The fallacia consequentis between Term Logic and Sentence Logic in its Medieval Reception

The term ‘consequent’ in ‘fallacy of the consequent’ is nowadays always inter- preted with reference to the rule of modus ponens, most of the time assuming that Aris- totle – the Father of Logic – could not have had anything else in mind. In this article, after briefly recalling how Aristotle deals with this fallacy and the contribution of the Greek commentators on his works, I shall focus on the first period of the reception of the Sophistical Refutations, between the 1160s and the end of the century. I shall exam- ine both the commentaries on Aristotle’s work and the logical handbooks belonging to the Logica Modernorum. On the one hand, in these contexts, the interpretation of the term consequens cannot fail to take into account the meaning assigned to it by Boethi- us in his dialectical and rhetorical works; but, from its first reception on, several alter- native interpretations are advanced, apparently more in tune with Aristotle’s text. In this context, an interpretation emerges which corresponds to modern treatments of the fallacy of the consequent and of its two basic types (Affirming the Consequent and Denying the Antecedent). Third, I shall show how during the thirteenth century this interpretation was commonly adopted, together with the link to Boethius’ locus a com- muniter accidentibus and Aristotle’s reflection on signs proposed in Prior Analytics II 27.