Gerhard Johann Vossius on the Definition of Rhetoric and Its Three Types
Elementa Rhetorica (Cellis, 1662).
Rhetoric, which in Latin is called oratory gets its name from the Greek word ῥέω, that is, to flow. [Hence, it is the power or art of using language fluently.] Just as grammar shows us the way of conversing well or purely, so Rhetoric teaches us to speak well or to converse prudently, copiously, and ornately. Rhetoric is defined as “the skill of discovering in any subject-matter, what in it is suitable for persuading.” Therefore, the ultimate end of the orator is to persuade. His or her duty is to see what conduces to persuasion or to speak what is fitting to persuade. Its material is anything, though especially civil/public questions.
The question is either a thesis or a hypothesis. A thesis is general or universal in nature. Such as: “Whether it is permissible to kill someone lying in ambush?” A hypothesis is a particular or singular question like “Whether Milo justly killed Clodius?
The Orator must do these four things: find arguments, arrange those discoveries, furnish that arrangement well, and convey those furnishings. And for each of these duties, we get the parts of rhetoric: invention, disposition, elocution, and delivery.
Invention is the devising of arguments which are fit to persuade. Arguments are threefold: Customs, reasons, or affections, which the Greeks call logos, ethos, and pathos. Reasons have the power to teach, customs to unite, and affections to stir up.
Arguments of the first type are either artificial or inartificial. Those which are called artificial are those found by the orator with the benefit of an art. They vary on account of the kinds of hypotheses, which the Latins call causes [or reasons].
There are three kinds of reasons: Demonstrative, deliberative, and juridical.
The Demonstrative is when we praise or blame. And this principally has to do with present time. Praise and blame of everything is either of persons, facts, or things.
Of persons, as if you were to praise Cicero and blame Antony.
Of facts, as if you were to praise the willingness of Marcus Regulus to return to his enemies; or if you were to find fault in Cato the Younger, because he took things into his own hands, lest they fall into the power of Julius Ceasar.
Of things, as if you were to praise eloquence, or agriculture. Or if you were to blame the vice of an ungrateful soul.
Arguments of this kind are chiefly sought from an honorable or base thing.
The deliberative kind of cause is when we attempt to persuade or dissuade. Like if you try to persuade for peace or a truce; to dissuade against going to war or the contrary.
Every deliberation concerns future things. And principally what is considered in deliberation is whether something is useful or useless.
The juridical kind is when we accuse or defend. In this way, Milo, attempting to kill Claudius, was accused by the friends of Claudius, but defended by Cicero. This kind of cause treats of past things.