Rhetoric (from Greek ρητωρ, rhêtôr, "orator") is one of the three original liberal arts or trivium (the other members are dialectic and grammar). While it has meant many different things during its 2500-year history, it is generally described today as the art of persuasion through language.
Plato is the great historical enemy of the sophistic movement. For Plato, the essence of philosophy lay in the process of dialectic, in which reason and discussion progressively lead to the discovery of important truths. Plato believed that the sophists cared not for the truth of an argument, but only how they might appear to win it.
Two of Plato's dialogues are especially focused upon rhetoric. The Gorgias emphasizes Plato's contention that the sophists value style over substance. Philosophy and rhetoric are related in the same way as are medicine and cosmetics. That is, medicine (like philosophy) is concerned with what is truly best for its subjects, whereas cosmetics (like rhetoric) is concerned solely with appearances. The Phaedrus was written after the Gorgias. While it continues Plato's critique of rhetoric, he also holds out the possibility that a rhetoric may yet be devised which is true and noble.
In fact, the rhetoric developed by Plato's student, Aristotle, can be seen as just such a rhetoric. In the first sentence of The Art of Rhetoric, Aristotle describes rhetoric as the counterpart of dialectic. By this, he means that, while dialectical methods are necessary to find truth, rhetorical methods are required to communicate it.
Aristotle defined rhetoric as "the faculty of observing in any given case the available means of persuasion." With this definition Aristotle placed invention, or the discovery of lines of argument, at the very center of the rhetorical enterprise. In doing so he set his system apart from that of the sophists, which focused on outcomes of public speaking. For Aristotle, then, rhetoric is an architectonic, rather than a productive, art.
Aristotle's systematic description of rhetoric completely dominated rhetorical thought through the middle ages and beyond. His chief emphasis is upon the three kinds of proof that can be offered on behalf of an argument. Logos consists of the use of language in constructing an argument. Pathos concerns emotional appeals. Ethos focuses upon how the character of a speaker influences an audience to consider him to be believable.
Also very important in Aristolte's scheme are Kairos, the context in which the proof will be delivered, The Audience, the psychological and emotional makeup of those who will receive the proof, and To Prepon, the style with which he clothes his proof. In order for rhetoric to be effective, the orator must be sensitive to these elements. He must realize that the context will constrict what he can say and what will be considered relevant. He must attune his message to his audience, or he will risk alienating or disgusting his audience. And he must embody his ideas in a way that is both proper to the occasion and to his audience. For example, the orator would not use colloquial or slang language if he was speaking about a lofty topic. Indeed, all three elements are intertwined: The character of the audience will define how the orator judges the context, the context will define the style he will use, and, through the experimentation, the style will influence what the context consists of.
While Western philosophy has tended to emphasize Logos, Aristotle's three bases of evidence provide a philosophical foundation for the broadly conceived psycho-social or behavioral sciences where accounting for non-rational factors in human behavior is necessary for explanatory completeness. Especially professions or occupations in applied social sciences, such as psychotherapy are based in the practice of persuasion, or rhetoric in Aristotle's broad conception.
The Romans were great borrowers, and they found much value in Aristotle's rhetoric. Cicero and Quintilian were chief among Roman rhetoricians, and their work is clearly an extension of Aristotle's. In particular, Quintilian codified rhetorical studies under five canons that would persist for centuries in academic circles. Inventio (invention) is the process that leads to the development and refinement of an argument. Once an argument is developed, it is up to dispositio (disposition, or arrangement) to determine how it should be organized for greatest effect. Once the speech content is known and the structure is determined, the next steps involve pronuntiatio (language choice) and elocutio (delivery). Finally, memoria (memory) comes to play as the speaker recalls each of these elements during the speech.
In the 16th century, after long domination by Scholasticism and Aristotelian thinking, Petrus Ramus proposed to reorganize the school curriculum of the day. Breaking with the traditional divisions of the liberal arts, he proposed something similar to the contemporary division of universities into multiple schools and departments of study (in fact, Ramus is the ultimate source of this organizational scheme). His efforts succeeded. The five components of rhetoric no longer lived under the common heading of rhetoric. Instead, invention and disposition were determined to fall under the heading of philosophy, while language, delivery, and memory were all that remained for rhetoric.
Once stripped of its more substantial elements, rhetoric became a much less prestigious topic of study. Much as Plato originally condemned the rhetoric of the sophists for its lack of concern for truth, rhetoric now came to be associated with emptiness: it ceased to be connected with ideas. In popular use, this connotation persists to this day. However, the term is still used in a deeper and more constructive sense in the study of human communication.
(Definitions, discussion of conflicting opinions, ending with synthesis: a working general definition of rhetoric for this article)