ABSTRACT
Avicenna's originality is evident in his unorthodox treatment of the semantics of assertoric propositions, in his systematization of the logic of ampliated modal propositions, and in his sketches towards a logic of those modal propositions that are qualified with phrases such as 'so long as'. This chapter focuses on the work of scholars such as Street who have worked with Avicenna's texts in the original languages. Avicenna analyses universal assertoric propositions in an unconventional way, modalizing both subject and predicate. The chapter examines Avicenna's account of substantial propositions first, then his account of descriptionals. In other respects Avicenna's account of assertoric syllogistic is orthodox, retaining the standard first- and third-figure moods. Avicenna's discussion of syllogisms with descriptional premises begins with a reference to Theophrastus's peiorem rule, in so far as it relates to the modality of the premises and conclusion.
