Plato:  Rhetoric is "the art of winning the soul by discourse."

Aristotle: Rhetoric is "the faculty of discovering in any particular case all of the available means of persuasion."

Cicero:  "Rhetoric is one great art comprised of five lesser arts: inventio, dispositio, elocutio, memoria, and pronunciatio."  Rhetoric is "speech designed to persuade."

Quintillian:  "Rhetoric is the art of speaking well."

Francis Bacon: The duty and office of rhetoric is to apply reason to imagination for the better moving of the will.

George Campbell:  [Rhetoric] is that art or talent by which discourse is adapted to its end.  The four ends of discourse are to enlighten the understanding, please the imagination, move the passion, and influence the will.

I. A. Richards:  Rhetoric is the study of misunderstandings and their remedies.

Richard Weaver:  Rhetoric is that "which creates an informed appetition for the good."

Erika Lindemann:  "Rhetoric is a form of reasoning about probabilities, based on assumptions people share as members of a community."

Philip Johnson: "Rhetoric is the art of framing an argument so that it can be appreciated by an audience."

Andrea Lunsford:  "Rhetoric is the art, practice, and study of human communication."