LECTURE 14 (216 b 21-217 b 28)

THERE IS NO VOID IN BODIES

             544. After the philosopher has shown that there is no separated void, he here shows that there is no void in bodies.

             Concerning this he makes three points. First he gives the argument of

those who posit such a void. Secondly, where he says, 'Now, if they mean . . .' (216 b 30), he disproves their position. Thirdly, where he says, 'Since we deny . . .' (217 a 10), he answers their argument.

             545. He says, therefore, first that there were some philosophers who, by arguing from rarity and density, thought that there is a void in bodies. For it seemed to them that rarefaction and condensation occur because of a void intrinsic to bodies. They said that, if there were no such rarity and density, then it was not possible for the parts of a body to come together with each other and for a body to be compressed by condensation. And if this were not so, then inconsistencies resulted both in regard to local motion and in regard to generation and corruption, or alteration.

             This would be true in regard to local motion because it will be necessary to say either that there is no motion at all or that the whole universe is moved by one motion, as the philosopher Xuthus said. This is so because, if a body is moved locally, then, when it takes a place occupied by another body, that body must be expelled and tend to another place, and again the body that is there must go to another place. And unless a condensation of bodies occurs, it will be necessary that all bodies are moved.

             In regard to generation or alteration this inconsistency follows. There will always occur an equal change of water to air and of air to water. For example, if air is generated from one measure of water, then it is necessary that somewhere else water be generated equal to the amount of air that was generated. But the quantity of air is greater than the quantity of water from which it is generated. Therefore, the generated air occupies a larger place than the water from which it was generated. Thus it would be necessary either that the whole body of the universe occupies a larger place or that somewhere an equal amount of air is converted into water. Or else one must say that there is a void within bodies so that a condensation of bodies occurs. For they did not think that bodies could be condensed or rarefied unless a void existed in them.

             546. Next where he says, 'Now, if they mean . . .' (216 b 30), he refutes the above position. He does this first according to one understanding of it, and secondly according to another, where he says, 'But if they mean . . .' (216 b 33).

             He says, therefore, first that those who say that there is a void in bodies can understand this in two ways. The first interpretation is that in each body there are many void holes, as it were, which are separated in site from the other filled parts, as is seen in a sponge, or in a pumice stone, or in other such things. The second interpretation is that the void is not separated in site from the other parts of the body, as if we would say that the dimensions which they call a void enter into all the parts of the body.

             But if they say that a void is in bodies in the first way, then this is clearly disproved from what was said above. For in that argument it was shown that there is no void separated from bodies nor is there any place which has its own space beyond the dimensions of bodies. With the same argument it can be proven there is no rarefied body which has within itself some void spaces distinct from the other parts of the body.

             547. Next where he says, 'But if they mean . . .' (216 b 33), he disproves with four arguments the above mentioned position taken according to the second interpretation.

             Therefore he says that, if a void is not in bodies as something separable and distinct from the other parts, but nevertheless a void is present in bodies, then this is less impossible. For the inconsistencies given above against a separated void do not follow. Nevertheless certain other inconsistencies do follow.

             First, the void will not be the cause of all local motion, as they intended, but only of upward motion. For a void, according to them, is the cause of rarity. But a rare thing is found to be light, as is clear in fire. And a light thing moves upwards. Hence the void will be the cause only of upward motion.

             548. He gives the second argument where he says, '. . . second, the void turns out . . .' (217 a 2).

             He says that, according to those who posit a void in bodies, the void is the cause of motion, but not as that in which a thing is moved (which is the way in which the void is the cause of motion for those who say that a void is a separated space). Rather they hold that the void is the cause of motion insofar as the intrinsic void itself moves bodies; as if we would say that inflated bags, which are carried upwards because of their lightness, also carry upwards whatever they contain. Thus the void present in bodies carries along with itself the body in which it is.

             But this seems to be impossible. For it would then be necessary for the void to be moved and for the void to have some place. And since the void and place would be the same, it would follow that the interior void has an exterior void in which it is moved. This is impossible.

             549. He gives the third argument where he says, 'Again, how will they . . .' (217 a 5).

             He says that, if the void is the cause of upward motion by carrying a body upwards, then, since there is nothing to explain downward motion, there will be no reason why heavy bodies are moved downwards.

             550. He gives the fourth argument where he says, 'And it is plain . . .' (217 a 6).

             He says that, if rarity causes upward motion because of its voidness, then it will be necessary for a thing to be moved upwards more quickly in proportion to its being more rare and more void. And if a thing were completely void, it would be moved with the greatest speed.

             But this is impossible. That which is completely void cannot be moved for the same reason by which it was shown above that there cannot be motion in a void space. For there would be no comparison of the speeds of the void and of the plenum in any determinate proportion, either in respect to the space or in respect to the mobile body, because there is no proportion of a plenum to a void. Therefore, the void cannot be the cause of upward motion.

             551. Next where he says, 'Since we deny that . . .' (217 a 10), he answers the argument given above.

             First he repeats it, explaining it more, and secondly he answers it, where he says, '. . . our statement is based . . .' (217 a 21).

             He says, therefore, first that, since we say that there is no void, either in bodies or outside them, it is necessary to answer the arguments which others bring up, because they present real difficulties.

             First he discusses local motion. There will be no local motion at all unless there be rarity and density, which they thought could not be without a void. Or else it will be necessary to say that, when any body is moved, the whole heaven is moved upwards, or a part of it, which they called 'the disturbance of the heavens'. Moreover in regard to generation and corruption, it will be necessary that water comes to be from air, and elsewhere air comes to be from water, in equal amount. For, since more air is generated than water, then it is necessary (unless there is condensation, which they believed could not occur without a void) either that the body which is held to be ultimate in common opinion (that is, the celestial body) is expanded by the excess of inferior bodies, or else in some place an equal amount of air is converted into water, so that the whole body of the universe is always found to be equal.

             Now since it would be possible to object in some way against what Aristotle has said about local motion, he repeats the above argument again in order to refute it. And he says, '. . . or that nothing moves' (217 a 18). For according to the above argument a disturbance of the heavens occurs whenever anything is moved. This is true unless the motion is understood to be circular; for example, A is moved to place B, and B to place C, and C to place D, and D to place A. In the case of circular motion it will not be necessary that the whole universe is disturbed by one motion. But we see that not all of the local motions of natural bodies are circular, for many things are moved in a straight line. Hence a disturbance of the heavens would follow unless there is condensation and a void.

             This, therefore, is the reason why some hold that a void exists.

             552. Next where he says, '. . . our statement is based . . .' (217 a 21), he solves the argument given above. The whole force of the given argument consists in the position that rarefaction and condensation occur by means of a void. Hence Aristotle answers the argument by showing that rarefaction and condensation occur without a void.

             First he explains his position, and secondly, where he says, 'From what has been said . . .' (217 b 20), he induces the conclusion which he primarily intends.

             Concerning the first part he makes three points. First he explains his position with an argument, secondly by an example, where he says, 'For as the same matter . . .' (217 a 34), and thirdly by the effects of rarity and density, where he says, 'The dense is heavy . . .' (217 b 12).

             Concerning the first part he makes two points. First he sets forth certain things which are necessary for his position, and secondly he proves his position, where he says, 'The same matter also serves . . .' (217 a 27).

             553. He sets forth four things which he takes 'from the subjects', that is, from things which are supposed in natural science, and which were explained above in Book I.

             The first point is that there is one matter for contraries, such as hot and cold, or any other natural contraries. For the nature of contraries is such that they occur in the same thing.

             The second point is that everything which is in act necessarily comes to be from that which is in potency.

             The third point is that matter is not separable from contraries so that it exists apart from them. But, nevertheless, matter in its nature [ratio] is other than the contraries.

             The fourth point is that matter is not different but the same in number, for it exists now under one contrary and later under another.

             554. Next where he says, 'The same matter also serves . . .' (217 a 27), he explains his position from the above in this way. The matter of contraries is the same in number. But the great and the small are contraries of quantity. Therefore the matter of the great and the small is the same in number.

             This is clear in substantial change. For when air is generated from water, the same matter which formerly was under water is made to be under air, not by taking something which it did not formerly have, but rather by a reduction to act of that which was formerly in the potency of matter. The same is true when water is conversely generated from air. But there is this difference. When air is generated from water, a change from small to large occurs. For the quantity of the generated air is greater than the quantity of the water from which it was generated. However, when water is generated from air, a converse change from largeness to smallness occurs. Therefore, when a large amount of air is reduced to a smaller quantity by condensation, or when there is a change from smaller to larger by rarefaction, it is the same matter which comes to be both in act, that is, which comes to be large and small, which prior to this existed in potency.

             Therefore, condensation does not occur because some parts come together by entering into other parts, and rarefaction does not occur because connected parts are separated, as those who posit a void in bodies have thought. Rather these things occur because the matter of the same parts takes on now a larger and now a smaller quantity. Hence, to be rarefied is nothing else than for matter to take on larger dimensions by reduction from potency to act. And to be condensed is the opposite. For just as matter is in potency to determinate forms, so also is it in potency to determinate quantity. Hence rarefaction and condensation do not proceed to infinity in natural things.

             555. Next where he says, 'For as the same matter . . .' (217 a 34), he explains the same thing by examples. Since rarefaction and condensation pertain to the motion of alteration, he gives an example dealing with other alterations.

             He says that the same matter is changed from cold to hot and from hot to cold because each of these was in the potency of matter. Likewise, a thing that is hot comes to be more hot, not because some part of matter becomes hot which formerly was not hot when the body was less hot, but because all the matter is reduced to an act of greater or lesser heat.

             He gives another example dealing with the quality in quantity.

             He says that if the circumference and convexity of a larger circle is contracted to a smaller circle, it is clear that something more curved results. But this is not because circularity was made in some part which originally was not curved but straight. Rather it is because the same thing, which formerly was less curved, is now more curved.

             For in such alterations a thing does not become greater or less either by subtraction or by addition. Rather this is a change of one and the same thing from perfection to imperfection, or vice versa. This is clear because, in a thing which has a simply uniform quality, there is found no part which is without that quality. Thus, in a spark of fire, there is no part in which there is no heat or whiteness, that is, clearness. Thus, therefore, the prior heat comes to the posterior, not because some part which was not hot is made hot, but because that which was less hot becomes more hot.

             Hence also the largeness and smallness of a sensible body is not extended or amplified in rarefaction and condensation because matter takes on some addition. Rather this occurs because matter, which formerly was in potency to the great and the small, is changed from one to the other. And, therefore, rarity and density do not occur either by the addition or by the subtraction of parts which enter into each other, but rather because the matter of the rare and the dense is one.

             556. Next where he says, 'The dense is heavy . . .' (217 b 12), he explains his position by means of the effects of rarity and density. The difference of other qualities, that is, heavy and light, hard and soft, follow upon the difference of rarity and density. And thus it is clear that rarity and density diversify qualities and not quantities.

             He says, therefore, that lightness follows upon rarity, and heaviness follows upon density. And this is reasonable. For rarity results from matter receiving larger dimensions, and density results from matter receiving smaller dimensions. Thus, if we take diverse bodies of equal quantity, the one being rare and the other dense, the dense body has more matter. Moreover, it was said above in the treatment of place that the contained body is compared to the container as matter to form. And thus a heavy body, which tends toward the middle of that which is contained, is understandably more dense since it has more matter. Therefore, the circumference of a greater circle which is reduced to a smaller circle does not receive concavity in one of its parts in which concavity formerly was not, but rather that which formerly was concave is reduced to greater concavity. And also any part of fire that one might take is hot. And likewise a whole body becomes rare and dense by contraction and extension of one and the same matter, insofar as it is moved to a greater or smaller dimension.

             This is clear in those qualities which follow upon rarity and density. For heaviness and hardness follow upon density. The nature [ratio] of heaviness has been established. The nature [ratio] of hardness is also clear. For that is called hard which gives more resistance to pushing and division. And that which has more matter is less divisible, because it is less obedient to an agent, since it is more removed from act.

             And conversely, lightness and softness follow upon rarity. But in some things, for example, iron and lead, heaviness and hardness do not agree. For lead is heavier but iron is harder. The reason for this is that lead has more earthy things in it, and that which has water in it is less perfectly hardened and assimilated.

             557. Next where he says, 'From what has been said . . .' (217 b 20), he concludes to the main point.

             He says that it is clear from what has been said that there is no void separated space. Nor is there a void existing simply outside of bodies. Nor is there a void existing in the rare as void holes. Nor does a void exist in potency in a rare body, as say those who do not posit a void in bodies separated from the plenum. Thus in no way is there a void, unless one would inwardly wish to call matter a void. Matter in some way is the cause of heaviness and lightness, and thus is a cause of local motion. For density and rarity are the cause of motion in respect to the contrariety of heavy and light. But in respect to the contrariety of hard and soft they are the cause of passivity and impassivity. For the soft is that which easily undergoes division, but the hard does not, as was said. But this does not pertain to change of place, but rather to alteration.

             And thus he concludes that it has been determined how a void exists and how it does not exist.