Possibility of Believing in the Principiality of Existence in Thomas Aquina's Philosophy based on Mulla Sadra's Philosophy

Thomas Aquinas’s system of philosophy is of such undeniable significance to Christian philosophers as is Mulla Sadra’s to Islamic philosophers. What is of prime importance to both of them is the notion of existence, while most western philosophers preceding Aquinas and some of the Islamic philosophers before Mulla Sadra believed in quiddity. Aquinas completely acknowledged the priority of the act of existence to essence, and Mulla Sadra, too, advocated the principiality of existence. In this paper, the authors have tried to explore the possibility of Thomas Aquinas’ belief in the principiality of existence based on Mulla Sadra’s philosophy. They also inquire whether, as claimed by Étienne Gilson and other well-known commentators of Aquinas’ works and ideas, one can consider him to be an advocate of the principiality of existence. This problem is of great significance because, today, Aquinas is a thinker with the greatest number of supporters in the West, where we are witnessing the emergence of new schools of philosophy at all times. Therefore, the study of whether one of the most important interpretations of this thinker’s theories is false might increase the significance of the topic of this research. In doing so, following the library method and given the interpretations and analyses of the contents of the works of these two philosophers, the authors conclude that Aquinas has discussed nothing but the addition of existence to quiddity, which has also been propounded in Ibn Sina’s works. Therefore, he cannot be considered to be a supporter of the principiality of existence in comparison to Mulla Sadra.