Abstract: In On Invention, Cicero discusses both induction and deduction. In regard to the latter, Cicero presents a controversy between those who advocate a five-part analysis of deductive reasoning and those who prefer three parts. The issue is not practical or pedagogical, but conceptual in nature. Cicero himself prefers analysis into five parts, and rather confusingly he presents the argument of the advocates of five parts as if it were his own. The argument is striking in that it makes elaborate use of mixed hypothetical syllogisms in order to argue for five parts. Cicero claims that the five-part analysis has been preferred by all who take their start from Aristotle and Theophrastus. A survey of what Theophrastus is reported to have said concerning the hypothetical syllogism renders Cicero's claim intelligible. That is not to say that Theophrastus himself advocated a five-part analysis. Most likely the association with him derives from his known interest in hypothetical syllogistic. Later rhetoricians who identified themselves with the Peripatos made the cormection with the founders of the school, thereby gaining authority for a controversial analysis.
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