[MUSIC] Is motion eternal? So far in Aristotle's natural philosophy, we have been looking at the case of individual living creatures like plants and animals. We have seen Aristotle defend the claim that their nature is their form and that they are moved by their souls. Now we're going to look at Aristotle's cosmology at more global questions about change in the cosmos. Why is there motion or change at all? Did it ever start? Will it ever end? Aristotle considers these kinds of questions in the final book of The Physics, book eight. The first chapter opens by asking a very general question about change. Has motion ever come to be without having previously been? And does it perish in turn, in such a way that nothing is any longer in motion? Now in order to understand these questions and Aristotle's answers, we need to get some vocabulary straight. Motion in this passage translates the Greek term kinesis, which is a very general term for change. So we have to keep in mind that it encompasses all kinds of change not just locomotion, that is movement from place to place. So Aristotle is asking here, has there ever been a time when there was no change going on in the universe, or will there ever be such a time? Anaxagoras for example proposed that there was a time before motion began in the cosmos. And Empedocles proposes that there are times when all motion in the cosmos ceases, and then later it starts up again. Aristotle thinks both these views are mistaken, indeed, incoherent. To explain why he thinks this, he appeals to the view that for every motion there is both a mover and a thing moved. Now it's important to make sure we understand these terms properly. As Aristotle uses these terms, the moved thing, [FOREIGN], is the subject of change like the window that breaks when hit by a ball or the water that comes to a boil when heated by a fire. The mover [FOREIGN] is the efficient cause of that change the ball that breaks the window, the fire that heats the water. Now in English, we talk about moving both in the case of the subject of change and in the case of the cause. As I walk around the room we can say that I am moving around the room. In that case, I'm the subject of change. But I can also move furniture around the room, in which case my moving is the causing of change. So if you say in English, I'm moving, that's ambiguous between saying that I am in motion, as in taking a walk or that I am causing motion as when I move a chess piece on the board. But the verb Aristotle uses and that we translate as move, has only the second sense, it means cause motion, that is it's a transitive verb. So when Aristotle is talking about movers, he's always talking about the causes of change, not the subjects of change. And when he's talking about what is moved, he's talking about the subject of change, the window or the water in our examples. So to put all this vocabulary together, motion kinesis is change. The cause of change is the mover and the subject of change is the moved. Now it's worth applying these concepts to some examples. When acid turns the litmus paper pink, the motion is the turning pink. The moved, the thing that turns pink is the litmus paper and the mover, the cause of that change, is the acid. Okay, one more example, this one from Aristotle. The teacher teaches the student. Here, the motion or change, is learning. The moved, the subject of change, is the student. She's the one who learns, and the mover is the teacher. Okay, now after all this set up, we're in a position to understand the main argument Aristotle gives, in chapter one of book eight of The Physics, against the proposal that there ever was a beginning to change in the cosmos. Remember, the issue isn't whether particular motion are changes begin and end. Clearly they do. The question is, whether there was ever a time without any change, or will there ever be any such time in the future. The basic idea behind Aristotle's argument against the beginning for change is this, for every change there is a mover and a moved. That is, a subject of that change and the cause of that change. So far so good, but the mere existence of the mover and the moved don't suffice for a change. If the acid is sealed away in a flask and the litmus paper is in a box on the shelf, the litmus paper won't turn pink. If the student stays home from school, then she won't learn from the teacher. For change to happen, the mover and the moved have to be in the right conditions. In many cases, that means they have to be in proximity with each other. The acid and the litmus paper have to be in contact and both the teacher and the student have to be in school. So here's Aristotle's argument. Suppose for the sake of argument that there is a first change in the universe, and before that, there was no change. So in the time before that first change started, the mover and moved of that first change couldn't have been together in the right conditions. Otherwise, the first change would have been happening then, rather than later. So in this time before the first change, either the mover and moved didn't exist, or they existed, but they were not in the right conditions for the change. But now we have to ask, how did that first change get started? One of two things had to have happened. Either the mover and moved came into existence, now that's a change, or they moved into proximity, or into the right conditions, that's a change. So then the first change, which we hypothesized for the sake of argument can't be the first change after all. Let's apply this to an example. Suppose the first change in the universe is the litmus paper turning pink in the acid. If that's the first change and then the time before it happened the litmus paper was not in the acid. So then, in order for the litmus paper to turn pink it first has to be moved into the acid. But then that change, the relocation of the litmus paper, not it's turning pink is the first change. But if we consider how this change, the relocation of the litmus paper could have started, we get a similar problem. If it wasn't already moving toward the acid which is itself a change, something had to have changed first in order for that relocation to start. So the moral is, no matter what you posit as the first change you are going to have to posit a change that occurred prior to that. Here's how we can summarize the argument. Step one. Suppose at Time 1 there is no change in the cosmos and at Time 2 the first change in the cosmos occurs. 2. So, at Time 2, the MOVER and MOVED exist and are in the right conditions for the first change in the cosmos but at Time 1, this is not the case. Step 3. So, something must have changed between Time 1 and Time 2. So there was a change before the first change in the cosmos. That's Step 4. This style of argument is called a reductio ad absurdum, sometimes called a reductio for short. You disprove a hypothesis by showing that something absurd follows from it. In this case, Aristotle shows that if you assume that there was a first change in the universe, that's step one of the argument. Then it follows that there was a change before the first change which is incoherent. What do you think of this argument? How would you apply it to the hypothesis that the Big Bang is the first change in the universe?
