Last week I talked about the four causes: the four things you can find in any change. The last of the four is the final cause, which you can think of as the reason for the change; and I said I’d talk about that next. But I’ve changed my mind; I want to say a little more about change, first, and how Aristotle looks at it.

Every change has a beginning, a middle, and an end. First, consider a rock perched on a cliff. There’s a slight earthquake (the efficient cause) and the rock is shaken lose. It falls to the ground below, bounces, and comes to rest. We begin with the rock in one place; it moves; we end with the rock in another place. The rock itself is unchanged; but it has lost one form, its initial position, and gained a different form, its new position. Next, consider a green apple that in the course of time turns red. It was green; it changes color; it is now red.

There are a couple of things to note, here.

First, in every such change of this kind the thing loses a form and gains a form, and they have to be two distinct forms. (If they were the same form, no change would have occurred.) These forms are frequently referred to as contraries, because they can’t both be true at the same time. The rock might be here, and it might be there, but it can’t be in both places at once. The apple might be mostly green, or it might be mostly red, but it can’t be mostly green and mostly red at the same time.

Second, Aristotle isn’t concerned with time, with how fast the change occurs. It took me a long time to really wrap my head around this. When we think about physics, time is everything. If drop a ball, how long it will take to hit the floor given the acceleration of gravity? We take a change, and we divide the time it takes into the tiniest possible increments, and we look at just exactly how everything moves during each increment, and we devise a mathematical model (such as Newton’s Laws of motion) that describes the movement that we see.

Aristotle wasn’t doing that. He wasn’t trying to understand the exact progress of a particular change over time, but rather he was asking how change is possible at all? What does it mean to say that the apple turned red? What is involved?