Concept
The Theaetetus (ˌθiːɪˈtiːtəs; Θεαίτητος) is a philosophical work written by Plato in the early-middle 4th century BCE that investigates the nature of knowledge, and is considered one of the founding works of epistemology. Like many of Plato's works, the Theaetetus is written in the form of a dialogue, in this case between Socrates and the young mathematician Theaetetus. In the dialogue, Socrates and Theaetetus attempt to come up with a definition of episteme, or knowledge, and discuss three definitions of knowledge: knowledge as nothing but perception, knowledge as true judgment, and, finally, knowledge as a true judgment with an account. Each of these definitions is shown to be unsatisfactory as the dialogue ends in aporia as Socrates leaves to face a hearing for his trial for impiety. As one of the major works of Plato's theory of knowledge, the Theaetetus was influential on Platonism from at least the time of the Skeptical Academy of the 3rd century BCE through the Neoplatonism of the 6th century CE. It has also been the subject of increased attention in modern times as a result of its influence on Edmund Gettier, who challenged the existing definitions of knowledge as a "justified true belief" in a paper that investigated Plato's theory of knowledge as outlined in this work. The Theaetetus is one of the few works of Plato that gives contextual clues on the timeline of its authorship: The dialogue is framed by a brief scene in which Euclid of Megara and his friend Terpsion witness a wounded Theataetus returning on his way home after from fighting in an Athenian battle at Corinth, from which he apparently died of his wounds. Euclid tells his friend that he has a written record of a dialogue between Socrates and Theaetetus, which occurred when Theaetetus was quite a young man. The dialogue is then read aloud to the two men by a slave owned by Euclid.