Historical Development and Pre-Suppositions of the Theory of the Principiality of Existence in Tusi's Analysis

The theory of the principiality of existence or quiddity lacks a systematic model in pre-Sadrian thoughts; however, it is based on certain presuppositions the discovery of which can illuminate Muslim thinkers’ approach to this problem. Khwajah Nasir al-Din Tusi has explained his epistemological ideas regarding these presuppositions. This paper deals with some of the presuppositions underlying the principiality of existence or quiddity as presented by Tusi. Some of them are as follows: 1) the problem of the addition of existence and quiddity and its quality; 2) detecting the relationship between existence and quiddity; 3) the mind or the outside as the place of the realization of this relationship, and 4) evaluating the referents of the mentioned analysis and the realization of quiddity and existence in the outside or emphasizing the exclusive realization of one of them. Through his analyses of each of these presuppositions, Tusi adopts an approach which can represent his agreement or disagreement with the principiality of existence. Accordingly, although the theory of the principiality of existence did not occupy his mind as a problem, his epistemological presuppositions regarding existence and quiddity are consistent with it. The development of the relationship between the ideas of Tusi and Mulla Sadra can be analyzed through explaining the former’s standpoints regarding the above-mentioned presuppositions and his influence over Mulla Sadra.