Persuasion, according to Aristotle and the many authorities that would echo him, is brought about through three kinds of proof (pistis) or persuasive appeal:

Although they can be analyzed separately, these three appeals work together in combination toward persuasive ends.

Aristotle calls these "artistic" or "intrinsic" proofs—those that could be found by means of the art of rhetoric—in contrast to "nonartistic" or "extrinsic" proofs such as witnesses or contracts that are simply used by the speaker, not found through rhetoric.

Sources: Arist. Rhet. 1.2.2-3