عنوان مقاله [English]
To Avicenna, the relation between the subject and the predicate is of three kinds: possibility, necessity, and impossibility. Impossibility is the same as necessary non-existence. The word ‘modal’ in modal logic refers to these three. Avicenna has dealt with different types of modal propositions in his logic books. However, in his philosophical books he has limited himself to propositions with the predicate of existence. In a merely structural division, based on the predicate of propositions, there are logical necessity and philosophical necessity. If necessity is not looked upon from a structural viewpoint, there would still be two types of necessity. Logical necessity based on the principle of contradiction. Predicates which have this property are the essentials in the Isagoge. In addition to these, Avicenna considers the ‘required essential accidents’, from Borhan, as necessary. But he does not base them on the principle of contradiction. I’d like to call them ‘philosophical’, whose other criteria is not the principle of Identity or contraction. Avicenna labels the essential accident as ‘required’ and considers them necessary. The necessity of the ‘required’, however, does not need ‘persistence’ or the principle of contradiction.