Aristotle, and W. Rhys Roberts. Rhetoric. Mineola, NY: Dover, 2004. Kindle Electronic Edition.
Book III, chapter 17.
Aristotle addresses the use of arguments, saying that their duty is to attempt proof. “These proofs must bear directly upon the question in dispute, which must fall under one of four heads. (1) If you maintain that the act was not committed, your main task in court is to prove this. (2) If you maintain that the act did no harm, prove this. If you maintain that (3) the act was less than is alleged, or (4) justified, prove these facts, just as you would prove the act not to have been committed if you were maintaining that” (Aristotle III.17, B. 1417b). A ceremonial speech will normally argue that a deed is noble and useful. A political speech may argue impracticability or injustice (Aristotle III.17, B. 1418a). While Aristotle considers examples appropriate in political discussion, enthymemes are better for forensic debate (Aristotle III.17, B. 1418a). Yet enthymemes must be broken up by narration and maxims.
Aristotle identifies political oratory as challenging due to its focus on the future rather than the past (Aristotle III.17, B. 1418a). Proofs and moral discourse will prove adequate in most positive cases, while enthymeme is more useful in refutation than in positive proofs (Aristotle III.17, B. 1418b).