From the second half of the fourth century ce until the death of Augustine in 430 Christian theology fully matured. The fact that Marius Victorinus and Augustine wrote in Latin hardly suffices to justify our setting them outside of the dialogue of Christians and pagans within the ancient Greek philosophical world. Even when Latin speakers learned their philosophy from the books of Latin authors like Cicero, what they learned was ancient Greek philosophy. The refined vocabulary of ancient Greek philosophy was the starting point for the expression of theological doctrine. The well-known example of the controversy over how to express the relation between the persons of the Trinity turns upon the understanding of one of the central terms of Greek philosophy – ousia. As theologically motivated students of philosophy learned almost immediately, the Greek philosophers differed in their understanding of ousia. Plato in his Republic has Socrates state that the Good is ‘above’ ousia, primarily owing to the absolute simplicity of the first principle of all. Aristotle in his Metaphysics states that the question ‘what is being?’ is just the question ‘what is ousia?’ He goes on to argue that the primary referent of ousia is the thinking of a divine mind ‘beyond’ which there is nothing. This fundamental disagreement is reflected in the philosophical schools throughout period. So, the question of whether the first person of the Trinity was in any way ‘beyond’ the second and the third is inseparable from the question of whether the first principle must be absolutely simple.