Cicero, On Invention 1.51-77: Hypothetical Syllogistic and the Early Peripatetics

In the course of this paper, I shall say some things about Cicero’s discussion of induction, but my primary concern will be with his account of deduction. In particular, I want to call attention to Cicero’s argument for a quinquepartite analysis of deductive reasoning (Ded. 3). It is remarkable in that it makes elaborate use of the mixed hypothetical syllogism, and also of some importance in that it supplements our evidence for early Peripatetic interest in syllogisms of this land. Recent scholarship on the history of ancient logic has generally focused on later sources—like Alexander of Aphrodisias, Boethius, Philoponus and Simplicius— and pointed to Theophrastus as a significant contributor to the development of hypothetical syllogistic. Cicero, writing three centuries before Alexander, seems not only to confirm the importance of Theophrastus but also to indicate that his contributions were recognized as such by Hellenistic rhetoricians. In presenting this thesis, I shall not be accepting Cicero’s claim to have written more accurately and diligently than others (Ded. 7), but I will suggest that the argument in favor of quinquepaitite analysis (Ded. 3) is more coherent than what precedes (Ded. 2) and that this difference is largely attributable to Cicero’s use of sources