(CG 2/52). That in Created Subsistent Intelligences there is a Difference be... (Book 2: God The Origin of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

IN whatever being there are found two elements, the one complementary to the other, the proportion of the one element to the other is as the proportion of potential to actual: for nothing is completed except by its own actuality. But in a created intelligent subsistent being there are two elements, the substance itself and the existence thereof which is not the same thing as the substance. Now that existence is the complement of the existing substance: for everything actually exists by having existence. It follows that in every one of the aforesaid substances there is a composition of actuality and potentiality.

2. What is in any being, and comes of the agent that produced it, must be the actuality of that being: for it is an agent's function to make a thing be in actuality. But, as shown above (Chap. XV), all other substances have their existence of the prime agent: indeed their being created substances consists precisely in this, that they have their existence of another. Existence itself therefore is in these created substances as a sort of actualisation of the same. But that in which actuality is received is potentiality: for actuality is such in relation to potentiality. In every created subsistent being therefore there is potentiality and actuality.