Commentary Aristotle Physics

Aquinas, Thomas

Section 61 of 169

Underlined text was edited by AI to fix errors.

Lecture 8 Solution of difficulties about place It is clear, too, from these considerations that all the problems that were raised about place will be solved when it is explained in this way: there is no necessity that the place should grow with the body in it; nor that a point should have a place; nor that two bodies should be in the same place; nor that place should be a corporeal interval, for what is between the boundaries of the place is any body that may chance to be there, not an interval in body. And place is also somewhere not in the sense of being in a place, but as the limit is in the limited, for not everything that is is in place, but only movable body. Also, it is reasonable that each kind of body should be carried to its own place. For a body that is next in the series and in contact (not by compulsion) is akin, and bodies that are united do not affect each other, while those that are in contact interact on each other. Nor is it without reason that each should remain naturally in its proper place. For this part has the same relation to its place as a separable part to its whole, as when one moves a part of water or air. So, too, air is related to water, for the one is like matter, the other form—water is the matter of air, and air is, as it were, the act of water, for water is potentially air, while air is potentially water, though in another way. These distinctions will be drawn more carefully later. On the present occasion, it was necessary to refer to them, but what has now been stated obscurely will then be made more clear. If the matter and the act are the same thing (for water is both, the one potentially and the other completely), water will be related to air in a way as part to whole. That is why these have contact: it is coupling when both become actually one. This concludes my account of place—both of its existence and of its nature. 487. After explaining what place is, the Philosopher now uses his definition to resolve the doubts that were raised about place. Now there were mentioned above six reasons to show that place does not exist. Of these, he bypasses two: the one in which it was asked whether place be an element or a composite of elements; the other in which it was shown that place cannot be reduced to any genus of cause. He bypasses them because no one who posited place took it either as an element or as a cause of things.

Hence he makes mention only of the four remaining.

488. One of these was that, since place never lacks a body, and a body never lacks a place, it seemed to follow that, if the body grew, the place would grow. Now, this would follow if it were supposed that place were a space coextensive with the dimensions of the body, so that, as the body increased, so would the space. But this does not follow from the given definition of place, namely, that it is the boundary of the container.

489. Another argument was that, if the place of a body be distinct from the body, then the place of a point would be distinct from the point; therefore, it did not seem possible for place to be distinct from the body, since the place of a point is not distinct from the point.

But this argument was based on the imagining of those who opined that place is the space coextensive with the volume of the body, such that a dimension of space would correspond to a dimension of the body, and in like manner to each point of the body. This, however, need not be said if we suppose that place is the boundary of the container.

490. Another argument was that, if place is anything, it must be a body, since it has three dimensions. Consequently, there would be two bodies in the same place. But according to those who agree that place is the boundary of the containing body, it is not necessary to say that two bodies would be in the same place, or that there is some bodily space intervening between the boundaries of the containing body, but that there is some body there.

491. Likewise another argument was that, if everything that exists is in place, it will follow that even a place is in place. This argument is easy to answer if we suppose that place is the boundary of the container, for according to this, it is clear that place is in something—namely, in the containing body—but it is there not as in a place, but as a boundary in a finite thing, just as a point is in a line and a surface in a body. For it is not required that everything that is be in something as in a place; this is required only of a mobile body, for it is motion that led to distinguishing between the thing in place and the place itself.

492. Then, at “also, it is reasonable” (212b29), he uses his definition to give a reason for the properties of place.

First, as to the fact that a body is naturally borne to its proper place;

second, as to the fact that a body naturally rests in its own place, at “nor is it without reason” (212b33; [493]).

He says first that, if place be taken to be the boundary of the container, the reason that each body is naturally borne to its own place can be given. It is because the containing body (which is next to the contained and located body, and which is touched by it so that the boundaries of both are together not by force) is akin to it in nature. For the order of position in the parts of the universe follows upon the order of nature. For the heavenly body, which is supreme, is the most noble; after it, among the other bodies, the noblest in nature is fire, and so on down to earth. Hence, it is clear that the lower body that is situated according to position, next to the higher body, is akin to it in the order of nature.

And therefore he adds, not by compulsion, in order to point out the natural order of position to which the order of nature corresponds and to exclude a forced order of position, as when a body of earth is above air or water by force. Two such bodies that are next to one another in the natural order of position and are disposed to be together in the natural order of natures do not affect each other; that is to say, when they are made continuous to each other and become one—and for this they have an aptitude on account of the similarity of their natures—then they do not interact.

But when distinct things are in contact, they mutually interact on account of the contrariety of their active and passive qualities. Therefore, it is the kinship of nature existing between the container and the thing contained that explains why a body is naturally moved to its own place: for the rank in natural places must correspond to the rank in natures, as was said. But such a reason cannot be assigned if place is taken to be space, for in the separated dimensions of space, no order of nature can be considered.

493. Then, at “nor is it without reason” (212b33), he gives the reason that bodies naturally rest in their own place. And he says that this happens reasonably if we grant that place is the boundary of the containing body, for according to this, the contained body is related to the containing body after the manner of a part to a whole—a separated part, however. This is abundantly clear in bodies that are easy to divide, such as air or water, for their parts can be moved by something in the whole just as a thing in place is moved in a place. And this also is true not only according to the figure of containing one under the other, but even according to the properties of their nature. For air is related to water as the whole, because water is like matter and air like the form: water is as the matter of air, and air is as the form of water. This is so because water is in potency to air absolutely.

Now, while it is true that air is in potency to water in some other ways, as will be explained later in De generatione, it is necessary for the present to accept this in order that we may explain our proposition. Here it is not declared as a certainty, but in the De generatione it will be proved with greater certainty. For it will be said there that, when air is generated from water, it is corruption in a certain respect and generation simply, because a more perfect form is being introduced and a less perfect one is being removed. But, when water is generated from air, it is corruption simply and generation in a certain respect, because a more perfect form is being removed and an imperfect one being introduced. Consequently, water is in potency to air absolutely as the imperfect to the perfect, but air is in potency to water as the perfect to the imperfect. Hence, air is as the form, and as the whole that is like the form; water, however, is as the matter and as a part, which pertains to the account of matter.

Therefore, although the same thing is both matter and act, because the water contains both in itself, still properly speaking, the latter, (namely, the water) is in potency as an imperfect thing, but the former (namely, the air), in act as a perfect. Hence, water will be related to air somewhat as part to whole. And therefore these things, the air and the water, when they are distinct, are in contact, but when they form a unity by one passing into the nature of the other, then coupling occurs, that is, continuity. Therefore, just as the part naturally is at rest in the whole, so also a body naturally rests in its natural place.

Note, however, that the Philosopher is speaking here of bodies according to the substantial forms that they have under the influence of the heavenly body, which is the first place, and which gives to all other bodies the power to act as places. But, if we consider active and passive qualities, there is contrariety among the elements and one tends to destroy another.

Finally, he concludes in summary that it has been stated that place exists and what place is.