Abstract

In his second period of logical research, which includes several books and treatises, Athir al-Din al-Abhari is the only Avicennan logician who vindicated as invalid one of the two most important Avicennan novelties: iqtirani conditional syllogism. His exposition and reasons for this invalidity in these books and treatises are various and rooted in numerous kinds of conditionals and their truth-conditions and their developments in the books and treatises. His most important reason to deny conditional syllogism is notice to the manifold assumptions used to prove the syllogisms. In this paper, we deal with the main reason, studying the mentioned differences and developments. Citing successor logicians’ points of views on Abhari’s claim and assessment of all of them is out of the purposes of this paper and in need to other researches.