LECTURE 5 (253 a 22-254 a 2)

THINGS MAY BE MOVED OR AT REST IN FIVE WAYS. THE FIRST TWO WAYS ARE DISMISSED

1004. The Philosopher has shown in Book VII that movers and mobile objects do not proceed to infinity. Rather there is some first. And he has just shown that motion always was and always will be. Here he proceeds further to investigate the condition of the first motion and the first mover.

             This discussion is divided into two parts. First he shows that the first motion is eternal and that the first mover is totally immobile. Secondly, where he says, 'This matter will be . . .' (260 a 20), he proceeds from this to explain the nature of the first motion and the first mover.

             The first part is divided into three parts. First he sets forth for this problem a fivefold division. Secondly, where he says, 'To maintain that . . .' (253 a 32), he dismisses three parts of this division. Thirdly, where he says, 'We have now to take . . .' (254 a 15), he asks which of the two remaining alternatives is truer. For the truth which he intends to seek depends on this.

             1005. He says, therefore, first that the beginning of the following discussion, in which we intend to investigate the first motion and the first mover, pertains to the above difficulty (which he introduced in answering the second argument); namely, does it happen that certain things are sometimes moved and sometimes at rest, and are not always moved or at rest, as a result of which motion in general is eternal.

             He says that with respect to motion and rest things must be disposed in three ways.

             One mode is that all things are always at rest and nothing is moved at any time; the second mode is that all things are always moved and nothing is at rest; the third mode is that some things are moved and some are at rest.

             But the third mode is again divided into three modes.

             The first of these is that some things are moved and some are at rest in such a way that those which are moved are always moved and those which are at rest are always at rest, and there is nothing which is sometimes moved and sometimes at rest.

             The second mode is contrary to this, namely, all things are naturally moved and at rest, and there is nothing which is always moved or always at rest.

             The third mode is a division of this second mode; namely, some things are always immobile and are never moved; others are always mobile and are never at rest; and others can be both moved and at rest so that they are sometimes moved and sometimes at rest.

             This last alternative must be determined by us as the truth, because in this is found the answers to all of the objections. When we shall have shown this, we shall have reached the end which we intend in this work; namely, we will have arrived at the first eternal motion and the first immobile mover.

             Thus the third member of the first division is divided into three parts, and there results a total of five members of this division.

             It must be noted, moreover, that in three parts of this division all beings are held to be of one disposition, as is clear in the first part, in which it was said that all things are always at rest; and in the second, in which it was said that all things are always moved; and in the fourth, in which it was said that all things are sometimes at rest and sometimes moved. In the third part beings are divided into two dispositions; namely, certain things are always moved and certain things are always at rest. In the fifth part beings are divided into three dispositions; namely, certain things are always moved, certain things are never moved, and certain things are sometimes moved and sometimes not. It must be noted that in this last part he does not mention rest, but immobility. For the first mover, which is never moved, cannot properly be said to be at rest. For, as was said in Book V, that is properly at rest which is moved naturally but is not being moved.

             1006. Next where he says, 'To maintain that . . .' (253 a 32), he dismisses three parts of the above division.

             First he shows that not all things are always at rest. Secondly, where he says, 'The assertion that . . .' (253 b 6), he shows that not all things are always moved. Thirdly, where he says, 'Nor again can it be . . .' (254 a 3), he rejects the third alternative in which it was said that things which are moved are always moved and things which are at rest are always at rest.

             Concerning the first part he makes three points.

             His first point is that it is due to a certain weakness of the intellect that some say that all things are at rest, reaching this conclusion through a sophistical argument which ignores the senses. This position arises because the intellect is not sufficient to answer sophistical arguments which contradict things which are manifest to the senses. Moreover, it is said in Topics, I, that one should not bother to argue against certain positions or problems in which one questions the need for sensation or suffering. Hence against this position it is not necessary to argue because of the folly of the speaker.

             Secondly he says that this problem concerns not some particular being, but the whole of being. And it does not pertain only to natural philosophy, but in a way it pertains to all the demonstrative sciences and to all the arts which make use of opinions, as rhetoric and dialectic. For all the arts and sciences make use of motion. The practical arts, as it were, direct certain motions, and natural philosophy speculates about the nature of motion and mobile objects. Mathematicians make use of imagined motion, saying, for example, that a moved point makes a line. And the metaphysician deliberates about first principles. Therefore, it is clear that the denial of motion is repugnant to all the sciences.

             However, an error which pertains to all beings and to all sciences is not to be disproved by the natural philosopher, but by the metaphysician. Therefore, it is not in the province of the natural philosopher to argue against this error.

             Thirdly, he says that it is not in the province of the mathematician to reject irrational and improper difficulties about the principles of mathematical doctrine. And the same is true for the other sciences. Similarly, it is not in the province of the natural philosopher to reject a position of this kind which is repugnant to his own principles. For in every science a definition of its subject is set forth as a principle. Hence in a natural science it is set forth as a principle that nature is a principle of motion. Therefore, for these three reasons it is clear that it is not in the province of natural philosophy to dispute this position.

             1007. Next where he says, 'The assertion that . . .' (253 b 6), he dismisses the second alternative in which it was stated by Heraclitus that everything is always moved.

             First he compares this opinion to the preceding one which held that everything is always at rest. He says that to maintain that everything is always moved, as Heraclitus does, is also erroneous and contrary to the principles of natural science. But this position is less repugnant to art than the first position.

             And it is clear that it is repugnant to this art. For it deprives natural science of the supposition that nature is a principle not only of motion but also of rest. And so it is clear that rest is just as natural as motion. Hence, just as the first opinion, which destroyed motion, was contrary to natural science, so also is this position, which destroys rest.

             Moreover, he says that this opinion is less contrary to this art because rest is nothing other than a privation of motion. And the point that there is no privation of motion more readily escapes notice than the point that there is no motion. For there are some slight and feeble motions which are barely sensible. And so it may seem that something is at rest which is not at rest. But large and powerful motions cannot escape notice. Hence it cannot be said that the senses are deceived in perceiving motion as they are in perceiving rest.

             Therefore, secondly, where he says, '. . . moreover the view is actually held . . .' (253 b 9), he explains how some have held this second position.

             He says that some, namely Heraclitus and his followers, have maintained that whatever exists is always moved, and not just some things, or at some time. But this motion is hidden from our senses. If they were asserting this of some motions they would be correct, for some motions are hidden from us. But since they do not designate the type of motion about which they speak, but rather they speak of all motions, it is not difficult to argue against them. For there are many motions which clearly cannot be eternal.

             1008. Thirdly, where he says, '. . . thus we may point out . . .' (253 b 13), he gives arguments against the above opinion. He does this first with respect to the motion of increase; secondly, with respect to the motion of alteration, where he says, 'Similarly, too, in the case . . .' (253 b 23), and thirdly, with respect to local motion, where he says, 'Again, in the matter of locomotion . . .' (253 b 32).

             He begins with increase because Heraclitus was especially drawn to his position from a consideration of increase. For he saw that one is increased by a small quantity in one year, and supposing that increase is continuous, he believed that in every part of that time one is increased by some of that quantity. However, this increase is not sensed because it occurs in a small part of time. And he thought that the same is true of other things which seem to be at rest.

             Aristotle argues against this by saying that it is not possible for a thing to be increased or decreased continuously such that the increased quantity is so divided with reference to time that at every moment some part of it is being increased. Rather after the increase of one part there is an intermediate time in which nothing is increased and in which there occurs a disposition for the increase of the next part.

             He clarifies this with examples. First, we see that many raindrops erode a stone. Secondly, we see that plants growing in stones divide the stones.

             If many raindrops wear off or carry away so much of a stone in so much time, we cannot say that earlier in half the time half of the raindrops carried off half of this quantity. For what happens here is the same as that which occurs in dragging a boat. For if a hundred men drag a boat over so much space in so much time, it does not follow that half of them will move the boat through half of the space in the same time, or through the same space in twice the time, as was said in Book VII. Likewise, if many raindrops erode a stone, it does not follow that some part of these raindrops earlier removed half as much in some time.

             The reason for this is that that which is removed from the stone by the many raindrops is divisible into many parts. Nevertheless, none of these many parts is removed from the stone separately. Rather all the parts are removed together insofar as they are in potency in the removed whole.

             He speaks here about the first part which is removed. The fact that a large quantity was removed from the stone by the raindrops over a long period of time does not prevent some part from being removed earlier by part of the raindrops. Nevertheless one must arrive at some removed quantity which is removed as a whole and not part after part. In the removal of that whole, therefore, none of the preceding raindrops removed anything. Rather they disposed a certain amount for removal. The last raindrop acts in virtue of all when it removes that which the others disposed for removal.

             The same is true of decrease. If a thing decreases a certain amount in a certain time, it is not necessary to say that in every part of that time some of that quantity is subtracted, even though that quantity be divided to infinity. Rather at some time a whole will go away at once. And the same is true of increase. Hence it is not necessary that a thing be increased or decreased continuously.

             1009. Next where he says, 'Similarly, too, in the case . . .' (253 b 23), he opposes the above position with respect to alteration. He gives three arguments.

             First he says that what was asserted about increase must also be said of any alteration. For although a body which is altered is infinitely divisible, nevertheless because of this it is not necessary that the alteration be divided to infinity such that in every part of time some of the alteration occurs. Frequently alteration occurs swiftly such that many parts of the altered body are altered together, as occurs in the jelling or congealing of water. For some whole of the water is congealed at one time, and not part after part. (If, however, a large amount of water is given, nothing prevents it from congealing part after part.)

             It should be noted that what is said here about alteration and increase seems to be contrary to what was said in Book VI, where it was shown that motion is divided according to the division of time and of the mobile object and of the thing with respect to which there is motion.

             But it must be understood that in Book VI Aristotle was treating motion in general, and was not applying his remarks to any mobile objects. Therefore, what he treated there about motion concerns the requirements for the continuity of motion. Here, however, he is speaking of the application of motion to determinate mobile objects in which it happens that a motion, which could be continuous according to the common nature [ratio] of motion, is interrupted and is not continuous.

             1010. He gives the second argument where he says, 'Again, when anyone has fallen ill . . .' (253 b 28).

             He says that if someone who is ill is to be cured, he must be cured in some time and not in an instant. And it is further necessary that the mutation of being cured tend toward a definite terminus, namely, to health and to nothing else. Therefore, every alteration requires a determined time and a determined terminus (because every alteration is to a contrary, as was said in Book V . But no mutation of this kind is always continuous. Hence, to say that something is altered always and continuously is to doubt the obvious.

             1011. He gives the third argument where he says, 'Moreover, we notice . . .' (253 b 30). He says that even over a long period of time a stone does not become harder or softer. Hence it is foolish to say that all things are always altered.

             1012. Next where he says, 'Again, in the matter of locomotion . . .' (253 b 32), he opposes in two ways the above opinion in respect to local motion. First he states that some local motions and states of rest are so obvious that they cannot go unnoticed. It would be strange indeed if a stone which is thrown downward or which rests on the ground would go unnoticed. Hence it cannot be said that all things are always moved locally because local motion is unnoticed.

             1013. Secondly, where he says, 'Further, it is a law . . .' (253 b 33), he reasons as follows. Earth and every other natural body are at rest from the necessity of nature when they are in their proper places, and they are removed from their proper places only by force. But it is clear that some natural bodies are in their proper places. It must be said, therefore, that some things are at rest with respect to place, and not all things are moved locally.

             Finally he concludes that from the foregoing and other similar arguments one can come to know that it is impossible either for all things to be always moved, as Heraclitus maintained, or for all things to be always at rest, as Zeno and Parmenides and Melissus asserted.