LECTURE 11 (214 b 12-215 a 23)

IT IS SHOWN FROM MOTION THAT THERE IS NO SEPARATED VOID

             520. Having given the opinions of others concerning the void, and having stated the meaning of the word 'void', he begins here to seek out the truth.

             First he shows that there is no separated void. Secondly, where he says, 'There are some who think . . .' (216 b 22), he shows that a void is not present in bodies.

             Concerning the first part he makes two points. First he shows from motion that there is no separated void. Secondly, where he says, 'But even if we consider . . .' (216 a 27), he shows the same thing by considering the void itself.

             Concerning the first part he makes two points. First he shows from motion that there is no separated void. Secondly, where he says, 'Further, the truth . . .' (215 a 24), he shows the same thing by means of the speed and slowness in motion.

             521. Concerning the first part he gives six arguments. In the first argument he says that it is necessary to say again that there is no separated void, as some hold. He says 'again' because this has already been shown in the treatment of place. For if place is not space, it follows that there is no void, as was said.

             But now he proves the same thing again from motion. For they posit a void because of motion, as was said. However it is not necessary to posit a void because of motion. The void seems especially to be the cause of local motion. But it is not necessary to posit a void because of local motion, since all simple bodies have natural local motions. Thus the natural motion of fire is upwards, and the motion of earth is downwards and toward the middle. Hence it is clear that the nature of each body, and not a void, is the cause of local motion. Indeed there would be a void if natural bodies were moved because of the necessity of the void. Moreover if there is no cause of local motion, there cannot be a cause of any other motion or of any other thing. Therefore the void would be useless.

             522. He gives the second argument where he says, 'Again, if void . . .' (214 b 18). The argument is as follows.

             If there is a void, the cause of natural motion and of natural rest cannot be established. For it is clear that a body is naturally moved to its own natural place and is naturally at rest in it because of the agreeableness which the body has with that place and because it does not agree with the place it left. But a void does not have any nature through which it can agree or disagree with a natural body. If, therefore, there is a void, as a certain place deprived of body, one will not be able to designate the part to which that body is naturally moved. For it cannot be said that it is moved to any part. But this we see is false to the senses, because a body naturally leaves one part and naturally arrives at another.

             And this same argument avails against those who hold that place is a certain separated space in which a mobile body is moved. For this will not explain how a body has position in such a place, or how it is moved or is at rest. For the dimensions of space have no nature by which a similitude or dissimilitude to a natural body can be established. And the argument concerning the void has the same merit as the argument concerning 'upwards and downwards', that is, concerning place, whose parts are upwards and downwards. For those who posit a void say that it is place.

             Those who posit a void and those who hold that place is space not only cannot explain how something is moved and is at rest in respect to place, but they also cannot explain how something is in place or in a void. For if place is held to be space, it is necessary that the whole body be placed in that space. But according to those who hold that place is the terminus of the containing body, this is not the way in which that which is located is in place as in something separated and as in a containing and sustaining body. It seems to be of the nature [ratio] of place that something is in place as in that which is separated and existing outside. For if a part of a body is not outside of that body, it will not be in it as in a place but as in a whole. Therefore the nature [ratio] of place and of that which is located is such that place is outside of that which is located. But this is not the case if place is a space into which a whole body is immersed. Therefore space is not place. And if space is not place, it is clear that there is no void.

             523. He gives the third argument where he says, 'If people say that . . .' (214 b 28).

             He says that although the ancient philosophers held that there must be a void if there is motion, the contrary is true. For if there is a void, there is no motion.

             He proves this by a comparison. Some have said that the earth is at rest at the centre because of the similitude of parts surrounding it on all sides. Thus the earth is at rest because there is no reason why it should be moved toward one part of its surroundings rather than another. And for the same reason it is necessary that that which is in a void is at rest. For it cannot be explained why it should move to one part rather than another. A void, as such, has no differences in its parts, for of nonbeing there are no differences.

             524. He gives the fourth argument where he says, 'The second reason is this . . .' (215 a 1).

             Natural motion is prior to violent motion, since violent motion is only a certain deviation from natural motion. Therefore, when natural motion is removed, all motion is removed. For when the prior is removed, the posterior is removed. But when a void is posited, natural motion is removed, for the difference of the parts of place to which natural motion is directed is removed. This also happens when an infinite is posited, as was said above.

             But there is this difference between the void and the infinite. If there is an infinite, in no way can there be an up or down or middle, as was said in Book III. However, if there is a void, these things can be, but they do not differ from each other. For there is no differentia of nothing and of non-being, and consequently of a void, since a privation is also non-being. But natural change of place requires a difference of places, for diverse bodies are moved to diverse places. Hence it is necessary that natural places differ from each other. Therefore, if there is a void, there will be no natural change of place. And if there is no natural change of place, there will be no change of place. Hence if there is any change of place, there cannot be a void.

             525. He gives the fifth argument where he says, 'Further, in point of fact . . .' (215 a 13).

             Concerning this argument it must be considered that there is a certain difficulty about things which are thrown. For it is necessary that the mover and the moved be together, as is proven below in Book VII. Nevertheless, that which is thrown is found to be moved even after it is separated from the thrower, as appears in a stone that is thrown and an arrow that is shot by a bow. Therefore, on the supposition that there is no void, this question is solved by means of the air in which the medium is refilled.

             This is explained in two ways. Some say that things which are thrown are moved even after they are no longer being touched by the thrower because of 'antiparistasim', that is, because of a rebounding or a co-resistance. For the moved air is rebounded to another air, and that to another, and so forth. And by such a rebounding of air to air, the stone is moved.

             Others say that the air, which exists as a continuum and is set in motion by the thrower, strikes the thrown body more quickly than the motion by which the thrown body is naturally carried to its proper place. Hence because of the speed of the motion of the air, the thrown body, for example, a stone or something of this kind, is not allowed to fall downward, but is carried on by the impulse of the air. But neither of these causes could be posited if there were a void. Thus a thrown body would be moved only while held, as for example, by the hand of the thrower, and it would immediately fall when it leaves the hand. This is contrary to what we see. Therefore there is no void.

             526. He gives the sixth argument where he says, 'Further, no one could say . . .' (215 a 19). The argument is as follows.

             If there is motion in a void, no one can explain why that which is moved stops somewhere. For there is no reason why it should be at rest in one part of the void rather than in another: neither in things which are moved naturally, since there is no difference in the parts of a void, as was said above, nor in things which are moved by violence. For we say that violent motion ceases when the rebounding or impulse of air--according to the two assigned causes -ceases. Therefore it will be necessary either that every body is at rest and nothing moves, or if something is moved, that it be moved ad infinitum, unless some larger body, which impedes its violent motion, gets in its way.

             Moreover, to confirm this argument, he adds the reason why some hold that motion occurs in a void, that is, a void gives way and does not resist a mobile body. Hence, since a void gives way equally on all parts, the body is carried ad infinitum in any part.