Commentary Aristotle Physics
Lecture 9. Opinions about the void
The investigation of similar questions about the void must also be held to belong to the physicist—namely, whether it exists or not, and how it exists or what it is—just as about place. The views taken of it involve arguments both for and against, in much the same sort of way.
For those who hold that the void exists regard it as a sort of place or vessel that is supposed to be “full” when it holds the bulk that it is capable of containing and “void” when it is deprived of that—as if “empty” and “full” and “place” denoted the same thing, though the essences of the three are different.
We must begin the inquiry by putting down the account given by those who say that it exists, then the account of those who say that it does not exist, and, third, the current view on these questions.
Those who try to show that the void does not exist do not disprove what people really mean by it, but only their erroneous way of speaking; this is true of Anaxagoras and of those who refute the existence of the void in this way.
They merely give an ingenious demonstration that air is something by straining wine skins and showing the resistance of the air, and by cutting it off in clepsydras.
But people really mean that there is an empty interval in which there is no sensible body. They hold that everything that is is body and say that what has nothing in it at all is void (so what is full of air is void).
It is not, then, the existence of air that needs to be proved, but the non-existence of an interval, different from the bodies, either separable or actual—an interval that divides the whole body so as to break its continuity, as Democritus and Leucippus hold, and many other physicists (or even perhaps as something that is outside the whole body, which remains continuous). These people, then, have not reached even the threshold of the problem.
But rather, those who say that the void exists provide more reasons. They argue, for one thing, that change in place (namely, locomotion and increase) would not be. For it is maintained that motion would seem not to exist if there were no void, since what is full cannot contain anything more.
If it could, and there were two bodies in the same place, it would also be true that any number of bodies could be together, for it is impossible to draw a line of division beyond which the statement would become untrue.
If this were possible, it would follow also that the smallest body would contain the greatest, for “many a little makes a mickle.” Thus, if many equal bodies can be together, so also can many unequal bodies.
Melissus indeed infers from these considerations that the all is immovable, for he says that, if it were moved, there must be void, but void is not among the things that exist. This argument, then, is one way in which they show that there is a void.
They reason from the fact that some things are observed to contract and be compressed, as people say that a cask will hold the wine that formerly filled it along with the skins into which the wine has been decanted, which implies that the compressed body contracts into the voids present in it.
Again, increase is also thought to take place always by means of void, for nutriment is body, and it is impossible for two bodies to be together.
A proof of this they find also in what happens to ashes, which absorb as much water as the empty vessel.
The Pythagoreans, too, held that void exists and that it enters the heaven itself, which inhales it, as it were, from the infinite air. Further, it is the void that distinguishes the natures of things, as if it were like what separates and distinguishes the terms of a series. This holds primarily in the numbers, for the void distinguishes their nature. These, then, and so many, are the main grounds on which people have argued for and against the existence of the void.
494. Having discussed place, the Philosopher now begins to treat of the void.
Concerning it, he does two things:
first, he manifests his intention:
second, he executes it, at “those who try to show” (213a22; [496]).
As to the first, he does two things:
first, he shows that it is proper for the natural philosopher to deal with the void;
second, he shows what order should be followed in determining the void, at “we must begin” (213a19; [495]).
Therefore, he first says (213a12) that it is the task of the natural philosopher to determine about the void just as it was his task to determine about place: whether it exists and what it is. For the same reasons have led to belief or disbelief in the existence both of place and of the void. For those who posit a void think of it as a place and vessel, which vessel or place seems to be full when it has within it the mass of some body, but when it does not, it is said to be a void. It is as though place and void and full are the same in subject, any differing among them being only in the mind.
495. Then, at “we must begin” (213a19), he shows what order must be followed in determining about the void. And he says that we must begin by giving the reasons of those who claim that the void exists, then the opinions of those who claim it does not exist, and then the general opinions about the void, namely, what belongs to the account of the void.
496. Then, at “those who try to show” (213a22), he begins to follow this program:
first, he sets down preliminary notions that are necessary for discovering the truth about the void;
second, he begins to search for the truth, at “let us explain again” (214b12; [520]).
About the first, he does two things:
first, he gives the reasons of those who posit or deny the existence of the void;
second, he gives the common opinion about the void, showing what is included in its account, at “as a step towards” (213b30; [506]).
As to the first, he does two things:
first, he gives the reason of those who deny the existence of the void;
second, the reasons of those who affirm it, at “but rather” (213b3; [499]).
497. He says first, therefore (213a22), that some of the earlier philosophers desirous of demonstrating that the void does not exist erred by not arguing against the reasons given for the existence of the void. For they did not show that the void does not exist, but rather gave their reasons to show that something full of air is not a void, as is evident from Anaxagoras and others who reasoned like him. In order to destroy the void, they wanted to demonstrate that air is something, and thus, since the void is that in which nothing exists, it followed that something full of air is not a void. In debating with their adversaries, they showed that air is something by means of wine skins that, when inflated, could support a weight, which would not happen unless air were something. This also showed that air has strength.
They also showed it by taking the air in clepsydras, vessels that absorb water; in these vessels, water is drawn in by drawing in air, or water is prevented from entering unless the air be withdrawn. It is clear, therefore, that they are not objecting against those who posit a void, because all such claim it is empty space in which no sensible body exists, for they assume that whatever exists is body perceptible to sense; thus, where no sensible body exists, they believe nothing exists. Hence, since air is a body scarcely perceptible to sense, they thought that where there was nothing but air the void existed.
498. Therefore, to destroy their position, it is not enough to show that air is something, but also one must show that there is no space without a sensible body.
Space was supposed to be a void in two ways:
first, as something separated from bodies, as though we were to say that the space within the confines of a house is a void;
second, as something existing in act between bodies, preventing them from being continuous, as Democritus and Leucippus and many of the other natural philosophers held.
They imagined that, if the totality of being were continuous, all things would be one, for there would be no more reason for distinguishing bodies at one point rather than another. Hence, between all distinct bodies, they posited intervals of empty space in which no being existed. And, since Democritus posited that bodies are composed of many indivisible bodies, he posited between those indivisibles certain empty places that he called “pores.” In this way, he explained that all bodies are composed of the full and of the empty. Or, if the entire body of the world were continuous and no such empty place existed between the parts of the universe, they yet posited a void existing outside the universe. It is evident, therefore, that the aforementioned philosophers who tried to reject the void did not answer the problem as laid down by others. For they should have shown that the void does not exist in any of those ways.
499. Then, at “but rather” (213b3), he sets forth the reasons of those who posited a void:
first, of those who spoke of the void naturally;
second, of those who spoke of it not as natural philosophers, at “the Pythagoreans, too” (213b22; [505]).
As to the first, he does two things:
first, he mentions the reason given by those who held that the void is a space separated from bodies;
second, by those who posited a void in bodies, at “they reason from the fact” (213b15; [502]).
Concerning the first he does two things:
first, he gives the reason of those who posited a void;
second, he says how Melissus used that reason conversely, at “Melissus indeed” (213b12; [501]).
500. He first says (213b3) that those who affirmed the existence of the void gave more apposite reasons.
One such reason was that motion in respect of place—that is, change of place and increase—as was said above, would not exist if there were no void. They showed this in the following manner. If something is in motion according to place, it cannot be moved into what is full, because a place filled with one body cannot receive another. For if it received it, there would then be two bodies in the same place, and the same would follow for any body, for there is no reason why many bodies could not be in the same place if two could. And if that were to happen—namely, that any number of bodies were in the same place—it would follow that the smallest place could receive the largest body, since many small things form one large thing.
Hence, if any small equal bodies could exist in the same place, so too could many. And so, having proved this conditional position—that if there is motion, there is a void—they argue there is a void by positing the antecedent: there is motion; therefore, there is a void.
501. Then, at “Melissus indeed” (213b12), he shows how Melissus, supposing the same conditional, argued in a contrary manner from the denial of the consequent thus: if motion exists, there is a void; but there is no void; therefore, motion does not exist. Consequently, the totality of being is immobile.
Thus, the foregoing is one way in which some proved that the void exists after the fashion of something separate.
502. Then, at “they reason from the fact” (213b15), he lists three reasons given by those who held that the void exists in bodies.
The first of these is based on things that condense. For in the case of things that can be compressed, it seems that the parts come together and fit in together and press down and compress each other such that, as is held, casks will hold as much wine with the wine skins as without, especially if the wine skins are thin, for in the wine skins, the wine seems to become condensed. This condensation they believed to take place as though in the condensed body the parts entered into certain empty spaces.
503. The second reason, at “again, increase is also thought” (213b18), is based on increase: a body grows on account of food, which is a body; but two bodies cannot exist in the same place; therefore, there must be, in the body that has grown, certain voids in which the food may be received. Consequently, there must be a void in order that food be taken in.
504. The third reason, at “a proof of this” (213b21), is based on a vessel full of ashes being able to absorb as much water as the empty vessel. This would not be the case unless there were empty spaces between the parts of the ashes.
505. Then, at “the Pythagoreans, too” (213b22), he gives the opinions of the non-natural philosophers about the void. And he says that the Pythagoreans also posited a void that entered into the parts of the universe from the heavens, on account of the infinite void that they supposed existed outside the heavens—a void like some infinite air or infinite breath:
just as a person who breathes divides by means of his breath certain things that are easy to divide, such as water or similar things, so it was that the things of this world became distinct by some being as though through breathing. They did not understand this to happen except through a void, as was mentioned in regard to Democritus—as though the void were nothing other than the distinction between things.
And, because the first distinction and plurality is found in numbers, they first of all posited a void in numbers, such that it is through the nature of the void that one unit would be distinct from another—such that number would not be continuous, but would have a discrete nature. But, because they spoke of the void in a quasi-equivocal manner, calling the distinction of things “a void,” Aristotle does not discuss this opinion below.
Finally, in summary, he concludes that we have given the reasons that some posit a void and some do not.