Pr ecis of Aristotle’s Modal Syllogistic

Aristotle was the founder of modal logic. In his Prior Analytics, he developed a complex system of modal syllogistic. While influential, this system has been disputed since antiquity and is today widely regarded as incoherent or inconsistent. In view of this, Aristotle’s Modal Syllogistic explores the prospects for understanding the modal syllogistic as a coherent and consistent system of modal logic. To this end, I introduce a model that matches all of Aristotle’s claims about the validity and invalidity of modal syllogisms. This model is developed throughout the book and is summarized in Appendix B. The model shows that, contrary to what is often thought, the set of those claims is consistent. Moreover, the purpose of the book is to explain, as far as possible, why Aristotle made the claims he made in the modal syllogistic. Thus, my aim is to give an account of Aristotle’s grounds for judging a given modal syllogism valid or invalid. The book consists of three parts. The first deals with Aristotle’s assertoric, or non-modal, syllogistic (Prior Analytics 1.1–2 and 4–7). The second part deals with the apodeictic syllogistic, in which Aristotle discusses necessity propositions (Prior Analytics 1.3 and 8–12). The third part deals with the problematic syllogistic, in which Aristotle discusses possibility propositions (Prior Analytics 1.3 and 13–22). In what follows, I give an overview of each of these three parts.