“The Vision of the Good
Plato’s view of the role of reasoning and inference in human knowledge is embodied in his discussion of two distinct but interrelated methods of seeking the truth: hypothesis and dialectic. In Book VII of the Republic Plato characterizes the method of hypothesis (the “downward way”) as making inferences from widely accepted and possibly true beliefs (such as the axioms of mathematics) without, however, having given an account of these beliefs themselves and therefore without knowing them. The method of dialectic (the “upward way”), by contrast, seeks a first principle beyond these widely accepted beliefs that can be known by giving such an account and from which the widely accepted beliefs themselves will follow as inferences (533b-c). The method of hypothesis thus presupposes the legitimacy of reasoning but leaves open the question of how the premises are to be known. The premises will be refuted if the proposition that follows from them either contradicts the premises or is known independently to be false (the way of elenchus, which follows the argument form modus tollens). If the premises survive refutation, it does not yet follow that they are known. They can be known only if they are inferred from a higher principle that has itself been discovered by the upward way of dialectic.”