An introduction to metaphysics is in order. When we speak of metaphysics, we are not speaking of the odd, occultic section of the used bookstore. Instead, we are speaking of the branch of philosophy that studies how things exist.
Thomas Aquinas wrote what is arguably the pinnacle of the expression of metaphysics as it applies to God. Let us examine a statement of metaphysics and try to explain it.
Potency and act divide being in such a way that whatever is, is either pure act or of necessity composed of potency and act.
No doubt such a statement appears gibberish to the common ear. To understand such a statement, we must explain the terms.
The terms potency and act are old ways of saying potential and actual. A man is potentially strong, then he exercises and lifts weights and becomes actually strong.
In metaphysics, the term being has more than one sense.
- A being is a thing, in the sense of a human being. In this sense, being is a noun.
- Being is an action, in grammar a participle, such as running, jumping, sewing, or hitting. Just as running is the action of one who runs, being is the action of one who exists.
In English, the two senses of being can be easily confused. Many of the original writings about metaphysics were in other languages, where the two senses are different words. Latin speaks of ens, being as a noun or thing, and esse, being as a participle or action.
We get more confused when we realize that the noun being (ens), must necessarily include the act of being (esse). A thing must exist to be a thing, therefore whatever exists includes the act of existing.
So our sentence above might be rewritten in terms that makes more sense to us:
Potential and actual divide things that exist in such a way that whatever exists, is either purely actual or of necessity composed of potential and actual.
This statement is significant. Whatever is purely actual, with no mixture of potential, cannot get better, or stronger, or change in any way. A purely strong man could not do anything to get stronger. If he could potentially get stronger, then he would have potential that has not been actualized and his strength would not be purely actual. A man who could get stronger is composed of potential and actual. All composed things are limited, for they have not yet actualized their potential.
So, to repeat, if a thing were fully actualized, it would have no potential to get better, stronger, wiser, or any other way. If a thing is composed of potential and actual, it has some strength or some wisdom, but has the potential to get stronger or wiser.
So the statement above is saying that whatever exists is either purely actual, in which case it cannot increase in any way, or is a mixture of potential and actual.
Why does this matter? Because everything we observe in this world is a mixture of potential and actual. Everything could get warmer, or denser, or stronger, or wiser. Everything that is a mixture of potential and actual was caused to be that way, and could not have caused itself. Therefore there must be a thing which is purely actual, with no mixture of potential. This thing that is purely actual, therefore necessarily exists, and this we call God.
But this concept of potential and actual has more applications. When humans think a thought, we move from potentially thinking to actually thinking. Only something that is already actual can cause something to change from potentially existing to actually existing. Since we have some things about us that are actual, it is logical that we can cause potentials to become actual. For example, if we are potentially strong, we can do exercise and become actually stronger.
Therefore this concept of act and potency supports the existence of God and human free will agency.