How does change work, according to Aristotle?

This account lets us do physics, Aristotle thinks.

Aristotle’s (384-322 BC) Physics is a book about philosophical inquiry into nature. There are many conceptual puzzles about nature that he considers, but one of the most important, and foundational, concerns the possibility of change.

At first, change can seem quite puzzling. Certainly, to Aristotle’s predecessors, it was a challenging phenomenon to think through.

We normally think of change as the process by which something that doesn’t exist comes into existence. For example, I change when a beard goes from not existing to existing on my face. There are, of course, other times when something that does exist stops existing. Say, I shave my beard, making it go from existing to not existing anymore.

Consider what Parmenides (flourished ca. 500 BC), one of Aristotle’s most important predecessors, said about that which exists:

“For what generation will you seek for it?
How, whence, did it grow? That it came from what is not I shall
not allow you to say or think - for it is not sayable or thinkable
that it is not. And what need would have impelled it,
later or earlier, to grow - if it began from nothing?
Thus it must either altogether be or not be” (DKB8).

Parmenides means that what exists right now did not ever come into existence. There was no process of becoming that took what didn’t exist and made it be into what exists right now. Surely, that violates what our eyes and ears tell us about the world, but he means what he says: change doesn’t happen, even though it appears to.

Why not? That’s because that which does not exist literally doesn’t exist: it does the opposite of existing. So, it clearly can’t exist as something sayable or thinkable because it doesn’t exist; so, we can’t talk or think about it (despite appearances). If something is sayable, then it exists to some extent (as something that can be said). If something is thinkable, then it exists to some extent (as something that can be thought). But that which does not exist doesn’t, after all, exist. And besides, what could have taken that which does not exist and make it “grow”? The answer is: this is just impossible; you can’t act on something that doesn’t exist.

It doesn’t exist, so it can’t be brought into existence.

Parmenides presents a conceptual argument that directly undermines the phenomenon of change. Aristotle wants to refute this position by laying out exactly is going on in change.

There are two really big ideas to mention here, and I want to focus specifically on the second one.

The first is that Aristotle thinks that Parmenides completely misdiagnosed how change involves non-existence. What comes into existence is not that which simply and literally does not exist. Instead, what comes into existence is that which merely potentially exists.

Change is the actualization of something potential.

For instance, I go from being potentially bearded to actually bearded. The beard existed beforehand but merely “in potentiality.”

Once you understand this point, the thrust behind Parmenides’ conceptual argument dissolves.

But still there is a lingering question: how exactly does change work? And that question takes us to the second point, which is what I want to emphasize.

Aristotle thinks that there are three “starting points” of change. These starting points lay the foundation for any inquiry into nature. So, they are also the starting points of physics as a scientific study of the natural world.

Here they are:

1. Privation (also known as ‘lack’).

2. Form.

3. Matter.

Privation is a quality or characteristic that doesn’t exist. We just saw that Aristotle isn’t talking about non-existence as the literal opposite of existence; so, instead, he means that privation is the existence of a quality merely in potentiality. An obvious example: beardlessness (i.e., being merely potentially bearded). This is a privation because it is the lack of the quality of being bearded.

Form is the arrangement of something’s parts such that it has the property or characteristic in question. When I am bearded, the right molecules are in the right position such that I am bearded (i.e., my beard actually exists; I have a beard; etc.). ‘Form’ can be a bit of a strange way to put the point at first but what we are really saying is that qualities, such as being bearded, are arrangements or configurations of parts.

When we change, we go from lacking a property to having that property. Example: I go from being beardless to being bearded. Of course, we can also think of the opposite happening: we go from having a property to lacking that property.

In the most natural examples, privation is that which change is from, and form is that which change is into, but of course this can be reversed. After all, I gave the example earlier of shaving a beard and thus becoming beardless.

But what about the thing that undergoes the change? In this case, that would be my face. This is the thing that is changing. What about that?

That’s where matter comes in: matter is that which undergoes the change. It is the third “starting point” of change, alongside privation and form.

Another way to think of matter is this. When I grow a beard, I still have the same face. Nobody, except for Parmenides, doubts that a change has taken place, but there is something more: that which has persisted through the change. This is the matter, which underlies the privation and form.

So, we have something that change is from, something that change is into, and something that underlies the change.

Here’s an interesting complication. While Aristotle acknowledges these three starting points at first, later he explains that there really are only two: form and matter.

Since change is never from (or into) something that truly, literally, actually doesn’t exist, all change is from one form to another, while matter persists and underlies the change.

Here’s an example. I go from being beardless to being bearded. Being bearded is a form: it is an arrangement of parts such that someone would correctly say about me that I am bearded. Beardlessness is a form in itself, too. After all, being beardless is not a state of totally, literally not existing. Instead, being beardless is a state in which some molecules are in some condition or arrangement, such that I am beardless. That means it is a form, since forms are arrangements such that things have qualities. So, when I go from being beardless to being bearded, I go from having one form to having another.

We can continue to talk about the three “starting points” of change, in Aristotle’s mind, so long as we recognize that privation is not the total, absolute lack of anything and that privation is, therefore, a form, too.

This analysis, Aristotle thinks, explains what is going on in change, and it is much less of a mystery than Parmenides made it seem to be.