Two Senses of Necessity for Avicenna: A Response to a Famous Controversy in Aristotle’s Modal Syllogistic

In Aristotle’s Contributions to Logic, the modal syllogistic has a special place and has been controversial from antiquity to the present. One of the most discussed problems of modal syllogistic is the result of a syllogism composed of an absolute minor and a necessary major. Meanwhile, Aristotle has regarded the result necessary, some of his successors have refuted this conclusion. A recent study to defend the consistency of Aristotle’s modal theory as a whole shows that the proposed counterexamples are not acceptable, referring to the theory of predicable in Topics. Focusing on Avicenna’s work, this study shows that in the logic of Islamic tradition, appealing to the distinction between essential (dhati) and description (wasfi) necessity, another solution has been proposed to this difficulty. A solution that can be used to explain the relation between the Book of Syllogism and the Book of Demonstration. Also, it would solve the ambiguity prevailing in Aristotle’s thoughts.