[MUSIC] Nature and substance. Does Aristotle's analysis of change in the Physics, require him to revise the conclusions he defended in the categories about which entities are the primary substances? Some people do draw this conclusion, Aristotle tells us in chapter one of book two of the Physics. Some people, he says, think that the nature and substance of a natural thing is the primary constituent present in it. So that the nature of a bed, for instance, would be wood, and the nature of a statue would be the bronze. And if each of these things is related to something else in the same way, bronze and gold, for instance, to water, bones and wood to earth, and so on with anything else, that thing is their nature and substance. This is why some people say that fire or earth or air or water is the nature of the things that exist. Whichever one or more of these a person selects, he says that this, or these, are all the substances there is, and he takes everything else to be attributes, states, and conditions of these things. Those who take this position are drawing the surprising conclusion that we noted last lecture when reflecting on the analysis of change that Aristotle puts forth in book one of the Physics. If Socrates and Fido come to be from their underlying matter, earth, air, fire, and water, doesn't this make earth, air, fire, and water the primary substances? And Socrates and Fido merely attributes, states, and conditions of these more fundamental entities? Must we demote Socrates and Fido from the status of substance in our ontology and classify them with inherent entities instead. Aristotle doesn't think so. Towards the end of book one, after introducing the analysis of change that seems to encourage some people to draw this conclusion, he allows that matter is close to being a substance and in a way is a substance. But in book two, he continues to insist that individual humans, animals, and plants are substances, not just arrangements or properties of earth, air, fire, and water. To defend this conclusion, however, he needs something better than the subject criterion for being a substance. In book two, he develops a new criterion for being a substance. Natural things are substances. We can see this new criterion reflected in the way he articulates the dispute with his opponents. They claim that the nature and substance of a natural thing is its primary constituents. In their view, earth, air, fire, and water are the nature and substance of things. But what does nature have to do with being a substance? Well we've spent some time examining what Aristotle means by substance. Now we need to see how he defines nature. What is nature? Or, as Aristotle tends to put it, what is a nature? Aristotle opens book two of the Physics by drawing a distinction between things that are natural, like animals, plants, and elemental earth, air, fire, and water, and things that are not. The distinguishing feature of a natural thing, he explains, is that it has within itself a principle of motion and stability in place, in growth and decay, or in alteration. Now it's relatively easy to see what he has in mind by claiming that animals and plants have an internal principle of change. Plants and animals grow from the inside as it were. In contrast to a bed or a table, whose parts are assembled by the carpenter, who is external to the bed or table. The bed and table aren't assembling themselves the way the growing oak tree is. Animals have, in addition, the further ability to move themselves about from place to place, the power of locomotion. A deer running across the field is, we might say, self propelled, whereas the ball that is tossed across the field is moved by an external principle, the thrower. Balls don't pick themselves up and go somewhere, but animals do. So much for the natural motions of plants and animals. What about the elemental bodies, which also appear on Aristotle's list of natural entities? What sorts of movements does he attribute to them? Heraclitus, we saw, is impressed by the flickering motion of fire. But that's not what Aristotle has in mind. In his view, all the elements have a natural place in the cosmos, earth at the center, fire at the periphery, with air just below fire, and water just below air. When an elemental body is not in its natural place, it moves toward that place, unless something gets in the way. So here on the ground, the natural motion of elemental earth and water is to go down, while that of fire and air is to go up. We have seen what a nature is for Aristotle, so now the question is, what has a nature? The natural motions of elemental earth, air, fire, and water can sometimes be observed in macroscopic bodies. For example, a chair is made of wood, and wood's primary constituent, according to Aristotle, is earth. So the chair will go down if you push it off the balcony or if the floor gives way beneath it. In another example, a helium filled balloon will go up if you don't hold it down. So you might wonder whether the chair's falling or the balloon's rising will also count as natural motions for Aristotle, since there isn't an external principle that is moving them. It's the internal air or earth that is doing the work. Now, Aristotle says no. And his reason for saying no will help us understand the last part of his definition of nature. The chair is not a natural thing, Aristotle says, even though its natural tendency is to travel downward. But why not? If a natural tendency to travel downward is enough to make Earth natural, why isn't it enough in the case of the chair? Aristotle's answer is that the chair has a principle of downward motion only insofar as it is made of earth, not insofar as it is a chair. This is what he means when he says that the internal principle of change in a natural thing has to belong to it not coincidentally, but rather in its own right. So the chair does have an internal principle of downward motion. But not insofar as it is a chair, only insofar as it is earth. Elemental earth, by contrast, has this principle of downward motion in its own right, insofar as it is earth. So earth, rather than the chair, is a natural thing. Now once Aristotle has clarified what he means by nature, and a natural thing, he says, a nature then, is what we have said, that is, an internal principal of change that belongs to its subject, non-coincidentally. And that things that have a nature are those that have this sort of principle. All these things are substances. So naturally things are substances. That means, if Aristotle can defend the claims that Socrates and Fido are natural things, then he can establish that they are substances after all. But can he defend his view that they are natural? Certainly, animals and plants are on the list of natural things that opens chapter one of book two. Aristotle thinks they are natural, but his opponents are those who think that fire or earth or air or water is the nature of the things that exist. That is, they think that earth, air, fire, and water are the internal principles of all natural changes. So when the oak sapling grows into a mature tree, an internally produced set of changes, this is simply the earth, air, fire, and water doing their natural things. Moving in their natural directions, albeit in a very complicated arrangement. The internal principal of growth that is undeniably within the oak tree still does not belong to the oak tree insofar that it is an oak tree. That is, in its own right. But rather, it belongs only insofar that it is made of earth, air, fire, and water. On the opponent's view, the sapling growing into a mature oak is like the chair falling to the ground. The principle of motion that drives the growth belongs to earth, air, fire, and water in their own right, but to the tree, only coincidentally. Thus the oak tree is not a natural thing in their view anymore than the chair is. This is the position of those who say that matter is nature. That whatever internal principal of change a tree or an animal might have belongs to its material constituents. Not to what it is as a tree or animal. Aristotle, on the other hand, thinks that plants and animals have internal principles of change that belong to them insofar as they are what they are. That is, in virtue of their form. Thus Aristotle defends the claim that at least in the case of organisms, such as plants and animals, it is their form, more than their matter, that is their nature. Another way of translating this phrase, which captures Aristotle's point even better I think, is that form rather than matter is nature.