The Theaetetus is one of Plato's dialogues concerning the nature of knowledge, written circa 369 BC. In this dialogue, Socrates and Theaetetus discuss three definitions of knowledge: knowledge as nothing but perception, knowledge as true judgement, and, finally, knowledge as a true judgement with an account. Each of these definitions is shown to be unsatisfactory. The dialogue is framed by a brief scene in which Euclides tells his friend Terpsion that he has a written record of a dialogue between Socrates and Theaetetus, which occurred when Theaetetus was quite a young man. This dialogue is then read aloud to the two men by a slave boy in the employ of Euclides.