Theaetetus (dialogue)
Platonic dialogue investigating the nature of knowledge.
The Theaetetus 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, it is written in the form of a dialogue, in this case between Socrates and the young mathematician Theaetetus and his teacher Theodorus of Cyrene. The dialogue examines three definitions of knowledge—knowledge as perception, knowledge as true judgment, and knowledge as a true judgment with an account—each of which is shown to be unsatisfactory, ending in aporia as Socrates leaves to face a hearing for his trial for impiety.
- Author
- Plato
- Date
- Early-middle 4th century BCE
- Field
- Philosophy, Epistemology
- Language
- Greek (original)
- Form
- Dialogue
- Characters
- Socrates, Theaetetus, Theodorus, Euclid of Megara, Terpsion
- Known for
- Founding work of epistemology; influence on Edmund Gettier
Lore & Background
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 Theaetetus returning after fighting in an Athenian battle at Corinth, from which he apparently died. Euclid tells his friend that he has a written record of a dialogue between Socrates and Theaetetus, which occurred when Theaetetus was quite young. The dialogue is then read aloud to the two men by a slave owned by Euclid.
Reader's Guide
The Theaetetus is a foundational text in epistemology, as it systematically examines what knowledge (episteme) is. The dialogue presents and rejects three definitions: knowledge as perception (linked to Protagoras' 'man is the measure' doctrine and Heraclitean flux), knowledge as true judgment, and knowledge as a true judgment with an account. Each definition is shown to be unsatisfactory, and the dialogue ends in aporia. The work was influential on Platonism from the Skeptical Academy of the 3rd century BCE through Neoplatonism of the 6th century CE. In modern times, it gained increased attention due to its influence on Edmund Gettier, who challenged the definition of knowledge as 'justified true belief' in a paper that investigated Plato's theory of knowledge as outlined in this work. The dialogue is considered similar to Plato's earlier works in its aporetic ending, yet also resembles his later, more complex dialogues such as Parmenides and the Sophist.
Did You Know?
- The dialogue is framed by a scene in which Euclid of Megara and Terpsion witness a wounded Theaetetus returning from battle at Corinth.
- Socrates compares his philosophical method to midwifery (maieutics), helping young men give birth to thoughts.
- The dialogue ends in aporia, with no satisfactory definition of knowledge reached.
- The characters Socrates, Theaetetus, and Theodorus reappear the following day in the dialogue Sophist.
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