Aristotle’s Definition of Motion

I’ve been thinking for a long time that I should stop trying so hard to write completely finished, polished articles, but then I always end up working too hard on whatever idea I come up with. So this is going to be my first attempt at posting more often but trying less hard.

I’ve been struggling to understand Aristotle’s definition of motion for a long time now. “Motion,” in Aristotle’s terminology, refers to any sort of change as it is taking place; in other words, it refers to the process of change rather than the fact of change.

So how do we define motion? The most obvious prima facie definition is “change spread out over time.” But this is problematic because Aristotle wants to define time in terms of motion. Aristotle’s definition of time is “the numerical measure of motion according to the before and after.” Time arises from motion, not vice-versa.

Another apparently tempting definition is “the transition from potency to act.” But this is a circular definition; “transition” basically means “motion.” All this definition tells us is that motion starts with potency and ends with act. It doesn’t tell us what motion actually is.

The definition that Aristotle finally arrives at is:

Motion is the act of a potency insofar as it is potency.

The good part of this definition is that it defines motion solely in terms of concepts that are more basic than motion. It makes no reference to time, nor does it rely on any synonym of “change,” “transition,” etc. The only concepts it uses are act and potency, pretty much the most basic concepts in existence.

But the problem is that it looks like a blatant contradiction. How can there be an act of a potency? Something in act, by definition, is no longer in potency, and something in potency, by definition, is not yet in act.

Aristotle also gives an illustration of the definition that shows clearly that he means exactly what he sounds like he means. He says that if the definition of “to be potentially a statue” and that of “to be bronze” were the same, then to be bronze would simply be to be in motion toward being a statue.

There’s one attempt at clarifying the definition that I’ve heard, which I don’t like. It states that the definition means that an object in motion is in act to the extent that it has come partway through the motion, and in potency to the extent that it is still on the way to further act. This state of being less in potency than before but not yet as much in act as it could be is motion.

But this clarification clearly just doesn’t mean the same thing as the definition. The definition states that motion is the act of a potency. In other words, the act belongs in some way to a potency. This does not come across in the clarification; the clarification describes motion as the state in between a lesser act and a greater act. “In between lesser act and greater act” and “act of a potency” are just not the same thing, no matter how you look at it.

One short thought experiment shows that the clarification is incorrect. Say someone takes two pots of water at the same temperature and puts them both on a fire. Then, he takes one off the fire while leaving the other on the fire. Now, both pots are in a state of greater heat than before while being in a state of less heat than they could be. But the one is in motion, while the other is at rest. With respect to being in between lesser and greater act, nothing differentiates the two pots of water. But with respect to being in motion, the two pots are different; one is in motion, while the other is at rest. So clearly the difference between motion and rest is not a matter of being in between lesser and greater act.

So I find this clarification misleading.

(further thoughts to follow)

(EDIT: Uncapitalized a part that was written in all-caps, because it seemed too emotional. Took out a couple of extra words.)