Theaetetus is one of Plato’s dialogues, written circa 369 BC. It is a dialogue between Socrates and the mathematician Theaetetus, in which they attempt to define “knowledge.” Living between 428/7 to 348/7 BCE, Plato was one of Socrates’ students, and much of what we know of Socrates’ philosophy comes from Plato’s writings. Plato, as well as Socrates’ other students (such as Aristotle and Xenophon), laid the foundation for modern Western philosophy.
Plato has thirty-five dialogues ascribed to him, though it is uncertain whether he actually wrote all thirty-five. There is also uncertainty surrounding what order Plato wrote his dialogues in, and the number of times they were revised. However, the order in which Plato wrote his dialogues is hypothesized based on writing style. His dialogues are therefore organized into three periods: early, middle, and late. Based on writing style, Theaetetus falls in the “late” category, albeit near the beginning. Regardless of what era it was written, Plato never includes himself as a character in the dialogue.