This pair of related ideas goes back to Aristotle and is central to the teaching of Aquinas. I do not question this, but how do I know if I properly understand the teaching?
For example, “Potency and Act divide being in such a way that whatever is, is either pure act, or of necessity it is composed of potency and act as primary and intrinsic principles.”
Mark:
Welcome to CAF. Two great questions. Hopefully, you came to the right place for answers.
Potency and
Act are two words that, as employed by Aquinas, have at least two distinct, yet similar, meanings. Let’s look at
motion first. “Motion” means - in this case - not jiggling around, or rolling on a billiard table, but
essential motion/causation, in other words,
coming-to-be. It helps when defining a word to not merely re-use it in its definition, otherwise, one might define motion as “movement.” That’s wonderful, but it tells us absolutely nothing about - and definitely does not define -
motion. St. Thomas attempts, successfully, I might add, to define “motion” without being tautological. It tells us nothing to say that “motion” is “movement,” or, “motion” is “traveling from point “A” to point “B,”” or “traversing space at light speed.” While such pseudo-definitions are true and useful, they ignore the action that is really taking place.
St. Thomas sees motion (and causation and coming-to-be) as that stage in between the start of a motion and the end of a motion. The beginning of any motion he regards as “
a subject “in potency”” (as it is not yet “in act,” nor is it “acting”). In moving your arm from right to left, for example, it is
in potency on the right and
in act on the left. Your arm is said to be
in act when it has come to the end its action and is fully at rest on the left. These two extremes
represent the extremities of the action, but they have not been used to define “motion.”
Another example is that of an acorn becoming an oak tree. It is said to be
in potency while still an acorn, and
in act, when a grown tree. However, we seem to have left something out of the middle. There was something that took place and we seem to have disregarded it. Some kind of
activity took place. But, “activity” is itself nothing more than another word for “motion.” So, we can’t use that. Instead, understanding that
potency really means that the subject is “not fully actualized in that place yet,” as it would be if it was in Act, but is someplace in the flux
in between. But that is the action of motion which allows St. Thomas to define motion as “
the act of the potential as potential.”
What does that mean? Well, it means that the subject of motion, while still in the
in between, is not in act as to itself (as the subject), but is in the
in between and no longer in
potency - to some greater or lesser extent. But, what
is in act is
precisely the
in-between. The subject can no longer be said to be
in potency, because it has left the gate, but, it cannot be said to be
in act either, because it is not at the finish line. So, the in-between steps up to become a
subject in and of itself. And why not? The action itself has as much right to be a subject of motion as does an arm. It is a reality that, sooner or later, will have Act, and, what is more, is experiencing potency and act, potency and act, all along its trajectory until the end where the primary subject will be, finally, in its own Act.
Once again, remember St. Thomas’s definition: motion is “the act of the potential precisely as potential.” (I have added the word and the underlining to accentuate what he meant.)
That seems straightforward enough until one deals with cases of something moving “from potency to act” and there being more than one kind of potency and more than one kind of act. I don’t know if I’m getting this or kidding myself!
The second kind of
potency - act duet has to do with that which can be said to be
within mobile being. When a rolling billiard ball stops rolling it can be said to be
in potency to be
in act some place else on the poll table, whereupon it will be
in potency again. This does no more than specify current and previous states, and, as you should now be able to see, does not describe “motion” as we did above.
Consider a dog roaming through your yard. It is self-moving from place to place (a form of motion called
local motion). Before the dog enters your yard, it can be said (about the dog) that it is in potency to be in act next to your oak tree. As soon as it is in act next to your oak tree, it may be in potency to be in act in your flower bed. As soon as it is in act in your flower bed, it may be said to be in potency to be in act in your neighbor’s yard. And so on. Thus, the dog is said to “contain” both species of motion’s extremities - the starting point, where it is in potency and the ending point, where it is in act. The dog does not actually
contain those extremities, but it can be represented (in our conception and our speech) as if it contained them, particularly when we are speaking of local motion.
I hope this helps a little. I hope I haven’t made it more confusing. (I’ve got to go to bed now.)
God bless,
jd
If you have more questions please ask them. I know there are better explanations than I’ve given - I know because I’ve read them in this thread! It is an interesting subject which I am trying to reconcile with other ideas that have been recently presented.