LECTURE 4 (226 a 23-b 18)

HE CONCLUDES THAT THERE IS MOTION ONLY IN QUANTITY, QUALITY, AND WHERE. HE EXPLAINS HOW THERE IS MOTION IN THESE THREE GENERA AND WHAT HE MEANS BY 'IMMOBILE'

             678. Having shown that there is no motion in substance, or in relation, or in action and passion, he indicates in what genera there is motion.

             Concerning this he makes three points. First he states his intended conclusion. Secondly, where he says, 'Motion in respect of Quality . . .' (226 a 26), he explains how there is motion in each of the three genera. Thirdly, where he says, 'Change within the same kind . . .' (226 b 1), he answers a difficulty.

             He says, therefore, first that since there is no motion in substance, or in relation, or in action or passion, as was shown, it follows that there is motion in only three genera, that is, in quantity, quality, and where. For in each of these genera there is contrariety, which is required by motion.

             For this reason he omits three genera, namely, when, site, and state. And it was shown above how there is contrariety in the three genera in which there is motion.

             679. Next where he says, 'Motion in respect of Quality . . .' (226 a 26), he explains how there is motion in the above mentioned genera.

             First he explains how there is motion in quality; secondly, in quantity, where he says, 'Motion in respect of Quantity . . .' (226 a 30); and thirdly, in where, where he says, 'Motion in respect of Place . . .' (226 a 33).

             He says, therefore, first that motion in quality is called alteration.

             The common name 'alteration' refers to this genus because that which differs in quality is customarily called 'other' (alterum). We do not speak of quality here as referring to that which is found in the genus of substance, according to which a substantial difference is said to be predicated as a quality. Rather we speak of passive quality, which is contained in the third species of quality. In this sense quality is said of something done or not done, like hot and cold, white and black, and such things. For in these things there is alteration, as will be proven in Book VII.

             680. Next where he says, 'Motion in respect of Quantity . . .' (226 a 30), he explains how there is motion in quantity.

             He says that motion in quantity is not named according to its genus, as alteration is. Rather it is named according to its species, which are increase and decrease. Motion from imperfect to perfect magnitude is called increase. And motion from perfect to imperfect magnitude is called decrease.

             681. Next where he says, 'Motion in respect of Place . . .', he shows how there is motion in where.

             He says that motion in respect to place does not have a name which is common to the genus, nor a name which is proper to the species. Rather the general name 'bringing forth' is applied to it, even though this name is not altogether proper to local motion in general. For only those things which are so moved in respect to place that they do not have the power to stand still are properly said to be 'brought forth'. Such things are not moved in respect to place by themselves, but by something else.

             Therefore, a common name can be applied to motion in quality because qualities are contraries in respect to the proper nature [ratio] of their species. And because of this they are contained under the genus of quality. But in quantity there is no contrariety in respect to the nature [ratio] of its species, but in respect to the perfect and the imperfect, as was said above. And according to this the species are named. And there is contrariety in place only by comparison to a motion in which two termini are at maximum distance. Therefore, since this contrariety refers to something altogether extraneous to this genus, motion in this genus cannot have a name either in general or in respect to its parts.

             682. Next where he says, 'Change within the same kind . . .' (226 b 1), he points out that there could be a difficulty in showing to what species of motion is reduced mutation in respect to more and less. An example would be something becoming less white from more white, and vice versa. One might think that this should be reduced to the motion of increase and decrease. But he shows that this is reduced to the motion of alteration. He says that a mutation of either more or less which is in a species of quality, for example, in whiteness, is an alteration.

             He proves this by the fact that alteration is a mutation from contrary to contrary in respect to quality. This happens in two ways: either simply, as when someone is changed from white to black or vice versa; or in a qualified way, as when something is changed from more white to less white or vice versa.

             That to be changed in a qualified way is to be changed from contrary to contrary he proves as follows. When a thing is changed from more white to less white, it can be said to be changed from contrary to contrary because it approaches the contrary, that is, black. But when a thing is changed from less white to more white, it is the same as if it were changed from contrary to contrary, that is, from black to white itself. For it becomes more white because it recedes more from black and participates more perfectly in whiteness.

             In respect to alteration it makes no difference, except as follows, whether a thing is changed from contrary to contrary either simply or in a qualified way. When a thing is changed simply from contrary to contrary, the termini of the alteration must be two contraries in act, for example, white and black. But mutation of more and less occurs insofar as there is or is not more or less of one of the contraries.

             Lastly, where he says, 'It is now clear . . .' (226 b 9), he concludes that it is clear from the above that there are only three species of motion.

             683. Next where he says, 'The term "immovable" . . .' (226 b 10), he explains the ways in which 'immobile' is predicated. He gives three ways.

             First, that is said to be immobile which in no way can be moved, for example, God. In a similar way that is said to be invisible which cannot be seen, for example, sound.

             Secondly, that is said to be immobile which is moved with difficulty. This occurs in two ways: either because, after a thing begins to be moved, it is moved slowly and with great difficulty, as when one says a lame man is immobile; or because a thing is difficult to begin to be moved, and it is necessary to work at this for a long time, as when we say that a mountain or a large rock is immobile.

             Thirdly, that is said to be immobile which can be moved and moved easily, nevertheless it is not being moved when it can, and where it can, and how it can be moved. Only such an object is properly said to be at rest, for rest is the contrary of motion. He takes contrariety here in a wide sense such that it also includes privation. Hence he concludes that rest must be a privation in that which is susceptible of motion. For a contrary and a privation are only in that which is susceptible of an opposite.

             Finally, where he says, 'The foregoing remarks . . .' (226 b 17), he concludes his remarks by saying that it is clear from the above what motion is, and what rest is, and how many mutations there are, and which mutations can be called motions.