Abstract

Philosophers speculations embrace many arguments for knowledge of God. These methods of cognition, from a particular point of view, have been logically classified under" a priori' and * a posteriori.' ones.Here the author has tried to expound, what it is well-known as the argument of righteous ones, as the a priori argument; and yet we are better to call this argument as "ontological argument".In this article, the ontological arguments, such as those of Saint Anselm, Descartes, Leibniz, and Kant's critique on the ontological argument and critique on Kant's doctrine, as well as, ontological argument in Islamic philosophy are interjected. Finally, the main elements of Mulla Sadra's doctrine are reported as follows:"In processing this argument, Mulla Sadra employs a number of his other ontological doctrines, among which the principiality of existence, the gradational unity of the existence, and possibility by way of dependence are most prominent ones, from which the conspicuous character of his ontological originates.