Commentary Aristotle Physics
Lecture 3
There is no motion per se in the categories other than quantity, quality, and place
If, then, the categories are severally distinguished as substance, quality, where, time, relation, quantity, and activity or passivity, then it necessarily follows that there are three kinds of motion—qualitative, quantitative, and local.
In respect of substance, there is no motion, because substance has no contrary among things that are.
Nor is there motion in respect of relation, for it may happen that, when one correlative changes, while the other does not itself change, it is no longer applicable, such that, in these cases the motion is accidental.
Nor is there motion in respect of agent and patient—in fact, there can never be motion of mover and moved, because there cannot be motion of motion or generation of generation or in general change of change.
For in the first place, there are two senses in which motion of motion is conceivable.
The motion of which there is motion might be conceived as subject; for instance, a man is in motion because he changes from fair to dark. Can it be that, in this sense, motion grows hot or cold, or changes place, or increases or decreases? This is impossible, since change is not a subject.
Or can there be motion of motion in the sense that some other subject changes from a change as of a terminus, for instance, as a man changes from falling ill to getting well? Even this is possible only in an accidental sense.
For whatever the subject may be, motion is change from one form to another. (And the same holds good of generation and corruption, except that, in these processes, we have a change to a particular kind of opposite, while the other, motion, is a change to a different kind.)
So, if there is to be motion of motion, that which is changing from health to sickness must simultaneously be changing from this very change to another.
It is clear, then, that, by the time that it has become sick, it must also have changed to whatever may be the other change concerned (for that it should be at rest, though logically possible, is excluded by the theory).
Moreover, this other can never be any contingent change, but must be a change from something definite to some other definite thing.
So, in this case, it must be the opposite change, namely, convalescence.
It is only accidentally that there can be change of change: for instance, there is a change from remembering to forgetting only because the subject of this change changes at one time to knowledge, and at another to ignorance.
In the second place, if there is to be change of change and generation of generation, we shall have an infinite regress. Thus, if one of a series of changes is to be a change of change, the preceding change must also be so:
for instance, if simple generation was ever in process of generation, then that which was generating simple generation was also in process of generation, such that we should not yet have arrived at what was in process of simple generation, but only at what was already in process of generation in process of generation.
And this again was sometime in process of generation, such that, even then, we should not have arrived at what was in process of simple generation. And, since in an infinite series there is no first term, here there will be no first stage, and therefore no following stage to be had either. On this hypothesis, then, nothing can become or be moved or change.
Third, if a thing is capable of motion, it is also capable of the contrary motion or coming to rest, and what is capable of generation is also capable of corruption.
Consequently, if there be generation of generation, when what comes to be comes to be, it is in process of corruption when it has reached the stage of generation, for it cannot be in process of corruption when it is just beginning to become or after it has ceased to become, for that which is in process of corruption must be in existence.
Fourth, there must be a substrate underlying all processes of generation and changing. What can this be in the present case? It is either the body or the soul that undergoes alteration: what is it that correspondingly becomes motion or generation? And, again, what is the goal of their motion? It must be the motion or generation of something from something to something else.
But in what sense can this be so? For the generation of learning cannot be learning, and so neither can the generation of generation be generation, nor can the generation of any process be that process.
Finally, since there are three kinds of motion, the substratum and the goal of motion must be one or other of these—for instance, locomotion will have to be altered or to be locally moved.
To sum up, then, since everything that is moved is moved in one of three ways, either accidentally, or partially, or essentially, change can change only accidentally—as, for instance, when a man who is being restored to health runs or learns—and accidental change we have long ago decided to leave out of account.
660. After dividing change into generation, corruption, and motion, the Philosopher now subdivides motion into its parts.
And, because it is the same science that deals with a thing and with its opposite, he first gives the species of motion;
second, he explains the various senses of “immobile,” at the term “immobile” (226b10; [603]).
About the first, he does two things:
first, he posits a conditional proposition in the light of which he deduces the parts of motion;
second, he explains this conditional proposition, at “in respect of substance” (225b10; [662]).
661. Therefore, he concludes (225b5) from the previous lecture that, since motion goes from subject to subject, and subjects are involved in certain genera of the predicaments, the species of motion must be distinguished according to the genera of predicaments, especially since motions derive their nature and name from the terminus, as was said above. Therefore, if the predicaments are divided into ten genera of things—substance, quality, and the rest (as is explained in the Categories and in Metaphysics 5)—and motion is found in three of these genera, there must be three species of motion, that is, in the genus of quantity and in the genus of quality and in the genus of where, which is said in respect of place.
The way in which motion is present in these three genera, as well as how it is related to the predicaments of action and passion, has been explained in book 3. Hence it is enough to mention briefly that a motion is in the same genus as its terminus, not that the motion itself would be in the genus—for example, of quality—but it is placed there by reduction.
For just as potency is reduced to the same genus as its act, inasmuch as every genus is divided by potency and act, so it is necessary for motion, which is an imperfect act, to be reduced to the genus of its perfect act.
But, when motion is regarded as being in something, though originating from something else, or as originating from one thing and being in something else, then it belongs to the predicaments of action and passion.
662. Then, at “in respect of substance” (225b10), he explains the conditional proposition:
first, he shows that there is no motion in any but the three genera mentioned;
second, he shows how motion is present in those three genera, at “since, then, motion can belong” (226a23; [678]).
About the first, he does three things.
First, he shows that motion is not in the genus of substance;
second, that it is not in the genus of relation, at “nor is there motion in respect of relation” (225b11; [666]);
third, that it is not in the genera of action and passion, at “nor is there motion in respect of agent and patient” (225b13; [668]).
He passes over the three predicaments of when, position, and habit. For “when” expresses existence in time, which is the measure of motion. Hence, for the same reason that there is no motion in action and passion, which pertain to motion, there is no motion in when. Position denotes order of parts, and order is a relation; in like manner, habit bespeaks a relationship existing between a body and what is adjacent to it. Hence, there can be no motion in position and habit any more than in relation.
That motion (225b10) is not found in the genus of substance he proves by saying that every motion is between contraries, as we have said; but nothing is contrary to substance. Therefore, there is no motion in respect of substance.
663. Now, there seems to be a disagreement between this doctrine of the Philosopher and what he says in De generatione et corruptione, that fire is contrary to water. And, again, in De caelo, he says that the heaven is capable neither of coming to be nor of ceasing to be, because it does not have a contrary—which seems to imply that things that cease to be are either contrary or composed of contraries.
To reconcile this, some assert that one substance can be contrary to another, as fire to water, in respect to form but not in respect to their subject. But if that were so, Aristotle’s proof would be worthless, for then there would be motion in substance as long as the substantial forms were contrary. For motion is from form to form, because, even in alteration, subject is not contrary to subject, but form to form.
Consequently, another explanation must be given: fire is contrary to water in respect of their active and passive qualities—which are hot and cold, wet and dry—but not in respect of their substantial forms. It cannot be said that heat is the substantial form of fire, for in other bodies, it is an accident in the genus of quality, and substance cannot be an accident of something.
But, even this answer presents a difficulty. It is clear that properties originate from the principles of the subject, that is, from matter and form. Now, if the properties of fire and water are contrary, then, since the causes of contraries are themselves contrary, it seems that the substantial forms are contrary. Moreover, it is proved in Metaphysics 10 that every genus is divided by differences that are contrary, and differences are traced to the forms, as Metaphysics 8 explains. Therefore, it seems that there is contrariety between substantial forms.