This thesis attempts to show that Plotinus and St. Thomas Aquinas differ in their conceptions of God. In particular, I focus upon their understandings of God’s simplicity and their “ontological” claims, i.e., how God relates to being. I claim that their disagreements about God occur because of a metaphysical disagreement on whether being constitutes a composition. Plotinus thinks it does, and assumes that unity is most fundamental, whereas Aquinas thinks it does not, and assumes that being is most fundamental. These different conceptions of being result in different conceptions of God, with Plotinus concluding that the One is beyond being and Aquinas concluding that God is being itself.
Having explained the different conceptions of God advanced by Plotinus and Aquinas, I argue that Plotinus’ position is inferior to Aquinas due to unintelligibility and inconsistency of the One as the source of being and nrelated to being, while also attacking Plotinus’ analogies for it. I also argue that the One is implausible, acting as an empty concept for his beliefs.