinoxes
• Calculated the length of the year as 365 days
• Recommended using Ursa Minor for maritime navigation
• Attempted to calculate the sizes of the Sun and Moon

Engineering

• Diverted the course of the Halys (Kızılırmak) River to allow the Lydian army to cross

Economics

• Executed what is considered the first known futures or options contract in history through olive press speculation

Thales was a pre-Socratic Ancient Greek philosopher, mathematician, and astronomer regarded as the founder of Western philosophy and scientific thought. He established the Milesian (Ionian) School — the first known school of philosophy — and was counted among the Seven Sages of Ancient Greece.

He proposed that the fundamental substance of the universe is water (hydor), pioneering natural philosophy over mythological explanations. By seeking to explain natural phenomena through reason and observation rather than divine intervention, he became the first person to engage in what we now call science and philosophy. Aristotle considered him the first philosopher and his own intellectual predecessor.

His contributions to geometry and astronomy remain foundational; Thales' Theorem is still taught in classrooms worldwide. His prediction of the solar eclipse of 585 BC stands as one of the most remarkable scientific achievements of the ancient world.

Thales was born around 624–625 BC in Miletus, one of the most important trading cities in the Ionia region of western Anatolia (present-day Didim district, Aydın Province, Turkey). His father Examyas and mother Cleobulina belonged to a noble family known as the Thelidae.

According to ancient sources such as Herodotus and Diogenes Laërtius, this family was of Phoenician descent, tracing their lineage to Cadmus and Agenor. However, some modern historians argue that Thales was entirely Greek in origin and that the Phoenician attribution was a later addition. His father bore a Carian name while his mother had a Greek name, suggesting the possibility of mixed ancestry.

Diogenes Laërtius also provides a competing account, noting that "most writers represent him as a genuine Milesian and of a distinguished family." Miletus itself was a vibrant port city at the crossroads of Eastern and Western cultures, where ideas from different civilizations converged — an environment ideally suited to nurturing the young Thales' intellectual development.

Several ancient sources indicate that Thales visited Egypt at some point in his life and learned geometry there. The existence of Naucratis, a permanent Milesian trading colony in Egypt, makes this journey highly plausible. According to tradition, Thales established close relationships with the priests of Thebes, receiving instruction in astronomy and geometry — and, by some accounts, instructing them in geometry as well.

During his Egyptian sojourn, Thales is said to have measured the height of the pyramids by waiting until the moment when his own shadow equaled his body height and then measuring the pyramid's shadow. This method represents an early and elegant practical application of the principle of similar triangles.

A visit to Babylon is also considered probable. Some historians suggest that Thales acquired a significant portion of his astronomical knowledge from Babylonian sky-watchers. The influence of the sexagesimal system (base-60) on Greek thought is evaluated in this context. However, as the historian Roger L. Cooke notes, "this relation is controversial."

Thales was not merely a thinker; he was also an active political counselor. He maintained close relations with Thrasybulus, the tyrant of Miletus. According to Diogenes Laërtius, Thales advised the Milesians not to enter a military alliance (symmachia) with the Lydians. Thanks to this counsel, when King Croesus was defeated by Cyrus the Great of Persia, Miletus was spared.

Thales further advocated for the Ionian city-states to form a federated union against Lydia and Persia. He proposed Teos as the seat of this federation, suggesting that the other cities could continue to enjoy their own laws as if they were independent states.

One of the most celebrated episodes illustrating Thales' practical engineering ability comes from Herodotus. When King Croesus' army reached the Halys (Kızılırmak) River and could not cross, Thales ordered a canal to be dug behind the army's camp. Once the final dam was breached, the water flowed into the new channel, allowing the army to cross the old riverbed without even getting their feet wet.

Conflicting accounts exist regarding Thales' marriage. Some sources state that he married and had a son named Cybisthus (or Cybisthon), or that he adopted a nephew of the same name. Others report that he never married at all. According to Plutarch, when Solon asked Thales why he remained unmarried, Thales told his mother in his youth that it was too early and in his old age that it was too late.

One of the most famous anecdotes about Thales appears in Plato's Theaetetus: while gazing at the stars, Thales failed to notice a well in front of him and fell in, prompting a witty Thracian servant girl to mock him for being so eager to know what was happening in the heavens that he could not see what was right at his feet. This story became the archetypal tale of the absent-minded philosopher — absorbed in abstract thought while neglecting practical realities.

According to Diogenes Laërtius, Thales died during the 58th Olympiad (c. 548–545 BC) while watching the Olympic Games, overcome by heat exhaustion. He was approximately 78 years old at the time of his death.