Being in Act and Being in Potentiality

Aquinas: We exist in potency for certain kinds of change, and when those changes take place, they become actual. Potency for change follows upon the kinds of natures we have, and is something very real about them. Certain realities are subject to potential change in ways that others are not. The physical world is a place where things are actually changing in some respects, but are also subject to potentialchange in other respects. For example, each of us has the potential to learn to think about complex problems in calculus.