LECTURE 15 (261 a 28-b 26)

ONLY LOCAL MOTION CAN BE CONTINUOUS AND ETERNAL

1097. After the Philosopher has shown that local motion is the first among all motions, he shows here which local motion is first.

             And since, as was said above, the first motion must be continuous, this discussion is divided into two parts. First he shows which motion can be always continuous. Secondly, where he says, 'It can now be shown . . .' (265 a 13), he shows that that motion is first.

             The first part is divided into three parts. First he shows that only local motion can be continuous. Secondly, where he says, 'Let us now proceed . . .' (261 b 27), he shows that no local motion other than circular motion can be continuous. Thirdly, where he says, 'On the other hand . . .' (264 b 9), he shows that circular motion is continuous.

             Concerning the first part he makes two points. First he states his intention. Secondly, where he says, 'Every other motion . . .' (261 a 32), he proves his position.

             He says, therefore, first that since it has been shown that local motion is the first among all the species of motion, it must now be shown which local motion is first. For, as was explained in Book VII, there are many species of local motion.

             And the same method, that is, the same consideration, will also clarify what we have just said and what we have previously assumed at the beginning of Book VIII; namely, there is a motion which is continuous and eternal. For the first motion and continuous motion must be the same, as was shown above. Therefore, both of them fall within the same consideration. Hence, from what will be said it is clear that no species of motion other than local motion can be continuous and eternal.

             1098. Next where he says, 'Every other motion . . .' (261 a 32), he proves his position.

             Concerning this he makes two points. First he shows that no species of motion other than local motion can be continuous and perpetual, existing as one and the same. Secondly, where he says, 'Furthermore, in the case . . .' (261 b 22), he shows that no two opposed mutations can succeed each other without an intervening state of rest.

             Concerning the first part he makes two points. First he proves his position. Secondly, where he says, 'The question whether . . .' (261 b 7), he refutes objections.

             Concerning the first part he makes two points. He proves his position first in regard to motions, and secondly in regard to mutations, where he says, 'And we have a similar . . .' (261 b 3).

             He proposes, therefore, first a proposition which is commonly true of both motion and mutation; namely, every motion and mutation is from an opposite to an opposite. But local motion is in a certain way excluded from this general truth, as was said at the end of Book VI. For generation and corruption, which are mutations, have as their termini being and non-being. The opposed termini of alteration are contrary passions, that is, passive qualities, like hot and cold, white and black. The opposed termini of increase and decrease are the great and the small, or the perfect and the imperfect in magnitude or quantity.

             It is clear, moreover, from what was said in Book V, that motions to contraries are contraries. Therefore, the contrary of a motion to white is a motion to black. But contraries cannot exist together. Hence, while a thing is being moved to white, it is not at the same time being moved to black. What begins to be moved from white to black by a motion of blackening, even though it was moved by a whitening motion while it was becoming white, clearly cannot be moved at the same time by a blackening motion. However, that which existed previously, but was not always moved by some determined motion, must be said to have been previously at rest with a rest opposed to this motion. For everything which can be moved naturally is either at rest or in motion. It is clear, then, that that which is moved to a contrary was at one time at rest with a rest opposed to such a motion. Therefore, no motion which is to a contrary can be continuous and eternal.

             If to this conclusion is added what was stated at the beginning, namely, every motion of alteration or of increase or of decrease is to some contrary, it will follow that no such motion can be continuous and eternal.

             1099. Next where he says, 'And we have a similar . . .' (261 b 3), he shows that the same is true of mutations, that is, of generation and corruption. For generation and corruption are opposed both universally in respect to the common opposition of being and non-being and singularly, for example, the generation of fire is opposed to the corruption of fire in respect to the opposition of its being and non-being.

             Hence, if it is impossible for opposed mutations to exist together, it follows that no mutation can be continuous and eternal, just as was said above about motions. It is necessary, therefore, for an intermediate time in which there is corruption to be interposed between two generations of the same thing. And likewise between corruptions there is a time of generation.

             1100. Next where he says, 'The question whether . . .' (261 b 7), he refutes three objections. The first is that someone might say that mutations are opposed according to the opposition of their termini. But the termini of generation and corruption are not contraries, but contradictories. Hence, it seems to follow that generation and corruption are not contraries. And thus the same argument cannot be applied to them and to motions which are contraries.

             He answers this objection by saying that it makes no difference whether or not mutations which differ according to contradictory termini are contraries. It must only be true that it is impossible for them both to be in the same thing at the same time. Whether or not they are contraries is irrelevant to the argument.

             1101. He refutes the second objection where he says, 'Nor does it matter . . .' (261 b 10).

             Someone may say that what is not always moved must be previously at rest, because motion is opposed to rest. But this does not apply to the mutations of generation and corruption to which, properly speaking, rest is not opposed, as was said in Book V.

             He answers this objection by saying that it makes no difference in the argument if it is not necessary for there to be rest in one of the contradictory termini. Nor does it make any difference if mutation is not opposed to rest (for, perhaps, that which does not exist cannot be at rest: corruption, however, is to non-being: and so it seems that there cannot be rest in the terminus of corruption). It is sufficient for the proof if it is true that there is an intermediate time between two generations or between two corruptions. For then it follows that neither of these mutations is continuous.

             After this he returns to the first objection and says that it does not matter with respect to contradictory mutations whether they be contraries or not. For not even in the earlier discussion about motions did it matter whether there is contrariety in them but only that they do not exist together. This is not peculiar to contraries, but it is common to all opposites.

             1102. He refutes the third objection where he says, 'And there is no need . . .' (261 b 15).

             He has said above that motions to contraries are contraries. Since, then, motion is contrary to rest, it seems to follow that one thing has two contraries, which is impossible, as was proven in Metaphysics, X.

             In rejecting this he says that there is no need to be disturbed because it seems to follow that the same thing is contrary to many, namely, motion is contrary to both rest and to the contrary motion. But we need to realize that one contrary motion is in a way opposed both to its contrary motion and to rest--to the contrary motion according to direct contrariety, but to rest according to the opposition of privation. This latter shares in contrariety insofar as the opposed rest is the end and the completion of the contrary motion. For example, the equal and the commensurable is in a way opposed both to that which excels and to that which is excelled, or to the great and the small, to which it is opposed in respect to the privation, as is clear in Metaphysics, X. And again it is necessary to realize that opposite motions and opposite mutations do not occur together.

             1103. Next where he says, 'Furthermore, in the case . . .' (261 b 22), he shows that not only between two motions or mutations of the same species must there be an intermediate time, and that no one mutation which is to an opposite can be eternal and continuous, but also it is impossible for opposed motions or mutations to so succeed themselves that there is no intervening time. For it seems to be completely inconsistent with generation and corruption to say that when a thing has come to be and the generation has been completed, then corruption must begin at once and that what has been generated does not remain for any period of time. For a thing would be generated in vain unless that which is generated remains in existence.

             From these mutations conclusions about the others can be drawn. For since nature always operates in the same way, it is natural for the other cases to be the same. And just as it seems to be inconsistent that what is generated immediately is corrupted as soon as it is generated, so it seems to be inconsistent that as soon as a white thing has been made white, it begins to become black, and what is increased immediately begins to decrease. For in all these cases the purpose of nature would be frustrated.