Is Porphyry’s Isagoge an introduction to Aristotle’s Categories?

Abstract

The present paper is concerned with the famous work of Porphyry, his “Introduction” (Isagoge). During the Middle Ages it was used as a work to start studying philosophy, which partly accounts for its fame. Its subject is quite elementary: it deals with the five basic terms of Aristotelian logic: genus, differentia, species, proprium, accidens; owing to this, it was also known under the title Quinque voces, viz. the five terms. This study concentrates on the problem of Isagoge’s purpose. As it is evident from the title, the treatise was intended to serve as an introduction; nevertheless, the subject to which the introduction was made remains unclear. Some ancient scholars (Boethius among them) made the conjecture that the treatise should be considered an introduction to Aristotle’s Categories. This became widely accepted among the scholars and translators of the text (the Russian edition of it, for instance, bears the title “Introduction to Aristotle’s Categories”), which, however, in itself is no proof that such attribution is correct. Moreover, a closer examination of the text reveals that the assumption about a special affinity between the two works is at least disputable. The author argues that both writings have indeed very little in common in terms of their content: while Aristotelian categories can be described by the medieval term praedicamenta, i.e. the predicates, Porphyry’s five terms under the same system will be called praedicabilia, viz. predicables. In other words, the two books deal with the objects of different logical types, and therefore one of them cannot be considered an introduction to the other. This being the case, it is reasonable to agree with another explanation of Isagoge’s purpose: instead of being an introduction to a specific work, it should be regarded as an introduction to the whole subject of logic.