This has its ultimate source in the Rhetoric of Aristotle, who made the following distinction between logic and rhetoric: Logic aims at demonstration by the syllogism and by induction; rhetoric aims at persuasion by the enthymeme and the example. The enthymeme is a rhetorical syllogism, usually with the conclusion or either premise unexpressed. Moreover the premises of an enthymeme are likely to rest on opinion rather than on axioms. The example is a rhetorical induction, usually from fewer cases than are necessary to scientific induction.[[348]]
The same scholastic grouping of logic, rhetoric, and poetic appears in the treatise On the Nature of the Art of Poetry (1647) of the Dutch scholar Vossius, who writes:
As rhetoric is called by Aristotle the counterpart of dialect and that especially because it teaches the manner by which enthymemes may be utilized in communal matters, without a doubt poetic is also to be thought a part of logic, because it discloses the use of examples in fictitious matters.... But rhetoric and poetic seek not only to prove something, but also to delight; they seek not only understanding, but action as well. Wherefore poetic has this in common with rhetoric; that both are the servants of the state.[[349]]
Vossius thus, like Scaliger, makes poetic and rhetoric one in their end to promote desirable action.
How persistent is this rhetorical view of poetry is well illustrated by the Ars Rhetorica of the Jesuit Martin Du Cygne, first published in 1666, and still used as a text-book in Georgetown University. He is discussing the three kinds of argument: syllogism, enthymeme, and example, or induction.
Induction is delightful and is appropriate to an ignorant audience because of its similitudes and examples. This argument is frequently used by rhetoricians and poets, especially Ovid; because it explains attractively and clearly.[[350]]
Thus the grouping of poetic with rhetoric and logic naturally tended to make it partake more and more of the nature of the other two. All of them were taken to be occupied with proving something in an effort to make other people good. They differed only because they used different kinds of proof.
2. The Influence of the Classical Rhetorics
A more explicit influence on the renaissance belief that the function of poetry is to improve social morality is readily seen in the definitions of poetry which have already been quoted from Lombardus and Varchi, who formulated their definitions of poetry by combining Aristotle's definition of tragedy with his definition of rhetoric.[[351]] Another explicit borrowing from classical rhetoric was of Cicero's three-fold aim of the orator: to teach, to delight, to persuade (docere, delectare, permovere).[[352]] Several important Italian critics carried this terminology over into their theories of poetry along with the purpose which has always animated rhetoric--persuasion.
Making Horace a point of departure, Daniello, in 1536, says that the function of the poet is to teach and delight, but more than that--to persuade. He must move his readers to share the emotions of his characters, to shun vice, and embrace virtue.[[353]] This extreme rhetorical parallel was further insisted on by Minturno (1559), who defined the duty of a poet as so to speak in verse as to teach, to delight, and to move.[[354]] And as Aristotle had affirmed in his Rhetoric that the character of the speaker was one of the three essential elements in persuasion,[[355]] Minturno is constrained to make the moral character of the poet an indispensable quality of his poetry. Thus he borrows Cato's definition of the orator as a "good man skilled in public speech" (vir bonus dicendi peritus) from Quintilian,[[356]] and defines the poet as "a good man skilled in speech and imitation" (poeta vir bonus dicendi et imitandi peritus).[[357]]