The problems of the proviso of modal opposition between the contradictory propositions

In this article, we research this issue: The problems of the proviso of modal opposition between the contradictory propositions. Most of the logicians in Islamic world have accepted the modal opposition as a proviso of contradiction between two modal propositions. In their opinion, if two contradictory propositions had a common modality, we should deny either the Law of Non-Contradiction or the Principle of Excluded Middle. So, there is no choice but opposition in “Modality”. In this paper, I want to show that the sameness of modalities has no problem; and contrary to what the logicians thought, it is the modal opposition that leads to deny the Principle of Excluded Middle. From the point of view of this paper, the root of the mistake is confusion between ‘necessity of negation’ and ‘negation of necessity’ (as well as between ‘perpetuity of negation’ and ‘negation of perpetuity’). So, the modal sameness is needed for contradiction, not the modal opposition.