Abstract

Thomas Aquinas presents a cosmological argument in De ente et essentia. It has been called "the existence argument" because it begins with the existence of things in the world in arguing for the existence of God. Aquinas claims that, because the existence of all things except God is really distinct from their essence, and because nothing but the God of monotheism could cause the existence of things whose essence and existence are really distinct, there must be a God. This argument is widely considered to be fallacious. Some object to Aquinas's argument for the real distinction, interpreted as being based on the cognition of essences. Others criticize Aquinas in his use of "existence" as a property. Still others claim that any argument for God's existence requires the Principle of Sufficient Reason and say that this principle is demonstrably false. ;In this dissertation, I revise this cosmological argument, answering these and other objections to it. First, I advocate an interpretation of Aquinas's argument for the real distinction that is not based on the cognition of essences. Second, I revise this argument and show that the real distinction in all but at most one thing can be demonstrated. Third, I eliminate the controversial argument for the impossibility of an infinite regress of per se causes as essential to this cosmological argument. Fourth, I explain how for Aquinas, "existence" is not a property and I argue that his use of this notion avoids the problems associated with the predication of existence. Fifth, I show how Aquinas does not employ the strong version of the Principle of Sufficient Reason which is demonstrably false, and I explain the grounds that Aquinas does have in claiming that there must be a cause of existence in all but at most one thing. Finally, I argue that this cause must be God as understood in the monotheistic religions by supplementing the argument in De ente et essentia with arguments for divine attributes, and I answer objections to the notion of God's essence being identical to his existence