Al-Ḫūnaǧī on essentialist and externalist propositions and inferences from the impossible

Afḍal al-Dīn al-Ḫūnaǧī (d. 1248) is one of the most influential Arabic logicians who departed from and argued against Avicenna in various places in his logical works. This paper is about al-Ḫūnaǧī’s account of inferences from the impossible. In this paper, we will overview his formulation of inferences about three main occurrences of impossibility in logic and language: propositions with impossible subjects, syllogism about impossible situations, and implications from a contradictory pair. All these are based on a distinction between two ways of reading the subject term of a proposition which al-Ḫūnaǧī borrowed from Fakhr al-Dīn al-Rāzī, namely the essentialist and the externalist. Later Arabic logicians raised a crucial objection to al-Ḫūnaǧī’s account of the essentialist reading. They argued that all universal propositions are false in this reading. If that is true, many of al-Ḫūnaǧī’s proofs will be trivially valid and redundant. I will argue that the falsity of these propositions does not preclude their truth.