Theaetetus of Athens (; ''Theaítētos''; c. 417 – c. 369 BCE), possibly the son of Euphronius of the

Athenian Athens ( ) is the Capital city, capital and List of cities and towns in Greece, largest city of Greece. A significant coastal urban area in the Mediterranean, Athens is also the capital of the Attica (region), Attica region and is the southe ...

deme In Ancient Greece, a deme or (, plural: ''demoi'', δήμοι) was a suburb or a subdivision of Classical Athens, Athens and other city-states. Demes as simple subdivisions of land in the countryside existed in the 6th century BC and earlier, bu ...

Sunium, was a

Greek Greek may refer to: Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group *Greek language, a branch of the Indo-European language family **Proto-Greek language, the assumed last common ancestor of all kno ...

mathematician. His principal contributions were on

irrational Irrationality is cognition, thinking, talking, or acting without rationality. Irrationality often has a negative connotation, as thinking and actions that are less useful or more illogical than other more rational alternatives. The concept of ...

lengths, which was included in Book X of Euclid's ''Elements'' and proving that there are precisely five regular convex polyhedra. A friend of

Socrates Socrates (; ; – 399 BC) was a Ancient Greek philosophy, Greek philosopher from Classical Athens, Athens who is credited as the founder of Western philosophy and as among the first moral philosophers of the Ethics, ethical tradition ...

and

Plato Plato ( ; Greek language, Greek: , ; born BC, died 348/347 BC) was an ancient Greek philosopher of the Classical Greece, Classical period who is considered a foundational thinker in Western philosophy and an innovator of the writte ...

, he is the central character in Plato's eponymous Socratic dialogue. Theaetetus, like Plato, was a student of the Greek mathematician

Theodorus of Cyrene Theodorus of Cyrene (; 450 BC) was an ancient Greek mathematician. The only first-hand accounts of him that survive are in three of Plato's dialogues: the '' Theaetetus'', the ''Sophist'', and the ''Statesman''. In the first dialogue, he posits ...

. Cyrene was a prosperous Greek colony on the coast of North Africa, in what is now Libya, on the eastern end of the

Gulf of Sidra The Gulf of Sidra (), also known as the Gulf of Sirte (), is a body of water in the Mediterranean Sea on the northern coast of Libya, named after the oil port of Sidra or the city of Sirte. It was also historically known as the Great Sirte or G ...

. Theodorus had explored the theory of incommensurable quantities, and Theaetetus continued those studies with great enthusiasm; specifically, he classified various forms of irrational numbers according to the way they are expressed as square roots. This theory is presented in great detail in Book X of Euclid's ''Elements''. Theaetetus was one of the few Greek mathematicians who was actually a native of Athens. Most Greek mathematicians of antiquity came from the numerous Greek cities scattered around the

Ionia Ionia ( ) was an ancient region encompassing the central part of the western coast of Anatolia. It consisted of the northernmost territories of the Ionian League of Greek settlements. Never a unified state, it was named after the Ionians who ...

n coast, the

Black Sea The Black Sea is a marginal sea, marginal Mediterranean sea (oceanography), mediterranean sea lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bound ...

and the whole

Mediterranean The Mediterranean Sea ( ) is a sea connected to the Atlantic Ocean, surrounded by the Mediterranean basin and almost completely enclosed by land: on the east by the Levant in West Asia, on the north by Anatolia in West Asia and Southern ...

basin. He evidently resembled

in the snubness of his nose and bulging of his eyes. This and most of what is known of him comes from Plato, who named a dialogue after him, the ''Theaetetus''. He apparently died from wounds and

dysentery Dysentery ( , ), historically known as the bloody flux, is a type of gastroenteritis that results in bloody diarrhea. Other symptoms may include fever, abdominal pain, and a feeling of incomplete defecation. Complications may include dehyd ...

on his way home after fighting in an Athenian battle at

Corinth Corinth ( ; , ) is a municipality in Corinthia in Greece. The successor to the ancient Corinth, ancient city of Corinth, it is a former municipality in Corinthia, Peloponnese (region), Peloponnese, which is located in south-central Greece. Sin ...

, now presumed to have occurred in 369 BC; some scholars argue alternately for 391 BC as his date of death, the date of an earlier battle at Corinth.

Debra Nails Debra Nails (born November 15, 1950) is an American philosophy professor who taught at Michigan State University. Nails earned her M.A. in philosophy and classical Greek from Louisiana State University before going on to earn a Ph.D. in philosophy ...

, ''The People of Plato''. Indianapolis: Hackett Publishing, 2002; pp. 275–278 The crater Theaetetus on the

Moon The Moon is Earth's only natural satellite. It Orbit of the Moon, orbits around Earth at Lunar distance, an average distance of (; about 30 times Earth diameter, Earth's diameter). The Moon rotation, rotates, with a rotation period (lunar ...

is named after him.

References

External links

A Discussion of Theaetetus' Contributions to Euclid's ''Elements''
* {{DEFAULTSORT:Theaetetus Ancient Greek geometers 4th-century BC Athenians 410s BC births 369 BC deaths 4th-century BC Greek mathematicians

See also

References

External links