Rhetoric is the art of discourse, wherein a writer or speaker strives to inform, persuade or motivate particular audiences in specific situations. It can also be in a visual form; as a subject of formal study and a productive civic practice, rhetoric has played a central role in the European tradition. Its best known definition comes from Aristotle, who considers it a counterpart of both logic and politics, and calls it "the faculty of observing in any given case the available means of persuasion." Rhetoric typically provides heuristics for understanding, discovering, and developing arguments for particular situations, such as Aristotle's three persuasive audience appeals, logos, pathos, and ethos. The five canons of rhetoric, which trace the traditional tasks in designing a persuasive speech, were first codified in classical Rome: invention, arrangement, style, memory, and delivery. Along with grammar and logic (or dialectic – see Martianus Capella), rhetoric is one of the three ancient arts of discourse.
Plato sees true rhetoric as psychology which can fulfill its truly “moving” function only if it masters original images [eide]. Thus the true philosophy is rhetoric, and the true rhetoric is philosophy, a philosophy which does not need an “external” rhetoric to convince, and a rhetoric that does not need an “external” content of verity.
Ernesto Grassi, Rhetoric as Philosophy, pp. 31-32 (1980)