knowledge, theories of

Questions about the nature and possibility of knowledge extend throughout Greek philosophy. In the early period, several thinkers raised doubts about our ability to know the truth of the proto-scientific theories they themselves were developing. Plato depicted Socrates as disclaiming knowledge about anything important but searching for fundamental ethical truths. He (Plato) also introduced the idea of unchanging Forms, a grasp of which is crucial for knowledge; in one dialogue, he examined a number of proposed definitions of knowledge itself. Aristotle developed an ideal of scientific knowledge centered on demonstrations of why the objects under examination must have certain features, the starting points of which are an understanding of the essences of the things in question. The Stoics and the Epicureans both offered robustly positive accounts of how knowledge is possible, and they were challenged on this by sceptics of both the Academic and Pyrrhonian traditions.