rhetorical logic is not logic in the sense that e.g. formal logic or predicate logic is logic.
Rhetorical logic is argument.
Argument involves linking, binding, or associating the facts of the world with claims about the world. Argument is expressed in language. The premises of rhetorical argumentation are supplied by the arguer’s intended audience. An argument properly so called begins with what a community assumes to be the case, or what a community values. In this sense rhetorical argument is dialectical. To argue with someone on the basis of premises that are not their own is no longer dialectic, it is eristic, the sort of partisan discourse that thrills the faithful but fails to reach anyone else.
Here would be an example by way of an excerpt from a comic:
Caption: What, my brothers and sisters, makes an argument rhetorical?
The creepy fairy in the comic excerpt above issues a classic enthymeme, a species of rhetorical argument:
“Let me in,
I’m a fairy”.
In syllogistic terms, “let me in” would be the conclusion, and since whether to let the creepy fairy in is a choice, this argument is deliberative in character. In C.S. Peirce’s rule-case-result terms this would be the result.
The minor premise is “I am a fairy”. In C.S. Peirce’s terms this would be the concrete case.
The major premise in the form of a presupposition would be something like “fairies are wonderful, magical creatures, the sort of creatures that are fun or harmless to let in”, or something like that. In C.S. Peirce’s terms this would the broadly applicable rule. This argument is rhetorical to the degree that the listener accepts in advance the value proposition of the major premise.
The creepy fairy seems to intuit the principle of what makes an argument a rhetorical argument when he asks “don’t you believe in fairies?” The query infers from the major premise, but it also assumes in advance what is probably in dispute, whether the creepy fairy is, in fact, a fairy, which is a species of petitio principii, or begging the question, a logical problem, but not necessarily a rhetorical problem.
The creepy fairy may be creepy, and the primary term of his argument may be suspect on grounds of its origin in folklore, but his conclusion is perfectly rational. Let me explain. For my purposes the rational does not refer to any technique of inferential reasoning. For my purposes you can believe in wood nymphs, water sprites, or vast fairy kingdoms, and be perfectly rational. For my purposes an agent or an agency is rational to the degree that it will hear every side (audi alteram partem). Hence, for me, argument is a rational practice to the degree that it admits of, or will hear, other, or opposing points of view. The fact that the creepy fairy issues an enthymeme suggests persuasion on its face. Persuasion predicates a choice or choices. The listener may open the window to the creepy fairy, or he may not. Choice predicates a decision or decisions, which means developing evaluative criteria to select among options, which means a rational procedure for drawing a conclusion.
The creepy fairy offers his interlocutor in the window a choice, and a reason for the choice, which is the core gesture of any process of deliberation. Whether you take issue with that choice, or its reason, it remains a rational gesture that assumes an agentive auditor (or audience) who can rationally deliberate the choice that was offered based on the reason that was given.
For Aristotle and the peripatetic school of the arts rhetorical, the ars rhetoricae of which this developing blog is but one among many books (or librae, as in liber.rhetoricae), rhetorical argument reduces to but two distinct discursive gestures,
In Aristotle’s own words, the “common pisteis are two in number: paradigm and enthymeme” (Aristotle 179).
Aristotle. On Rhetoric, a Theory of Civic Discourse Trans. George A. Kennedy. New York: Oxford University Press 1991.