In the late 20th Century, "We have not even a transmuted survival, of that actus: potentia polarity, which was the very life-blood of Scholastic thought, central in its heart and manifest, through its capillaries, at all points of its surface organism."

Whereas the Medieval mind understood as common sense that "Being is potential existence" and that "existence actualizes being"; knew in its heart-of-hearts that "in the universe, actus precedes potentia; for out of potentiality a subject cannot be brought except by a being that is actual"; knew, too, that "the being of God is wholly actual, and is at the same time His existence; but for creatures it is only their existence which actualizes--actualizes not their own being, but the being of God, which they participate; knew that "everywhere around us we must see creatures in a state of potentia being raised to actus" by, paradoxically, an actus which, "behind the appearances," "is already there" (SA 88), we in the modern world know only a world governed by mechanical forces.

The world of actus: potentia is the way the intellectual soul perceives the world.

What is the intellectual soul but the potentiality of determining the species of things? And what are the phenomena themselves? Actually the likenesses or representations of all sorts of 'species"--but potentially (this is, in the condition described as in potentia) immaterial in the soul itself. Phenomena and mind in perpetual interplay, with 'species" hovering somewhere between them as the moment in which the one becomes the other. . . . (SA 88)

See in particular Saving the Appearances, passim.