Epistemology

Socrates (c. 470–399 B.C.E.), as portrayed in numerous dialogues of Plato (c. 428–348/347 B.C.E.), is famous for professing his ignorance. He does not say, as often claimed, that he knows he knows nothing, but that he knows he knows nothing truly valuable. How, then, does Socrates conceive the truly valuable knowledge that he lacks? A plausible answer is that it is knowledge of the nature of the human virtues—knowledge that, if one possessed it comprehensively, would amount to a quite general grasp of how to live our lives. In some of the same dialogues, Socrates also proposes a principle that has been called the Priority of Definition: unless one can provide a definition of a thing—unless one can specify what it is—one is in no position to say anything authoritative about that thing. It is difficult to see how inquiry can proceed if this principle is fully adopted, a problem that Plato has Socrates face in the Meno. Socrates' answer is the Pythagorean-influenced doctrine that "learning is recollection." We all have lived many past lives, and have knowledge buried within us; the trick is to reactivate this knowledge or bring it to the surface. The same dialogue also includes an account of the difference between knowledge and opinion; knowledge involves an ability to explain why things are as they are. Knowledge (or epistêmê, one of the words regularly translated "knowledge") thus seems to be a kind of systematic understanding of some subject-matter, as opposed to the mere awareness of isolated facts designated by the term "opinion."

The idea that learning is recollection recurs in other works of Plato, but in conjunction with the notion of separate, purely intelligible Forms. How exactly Plato conceives of Forms, and the motivations he has for postulating them, are controversial. But it is clear that each Form is thought of as encapsulating the being, or the essence, of the quality of which it is the Form; the Form of Beauty, for example, is the true nature of beauty, which particular beautiful objects in the world around us exemplify only in a limited or partial way. It is emphasized in the Republic that genuine knowledge is restricted to those who have a grasp of the Forms; anyone whose experience is limited to the everyday sensory world is only capable of opinion. To grasp Forms requires lengthy training, focused on minimizing one's reliance on the senses; a central tool in this process is pure mathematics.

The one dialogue of Plato devoted specifically to the question "What is knowledge?" is the Theaetetus; but this, though probably a mature work, surprisingly contains no mention of Forms whatever. The three definitions of knowledge considered are "Knowledge is perception," "Knowledge is true judgment," and "Knowledge is true judgment plus an account." While all three definitions are rejected, the third seems to come closest to success; and this interestingly resembles the picture of knowledge as appropriately justified true belief, favored by many contemporary epistemologists.