Commentary Aristotle Physics
Lecture 13
It is shown from the void itself that there is no separated void
But, even if we consider it on its own merits, the so-called vacuum will be found to be really vacuous. For just as, if one puts a cube in water, an amount of water equal to the cube will be displaced, so too in air; but the effect is imperceptible to sense.
And indeed always, in the case of any body that can be displaced, it must, if it is not compressed, be displaced in the direction in which it is its nature to be displaced—always either down, if its locomotion is downward, as in the case of earth, or up, if it is fire, or in both directions (whatever be the nature of the inserted body).
Now, in the void, this is impossible, for it is not body; the void must have penetrated the cube to a distance equal to that which this portion of void formerly occupied in the void, just as if the water or air had not been displaced by the wooden cube, but had penetrated right through it.
But the cube also has a magnitude equal to that occupied by the void, a magnitude that, if it is also hot or cold, or heavy or light, is none the less different in essence from all its attributes, even if it is not separable from them.
I mean the body of the wooden cube, such that, even if it were separated from everything else and were neither heavy nor light, it would occupy an equal amount of void and fill the same place as the part of place or of the void equal to itself.
How, then, will the body of the cube differ from the void or place that is equal to it? And, if there can be two such things, why cannot there be any number coinciding? This, then, is one absurd and impossible implication of the theory.
It is also evident that the cube will have this same volume even if it is displaced, which is an attribute possessed by all other bodies also.
Therefore, if this differs in no respect from its place, why need we assume a place for bodies over and above the volume of each, if their volume be conceived of as impassible? It contributes nothing to the situation if there is an equal interval attached to it as well.
Further, it ought to be clear by the study of moving things what sort of thing void is. But, in fact, it is found nowhere in the world. For air is something, though it does not seem to be so—nor, for that matter, would water if fishes were made of iron, for the discrimination of the tangible is by touch. It is clear, then, from these considerations that there is no separate void.
541. Now the Philosopher, taking his arguments from the void itself without any mention of motion, shows that the void does not exist.
He shows this by three reasons.
He first says (216a26) that, even considering the void in itself, without motion, it will be seen that the void spoken of by some is truly as the name “void” implies. For void means something empty and non-existent—and the claim that it exists is vain and without reason and truth. And he shows this as follows.
If anyone places a cubic body in water (such as a body having six square surfaces), an amount of water equal to the quantity of the cube must be displaced. And what is true of water is true of air, although it is not so evident, because water is more perceptible to sense than air.
By the same reasoning applied to the case of any body that can be displaced, if the parts are not compressed or enter into each other, then it must in some part be dislodged, either according to the state of a yielding body (when it has free exit)—for example, if it is a heavy body such as earth, it will yield downward, and if it is a light body such as fire, it will yield upward, and if it is a body that is light in relation to one body and heavy in relation to another, it will yield in both directions, such as do air and water—or because the body yields on account of the condition of the newly imposed body, such as when the yielding body is prevented by the imposed body from being moved according to its demands, but is moved according to the demands of the imposed body. And in general, it can be held as true that a body must yield to an inserted one, lest two bodies be in the same place.
But this will not be true in the case of the void, namely, that it must yield to the inserted body. For the void is not a body, but whatever is moved in any manner whatsoever is a body. But, if there be empty space and a body inserted in it, then the inserted body must pass through that space that previously was empty and cohabit the same space as the void—just as if water or air were not to yield to a wooden cube, but were to pass into the cube in such a way that the air and water would penetrate that cubic body and cohabit with it.
But it is impossible for a wooden cube to exist with empty space, for the wooden cube has the same magnitude as the empty space, which is supposed to be a certain dimensional space without a sensible body. And, even though the wooden cube be hot or cold, heavy or light, nevertheless the cubic body is other in account from all the sensible qualities that are its accidents, although it be not separable from them in reality. Now, what is distinct in account from the qualities is the body of a wooden cube, that which pertains to its corporeity. Now, if this body be separated from whatever is distinct from it in account, such that it is neither heavy nor light, it follows that it will occupy a volume of empty space equal to itself. Thus, the body of the wooden cube will be in the same part equal to it, which is part of the place and of the void.
On this assumption, it does not seem possible to find a difference between the body of the cube and the dimensions of the place or void. For just as the dimensions of the place or void exist without sensible qualities, so too the dimensions of the cubic body, at least according to account, are distinct from its sensible qualities. But two magnitudes of equal quantity can differ only in position. For we cannot imagine one line as distinct from another of equal length unless we imagine one in one position and the other in another. Hence, if two magnitudes are imagined together, it does not seem that they can differ, and consequently, if two bodies of equal dimensions are together, whether accompanied by their sensible qualities or not, it follows that two bodies are one. Or, if the cubic body and the space that is the place or void remain two but are still together, there is no reason why any number of bodies cannot be there. In that case, just as the cubic body is together with the space of the place or void, a third or even a fourth body ought to be able to be inserted along with both.
This, of course, is impossible. For we cannot say that it is because of matter that some other sensible body cannot exist together with the wooden cubic body, for place does not belong to a body because of its matter, except in the sense that the matter is contained under dimensions.
Hence, the impossibility of two bodies being together is not on account of the matter or of the sensible qualities, but only on account of the dimensions, in which no diversity can be found if they are equal except a diversity based on position, as was said. Therefore, since there are dimensions in empty space just as there are in a sensible body, then, just as two sensible bodies cannot be together, so neither can a sensible body be together with empty space. So, this is one unacceptable result and impossibility that follows from the aforementioned premise: namely, that two bodies would be in the same place.
542. He then gives the second reason, at “it is also evident” (216b12), saying that it is clear that a cube that is transferred to an empty space has what all other bodies have, namely, dimensions. If, therefore, the dimensions of the cube do not differ from the dimensions of the place according to account, why is it necessary to find for a body a place distinct from its own body, if place is nothing more than impassible body, that is, a body without sensible qualities? In view of the fact that a body has its own dimensions, there seems to be no necessity for it to be surrounded by other dimensions of a space equal to its own dimensions. Consequently, if the void is presumed, or place as a certain separated space, it follows that bodies do not have to be in place.
543. He gives the third reason at “further, it ought to be” (216b17), when he says that, if there were a void, it would have to be evident in mobile things. But there is no evidence of a void anywhere in the world, because what is full of air seems to be a void but is not. For air is something, although not perceptible to sight. Now, if fish were made of iron and had the same appearance as water, our sight would not be able to distinguish them from water, but it would not follow that the water, or even the fish, were non-existent: for it is not only by sight but also by touch that we can discern what is touched. Consequently, it is evident that water is something, because touch can perceive whether it be hot or cold.
From all this, it appears that there is no separate space either within or outside the universe.