The Theaetetus is one of the middle to later dialogues of the ancient Greek philosopher Plato. Plato was Socrates' student and Aristotle's teacher. As in most of Plato's dialogues, the main character is Socrates. In the Theaetetus, Socrates converses with Theaetetus, a boy, and Theodorus, his mathematics teacher. Although this dialogue features Plato's most sustained discussion on the concept of knowledge, it fails to yield an adequate definition of knowledge, thus ending inconclusively. Despite this lack of a positive definition, the Theaetetus has been the source of endless scholarly fascination. In addition to its main emphasis on the nature of cognition, it considers a wide variety of philosophical issues: the Socratic Dialectic, Heraclitean Flux, Protagorean Relativism, rhetorical versus philosophical life, and false judgment. These issues are also discussed in other Platonic dialogues.