The definition of Imamate serves as the foundation of Imamate studies. Within the Shiite thoughts, a systematic as well as reasonable definition of Imamate was for the first time put forward by the theologians in Bagdad School. In the present study, the researcher has investigated the definition of Imamate from the viewpoint of the most eminent theologians in Bagdad School. He has also dealt with the traits of these definitions along with their relation to the concepts of Prophethood and apostleship through the eyes of the theologians in Bagdad School, while elaborating on the differences among them. And finally, he has conducted a general evaluation of the Bagdad Schools’ approach to defining Imamate. In researcher’s view, the approach of Bagdad School’s theologians to defining Imamate is methodologically acceptable; however, it is problematic in terms of content and comprehensiveness as well as its conformity to traditional and Quranic teachings in relation to Imamate. Accordingly, Imamate needs to be completely defined and likewise redefined. And this should be accomplished with respect to the position of Imamate in the Quran and traditions as well as the related concepts of Imamate employed in the Shiite thought
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