Avicenna's Views on the Deduction from Two Possible Propositions and Their Relation with Two definitions of Verity- and Actuality-Propositions

In ancient logic, the deductibility of a possible proposition from two possible ones is an enduring controversy confirmed by Aristotle, Ibn-Sina, Fakhr-Al-Din-Al-Razi, Nasir-Al-Din-Al-Toosi and Qutb-Al-Din Al-Razi and disconfirmed by Khunaji, Abhari, Urmavi and Katibi. It is surprising that Modern Logic supports the latter group. On the other hand, it has recently been revealed that the ancient logicians had unconsciously applied the verity- and actuality-propositions equivocally in two meanings, in one of which, the criterion of the division was the relation between the subject and predicate, and in the other, the domain of the universe. By the former criterion, verity-propositions were interpreted by the modal connectives of necessity and possibility; whereas, by the latter criterion, verity-propositions were interpreted by no modal connectives, and actuality propositions were analyzed by the existence predicate. After reporting the related controversies, the present paper translates the opinions, the objections and the defenses into the language of modern logic and shows that the two sides of the controversy do not share the same ideas about the verity- and actuality-propositions. The first group had in mind the first interpretation and the second group the second interpretation.