Ma`rifat Falsafi

Stating various types of composition of conjunctive and disjunctive conditional propositions from elements such as categorical and conditional propositions in chapter 8, section 3 of his book “ Al Isharat wa al Tanbihat” , Ibn Sina gives several examples the first of which is the conjunctive proposition composed of a conjunctive and a disjunctive proposition. This very example is the core of a noteworthy controversy between two commentators of this book i.e. Khajeh Nasir al Din Al Tusi and Fakhr Razi. Fakhr Razi holds that any cogent conjunctive proposition is equivalent to only one exclusive disjunctive proposition, a view somewhat identical with what is raised in modern logic. In contrast, Khajeh Tusi believes that this exclusiveness is not right and any cogent conjunctive proposition can be reduced to an inclusive disjunctive proposition or incompatible disjunctive one without distinction or preference. Judging the views of Fakhr Razi and Khajeh Tusi and explaining the view of modern logic in this regard, the present article benefits from modern logic. Finally, explaining the difference between the view of Fakhr Razi and modern logic, it concludes that the right view is that of Khajeh Tusi confirmed by modern logic.