In his proofs of Le- and Ae-conversion in Logic for Shams al-Dīn, Najm al-Dīn al-Kātibī (d. 1276/7) accepts syllogisms that have redundant premises as theses. Similarities in Avicenna’s and Kātibī’s doctrines of the per impossibilesyllogism suggest that Avicenna could have adopted such proofs and remained consistent with the principles of his syllogistic. However, analysis of their modal syllogistic and their ideas about the nature of implication (luzūm) reveals that Avicenna could not employ the type of per impossibile syllogism that Kātibī does and remain faithful to his modal theory, or to the Aristotelian vision of the theory of syllogistic as a theory of reasoning. In his commentary on Afḍal al-Dīn al-Khūnajī’s (d. 1248) Disclosure of Secrets Kātibī offers a second analysis of per impossibile syllogisms. Kātibī envisions a generic sense of logical necessitation that accommodates the sense in which an antecedent implies a consequent and premises imply a conclusion. This evidence may explain why Kātibī admitted redundantly concluding syllogisms as theses. If Avicenna was committed to a strict distinction between these senses, this may partially account for why Avicenna does not adopt Kātibī’s unusual syllogisms.
|Journal||Oriens: journal of the International Society for Oriental Research|
|Publication status||Published - 2015|
- per impossible syllogism
- qiyas al-khalf