Socrates asks,

Must not the art of rhetoric, taken as a whole, be a kind of influencing of the mind by means of words, not only in courts of law and other public gatherings, but in private places also? And must it not be the same art that is concerned with great issues and small, its right employment commanding no more respect when dealing with important matters than with unimportant? Phaedrus, 261a-261b.

But since we have the ability to persuade one another and to make dear to ourselves what we want, not only do we avoid living like animals, but we have come together, built cities, made laws, and invented arts. Speech is responsible for nearly all our inventions. It legislated in matters of justice and injustice and beauty and baseness, and without these laws, we could not live with one another. By it we refute the bad and praise the good; through it, we educate the ignorant and recognize the intelligent. We regard speaking well to be the clearest sign of a good mind, which it requires, and truthful, lawful, and just speech we consider the image of a good and faithful soul. With speech we fight over contentious matters, and we investigate the unknown. We use the same arguments by which we persuade others in our own deliberations; we call those able to speak in a crowd "rhetorical"; we regard as sound advisers those who debate with themselves most skillfully about public affairs. If one must summarize the power of discourse, we will discover that nothing done prudently occurs without speech, that speech is the leader of all thoughts and actions, and that the most intelligent people use it most of all.

Let rhetoric be [defined as] an ability, in each [particular] case, to see the available means of persuasion. This is the function of no other art; for each of the others is instructive and persuasive about its own subject: for example, medicine about health and disease and geometry about the properties of magnitudes and arithmetic about numbers and similarly in the case of the other arts and sciences. But rhetoric seems to be able to observe the persuasive about "the given," so to speak. That, too, is why we say it does not include technical knowledge of any particular, defined genus [of subjects].

The task of the public speaker is to discuss capably those matters which law and custom have fixed for the uses of citizenship, and to secure as far as possible the agreement of his hearers.

There is a scientific system of politics which includes many important departments. One of these departments—a large and important one—is eloquence based on the rules of art, which they call rhetoric. For I do not agree with those who think that political science has no need for eloquence, and I violently disagree with those who think that it is wholly comprehended in the power and skill of the rhetorician. Therefore we will classify oratorical ability as a part of political science. The function of eloquence seems to be to speak in a manner suited to persuade an audience, the end is to persuade by speech.

What is called "rhetorical," as a means of conscious art, had been active as a means of unconscious art in language and its development, indeed, that the rhetorical is a further development, guided by the clear light of the understanding, of the artistic means which are already found in language. There is obviously no unrhetorical "naturalness" of language to which one could appeal; language itself is the result of purely rhetorical arts. The power to discover and to make operative that which works and impresses, with respect to each thing, a power which Aristotle calls rhetoric, is, at the same time, the essence of language; the latter is based just as little as rhetoric is upon that which is true, upon the essence of things. Friedrich Nietzsche on Rhetoric and Language, p 21.

[Rhetoric is] the political effectivity of trope and argument in culture. Such a working definition includes the two traditional meanings of rhetoric—figurative language and persuasive action—and permits me to emphasize either or both senses, differently in different discourse at different historical moments, in order to specify more exactly how texts affect their audiences in terms of particular power relations. Rhetorical Power.

The study of how people use language and other symbols to realize human goals and carry out human activities [. . .] ultimately a practical study offering people great control over their symbolic activity. Shaping Written Knowledge, p. 6.

[The problem is bringing] rhetoric, the orator, the struggle of discourse within the field of analysis; not to do, as linguists do, a systematic analysis of rhetorical procedures, but to study discourse, even the discourse of truth, as rhetorical procedures, as ways of conquering, of producing events, of producing decisions, of producing battles, of producing victories. In order to "rhetoricize" philosophy.

Rhetoric is the mobilization of signs for the articulation of identities, ideologies, consciousnesses, communities, publics, and cultures. 

But as Kenneth Burke has taught us, rhetoric may be defined very broadly (e.g., I tell the students in my undergraduate rhetorical theory class that the study of rhetoric is the study of how we use language and how language uses us).

What rhetoric has always addressed: not the mastery and regulation of language so much as the ways in which language shapes, reflects, and changes practices among members of particular communities.

In antiquity rhetoric was education, the leading out of the child from the private world of the family (and the family's responsibility for suitable training) to the social and political worlds. Learning to write well, which meant, on the one hand, a complicated technique, and, on the other hand, a discrete (primarily literary) body of knowledge, was the necessary preparation for what was seen as the only truly human existence: that of a participant in the social life of the community and the political life of the state.

[Rhetoric] deals with "questions surrounding any study of language: the relation between language and the world, the relation between discourse and knowledge, the heuristic and communicative functions of verbal expression, the roles of situation and audience in shaping utterance, the social and ethical aspects of discourse. . . .

Rhetoric is the art of describing reality through language. Under this definition, the study of rhetoric becomes an effort to understand how humans, in various capacities and in a variety of situations, describe reality through language. To act rhetorically is to use language in asserting or seeming to assert claims about reality. At the heart of this definition is the assumption that what renders discourse potentially persuasive is that a rhetor (e.g. a speaker or writer) implicitly or explicitly sets forth claims that either differ from or cohere with views of reality held by audiences (e.g. a specific scholarly community, a reader of fiction, or an assembly of persons attending a political rally). Communication and Knowledge: An Investigation in Rhetorical Epistemology. 62.

Law is most usefully seen not, as it usually seen by academics and philosophers, as a system of rules, but as a branch of rhetoric, and . . . the kind of rhetoric of which law is a species is most usefully seen not, as rhetoric usually is either as failed science or as the ignoble art of persuasion, but as the central art by which community and culture are established, maintained, and transformed. So regarded, rhetoric is continuous with law, and like it, has justice as its ultimate aim. Law as Rhetoric, Rhetoric as Law: The Arts of Cultural and Communal Life, 52.

Rhetoric, which was the received form of critical analysis all the way from ancient society to the 18th century, examined the way discourse are constructed in order to achieve certain effects. It was not worried about whether its objects of inquiry were speaking or writing, poetry or philosophy, fiction or historiography: its horizon was nothing less than the field of discursive practices in society as a whole, and its particular interest lay in grasping such practices as forms of power and performance. This is not to say that it ignored the truth-value of the discourse in question, since this could often be crucially relevant to the kinds of effect they produced in their readers and listeners. Rhetoric in its major phase was neither a language, nor a "formalism," preoccupied simply with analyzing linguistic devices. It looked at such devices in terms of concrete performance-they were means of pleading, persuading, inciting and so on-and at people’s responses to discourse in terms of linguistic structures and the material situations in which they functioned. It saw speaking and writing not merely as textual objects, to be aesthetically contemplated or endlessly deconstructed, but as forms of activity inseparable from the wider social relations between writers and readers, orators and audiences, and as largely unintelligible outside the social purposes and conditions in which they were embedded.

The rhetoric under discussion here is that metalanguage (whose language-object was "discourse") prevalent in the West from the fifth century BC to the nineteenth century AD. We shall not deal with more remote efforts (India, Islam), and with regard to the West itself, we shall limit ourselves to Athens, Rome, and France. This metalanguage (discourse on discourse) has involved several practices, simultaneously or successively present, according to periods, within "Rhetoric ":

1. A technique, i.e., an "art," in the classical sense of the word; the art of persuasion, a body of rules and recipes whose implementation makes it possible to convince the hearer of the discourse (and later the reader of the work), even if what he is to be convinced of is " false."
   
   
2. A teaching: the art of rhetoric, initially transmitted by personal means (a rhetor and his disciples, his clients), was soon introduced into institutions of learning; in schools, it formed the essential matter of what would today be called higher education; it was transformed into material for examination (exercises, lessons, tests).
   
   
3. A science, or in any case a proto-science, i.e. a. a field of autonomous observation delimiting certain homogeneous phenomena, to wit the "effects" of language; b. a classification of these phenomena (whose best-known trace is the list of rhetorical "figures"; c. an "operation" in Hjelmslevian sense, i.e. a meta-language, a body of rhetorical treatises whose substance—or signified—is a language-object (argumentative language and "figured" language).
   
   
4. An ethic: as a system of "rules," rhetoric is imbued with the ambiguity of that word: it is at once a manual of recipes, inspired by a practical goal, and a Code, a body of ethical prescriptions whose role is to supervise (i.e. to permit and to limit) the "deviations" of emotive language.
   
   
5. A social practice: Rhetoric is that privileged technique (since one must pay in order to acquire it) which permits the ruling classes gain ownership of speech. Language being a power, selective rules of access to this power have been decreed, constituting it as a pseudo-science, closed to "those who do not know how to speak" and requiring an expensive initiation: born 2500 years ago in legal cases concerning property, rhetoric was exhausted and died in the "rhetoric " class, the initiatory ratification of bourgeois culture.
   
   
6. A ludic practice: since all these practices constituted a formidable ("repressive," we now say) institutional system, it was only natural that a mockery of rhetoric should develop, a "black" rhetoric (suspicions, contempt, ironies): games, parodies, erotic or obscene allusions, classroom jokes, a whole schoolboy practice (which still remains to be explored, moreover, and to be constituted as a cultural code)."The Old Rhetoric: An aide-mémoire." The Semiotic Challenge, 12-14.

What happens, then, if we choose to begin with our knowledge that we are essentially creatures made in symbolic exchange, created in the process of sharing intentions, values, meanings, in fact more like each other than different, more valuable in our commonality than in our idiosyncrasies: not, in fact, anything at all when considered separately from our relations? What happens if we think of ourselves as essentially participants in a field or process or mode of being persons together? If man is essentially a rhetorical animal, in the sense that his nature is discovered and lived only in symbolic process, then the whole world shifts: even the usage of words like I, my, mine, self, must be reconsidered, because the borderlines between the self and the other have either disappeared or shifted sharply . . . All we need do is honour what we know about who we are and how we come to be, in language. Once we give up the limiting notions of language and knowledge willed to us by scientism, we can no longer consider adequate any notion of "language as a means of communication" . . . It is, in recent models, the medium in which selves grow, the social invention through which we make each other and the structures that are our world, the shared product of our efforts to cope with experience.

Rhetoric has a number of overlapping meanings: the practice of oratory; the study of the strategies of effective oratory; the use of language, written or spoken, to inform or persuade; the study of the persuasive effects of language; the study of the relation between language and knowledge; the classification and use of tropes and figures; and, of course, the use of empty promises and half-truths as a form of propaganda. Nor does this list exhaust the definitions that might be given. Rhetoric is a complex discipline with a long history: It is less helpful to try to define it once and for all than to look at the many definitions it has accumulated over the years and to attempt to understand how each arose and how each still inhabits and shapes the field. Patricia Bizzell and Bruce Herzberg, "General Introduction." The Rhetorical Tradition: Readings from Classical Times to the Present. p 1.