BOOK VIII

Lecture 1

Opinions on the beginning and end of motion

965. After showing in the preceding book that it is necessary to posit a first mobile, and a first motion, and a first mover, the Philosopher intends in this present book to inquire after a description of the first mover, and first motion, and first mobile, The book is divided into two parts:

In the first he premisses something necessary to the following investigation, namely, that motion is sempiternal;

In the second he proceeds to investigate what is proposed, (L. 5).

About the first he does three things:

First he raises a problem;

Secondly, he states the truth according to his own opinion, (L. 2);

Thirdly, he answers possible objections to the contrary, (L. 4)#

In regard to the first he does three things:

First he proposes his problem;

Secondly, he gives opinions for both sides, at 968;

Thirdly, he shows the usefulness of this consideration, at 970.

About the first he does two things:

First he proposes the problem he intends to investigate;

Secondly, he responds to a tacit question, at 967.

966. In regard to the first it should be known that Averroes says that Aristotle in this book does not intend to inquire whether motion is sempiternal universally, but limits his question to the first motion.

But if one considers both the words and procedure of the Philosopher, this is entirely false. For the words of the Philosopher speak of motion in a universal sense. He says in effect: “Was there ever a becoming of motion before which it had no being and is it perishing again so as to leave nothing in motion?” From this it is clear that he is not inquiring about one definite motion but about motion universally, asking whether at any time there was no motion.

The falseness of Averroes’ statement appears also from the very procedure of Aristotle. First, it is Aristotle’s custom always to argue to his proposition from proper causes. Now, if anyone will consider the arguments he adduces, he will see that in none of them does Aristotle argue from a middle term that refers properly to the first motion, but he argues rather from a middle proper to motion in general. Hence this alone shows that he intends to inquire here about the sempiternity of motion in general.

Secondly, if he had already proved that there is one or a number of sempiternal motions, he would have been foolish to ask below whether anything is eternally in motion, for that question would have been already answered. It also is ridiculous to say that Aristotle would repeat from the start his consideration of a problem he had already settled, and act as though he had omitted something, as the Commentator pretends. For Aristotle had the opportunity to correct his book and fill in at the proper place any section he had omitted, so as not to proceed in a disorderly way. For if this chapter had been treated in the way charged by the Commentator, everything that follows would be confused and disorderly. This is not strange, for, having supposed an initial impossibility, others then follow.

Furthermore, the correctness of our view is shown by the fact that Aristotle later on uses what he proves here, as a principle to prove the eternity of the first motion. He would never have done this, had he already proved that the first motion is eternal.

The reason which moved Averroes is wholly frivolous. For he says that if Aristotle is here intending to inquire into the eternity of motion in common, it will follow that the consideration of Aristotle has been diminished, because it is not evident from what he proves in this place, how motions could be always continued one to the other.

But this has no weight, because it is enough for Aristotle to prove in this chapter in a general way that motion has always been. But how the eternity of motion is continued—whether it is because all things are always in motion, or because all things are sometimes in motion and sometimes at rest, or because some things are always in motion and others sometimes in motion and sometimes at rest—is a question he raises immediately after the present one.

Thus the present chapter must be explained according to this intention, namely, that he intends to inquire about motion in common. According to this, therefore, he asks: “Did motion in common begin to be at some time, so that previously there had never been any motion, and so that at some time it will perish so as to leave nothing in motion, or, on the other hand, did it never begin and will it never cease, so that it always was and always will be?

And he gives an example taken from animals, for some philosophers have said that the world is a certain large animal. For we see animals as alive so long as motion is apparent in them, but when all motion ceases in them they are said to be dead. Accordingly, motion in the whole universe of natural bodies is taken as a kind of life. If, therefore, motion always was and always will be, then this sort of life of natural bodies will be immortal and never-failing.

967. Then at (749) he answers a tacit question. For in the preceding books Aristotle had discussed motion in common, without applying it to things; but now, inquiring whether motion has always existed, he applies his general doctrine about motion to the existence it has in things. Therefore, someone could say that in this consideration the first question should have been about whether motion has existence in things rather than whether it is eternal, especially since there are some who have denied that motion exists.

To this he responds that all who have spoken about the nature of things admit that motion exists. This is evident from their statements that the world was made, and from their consideration of the generation and ceasing-to-be of things, which cannot occur without motion. It is therefore a common supposition in natural science that motion has existence in things. Hence there is no need to raise this question in natural science any more than in other sciences are raised questions about the suppositions of the science.

968. Then at (750) he presents opinions for both sides of the question he proposed.

First he gives the opinions which declare that motion is eternal;

Secondly, those who declare that motion is not eternal, at 969.

In explanation of the first part (750), therefore, it should be known that Democritus supposed that the first principles of things are bodies that are per se indivisible and always mobile and that the world came to be by the chance aggregation of these bodies—not only the world in which we exist but an infinitude of other worlds, since these bodies congregated to form worlds in diverse parts of infinite void. Still he did not posit these worlds as fated to endure forever; rather, some came into existence as a result of atoms combining, and others passed out of existence as a result of the same atoms scattering. Therefore all the philosophers who agree with Democritus assert the eternity of motion, because they say that the generation and ceasing-to-be of certain worlds i’s always going on-and that necessarily involves motion.

969. Then at (751) he gives the opinions of the other side. And he says that whoever declare that there is just one world which is not eternal, also declare what reasonably follows with respect to motion, namely, that it is not eternal.

Therefore, if there be supposed a time in which nothing was in motion, this could happen in two ways, just as it is in two ways that this world could be supposed not always to have been: in one way, that this world began in such a way that previously it never existed at all, as Anaxagoras held; in another way, that the world so began to be that it did not exist for some time previously, but that it again had existed before that time, as Empedocles held.

In like manner with respect to motion, Anaxagoras said that at one time all things were a mixture of one thing with another and nothing was segregated from anything else—in which mixture it was necessary to posit that all things were at rest, for motion does not occur without separation, since whatever is in motion separates from one terminus in order to tend to another. Therefore Anaxagoras posited the pre-existence of this mixture and rest in infinite time, in such a way that at no time before (the present world) had there been any motion at all, and that it was Mind, which alone was unmixed, that caused motion in the first instance and began to separate things one from another.

Empedocles, on the other hand, said that in one period of time some things are in motion, and again in another period all things are at rest. For he posited Friendship and Discord as the first movers of things: Friendship’s property was to make a unity of all things, and Discord’s to make many things from the one. But because the existence of a mixed body requires a mingling of the elements so as to form one thing, whereas the existence of a world required that the elements be dispersed in orderly fashion, each to its respective place, he posited that Friendship is the cause of the coming-to-be of mixed bodies, and Discord the cause of their ceasing-to-be; but that, contrariwise, in the whole world Friendship was the cause of its ceasing-to-be and Discord the cause of its coming-to-be.

Accordingly, he posited that the whole world is being moved, when either Friendship makes one from the many or when Discord makes many of the one; but during the intermediate times, he supposed there was rest—not in the sense that there was no motion at all, but none with respect to the general change of the world.

Because Aristotle had mentioned the opinion of Empedocles, he also gave the very words, which are difficult to interpret because they are in metre.

Thus, therefore, did Empedocles express his opinion in this arrangement of words : “It has learned to be born,” i.e., it is customary for something to be generated, “the one from the manifold”; “and again,” i.e., in another way, “from the one commingled,” i.e., composed of a mixture, “the manifold arises,” i.e., the many come to be through separation—for some things are generated by combining with others, and others by separating.

And according to what we observe in regard to particular instances of coming-to-be, so “thus do things come to be,” i.e., the same must be understood in the universal coming-t-o-be of things with respect to the whole world. “Nor is their era one,” i.e., there is not just one period of duration of things; but at one time a world is generated, at another it is destroyed, and in between there is rest: for “era” is taken to mean the measure of the duration of a thing..

He expresses the distinction of these eras when he adds, “Thus are they changed,” i.e., as though stating that the time in which things pass through the cycle of combining or separating is called one era. And lest anyone suppose that the generation of a world does not require an era, i.e., a period of time, but that the universe comes to be in an instant, Empedocles adds, “nor are they made perfect all at once,” but after a long interval of time.

Then speaking of the other era he adds, “thus are they always immobile,” i.e., in the time between the generation and corruption cycle, he supposed that things are at rest.

And lest anyone believe that before there was always change, and that later there will be continual rest, he excludes this by saying “alternately,” i.e., as though saying that this happens in cycles, namely, that things change and then rest, and then change again, and so on ad infinitum.

Then the words of Aristotle are added to explain the foregoing words of Empedocles, especially the expression, “thus they change.” He says therefore that following the words, “thus they change,” must be understood the addition, “from then hence,”, i.e., from a definite beginning up to the present—not in the sense that motion always was, or that after it began it had been interrupted.

970, Then at (752) he shows the usefulness of considering the question he has proposed. And he says that we must consider just what is the truth about this question, for to know the truth about it is most necessary not only for natural science but the science of the first principle as well, since both here and in the Metaphysics he uses the eternity of motion to prove the first principle.

This method of proving the existence of a first principle is most efficacious and irresistible. For if on the supposition that both motion and the world existed forever, it is necessary to posit one first principle, then, if the eternity thereof should be rejected, it is all the more necessary, for it is clear that every new thing requires a principle bringing it into being. Now the only reason why it could seem that no first principle would be necessary, would be if things were ab aeterno. But if the existence of a first principle follows even on that supposition, i.e., that the world existed ab aeterno, it is clear that the existence of a first principle is absolutely necessary.

Lecture 2

Arguments for the eternity of motion

971. After raising the problem of the eternity of motion, the Philosopher now intends to show that motion is eternal. His treatment is divided into two parts:

In the first he explains his proposition;

In the second he solves objections contrary to his proposition, (L.4).

About the first he does two things:

First he presents arguments to show the eternity of motion;

Secondly, he answers opinions to the contrary, (L. 3).

About the first he does two things:

First he shows that motion always has been;

Secondly, that it always will be, at 895.

About the first he does two things:

First he explains his proposition with an argument from motion;

Secondly, with an argument from time, at 979.

About the first he does three things:

First he premisses something needed for his proposition;

Secondly, he presents a proof that manifests his proposition, at 976;

Thirdly, he shows that his argument proceeds necessarily, 977,

972. He says first (753) therefore, that in order to demonstrate the proposition we must begin with things determined at the very beginning of the Physics and use them as principles. By this he gives us to understand that the preceding books, in which he determined about motion in general and which for this reason are given the general title “About Natural Things,” are set off from this Book VIII, in which he begins to apply motion to things.

He assumes, therefore, what was said in Physics III, namely, that motion is the act of a mobile precisely as such. From this it appears that in order for motion to exist there must exist things which can be moved with some sort of motion, because an act cannot exist without the thing of which it is the act. Accordingly, from the definition of motion it is evident that there must be a subject of motion, if there is to be motion at all.

But even without the definition of motion that fact is per se evident from the general consent of all, for everyone admits as a necessary fact that nothing is moved except what can be moved—and this with reference to any and all motion; for example, nothing can be altered except what is alterable, or be moved with respect to place unless it be changeable with respect to place.

And because the subject is by nature prior to what is in the subject, we can conclude that in individual changes—both from the viewpoint of the mobile and of the mover—the combustible subject is prior to its being set afire, and the subject capable of setting it afire is prior to its setting afire, prior, I say, not always in time but in nature.

973. From this argument of Aristotle, Averroes took occasion to speak against what is held by faith about creation. For if coming-to-be is a kind of change and every change requires a subject, as Aristotle here proves, it is necessary that whatever comes to be does so from a subject, therefore, it is not possible for something to come to be from nothing.

He confirms this with another argument: When it is said that the black comes to be from the white, this is not to speak per se, in the sense that the white itself is converted into the black, but it is to speak per accidens, in the sense that upon the departure of the white, the black succeeds it. Now whatever is per accidens is reduced to what is per se. But that from which something comes to be per se, is the subject, which enters into the substance of what comes to be. Therefore, whatever is said to come to be from its opposite comes to be from it per accidens, but per se it comes to be from the subject. Accordingly, it is not possible for being to come to be from non-being absolutely.

In further support of his position Averroes adduces the common opinion of the early philosophers that nothing comes to be from nothing.

He also gives two reasons from which he considers that the position arose that something should come to be from nothing. The first is that ordinary people do not consider as existing anything but what is comprehensible by sight; therefore, because they see something visible come to be which previously was not visible, they think that it is possible for something to come to be from nothing.

The second reason is that among the common people it could be thought to be a weakening of the virtue of the agent that it should need matter in order to act, which condition, however, does not derive from the impotency of the agent, but from the very nature of motion. Therefore, because the first agent does not have a power which is in any way deficient, it follows that it should act without a subject.

974, But if one considers rightly, he was deceived by a cause similar to the cause by which he claimed we are deceived, namely, by considering particular things. For it is clear that a particular active power presupposes the matter which a more universal agent produces, just as an artisan uses the matter which nature makes. From the fact therefore, that every particular agent presupposes matter which it does not produce, one should not suppose that the first universal agent—which is active with respect to all being—should presuppose something not caused by it.

Nor, moreover, is this in keeping with the intention of Aristotle who in Metaphysics II proves that the supremely true and the supreme being is the cause of being for all existents. Hence the being which prime matter has—i.e., a being in potency—is derived from the first principle of being which is in a supreme way a being. Therefore, it is not necessary to presuppose for its action anything not produced by it.

And because every motion needs a subject—as Aristotle proves here, and as is the truth of the matter—it follows that the universal production of being by God is neither motion nor change, but a certain simple coming forth. Consequently, “to be made” and “to make” are used in an equivocal sense when applied to this universal production of being and to other productions.

Therefore, just as, if we should understand the production of things to be from God ab aeterno—as Aristotle supposed, and a number of the Platonists—it is not necessary, indeed, it is impossible, that there have been a pre-existing but unproduced subject of this universal production, so also, in accord with the tenets of our faith, if we posit that he did not produce things ab aeterno but produced them after they had not existed, it is not necessary to posit a subject for this universal production. It is evident, therefore, that what Aristotle proves here, namely, that every motion requires a mobile subject, is not against a tenet of our faith—for it has already been said that the universal production of things, whether ab aeterno or not, is neither a motion nor a change. For in order that there be motion or change, it is required that something be other now than previously, and thus there would be something previously existing, and consequently this would not be the universal production of things about which we are now speaking.

975. Similarly, Averroes’ statement that something is said to come to be from its opposite per accidens and from a subject per se is true in particular productions according to which this or that being comes to be, e.g., a man or a dog, but is not true in the universal production of being.

This is clear from what the Philosopher said in Physics I. For he said there that if this animal comes to be inasmuch as it is this animal, it ought not come to be from “non-animal” but from “non-this-animal”—for example, if a man comes to be from non-man or a horse from non-horse. But if animal is produced precisely as animal, it must come to be from non-animal. Accordingly, if some particular being comes to be, it does not come to be from absolute non-being; but if the whole being comes to be, i.e., if being precisely as being comes to be, it must be made from absolute non-being—if, indeed, this process should be called “being made,” for it is an equivocal way of speaking, as has been said.

What Averroes introduces about the early philosophers has no value, for they were unable to arrive at the first cause of all being but considered the causes of particular changes.

The first of these philosophers considered the causes solely of accidental changes, and posited all “being made” to be alteration. Those who succeeded them arrived at a knowledge of substantial changes, but those who came still later, such as Plato and Aristotle, arrived at a knowledge of the principle of all existence.

Consequently, it is clear that we are not moved to assert that something comes to be from nothing because we suppose only visible things to be beings; rather it is because we do not content ourselves with considering merely the particular productions of particular causes, but go on to consider the universal production of all being from the first principle of being. Nor do we assert that to need matter in order to act is due to a diminished power, in the sense of such a power’s lacking its natural energy, rather, what we say is that this is proper to a particular power, which does not extend to all being but makes a particular being.

Hence one can say that it is characteristic of a “diminished power” to make something from something in the sense that we would say that a particular power is less than the universal power.

976. Then at (754), assuming that a mobile and a mover are required in order that there be motion, Aristotle argues in the following manner: If motion has not always existed, it is necessary to say either that mobiles and movers were at some time made, having previously not existed, or are eternal. If, therefore, it is held that each mobile has been made, it is necessary to say that previous to the change which is taken as the first, there was another change and motion according to which was made the very mobile which is able to be moved and to have been moved. This inference, indeed, depends on the preceding. For if it is granted that motion has not always been but that there is some first change before which there was none, it will follow that that first change involved a mobile, and that that mobile was made, for previously it did not exist—since it is being supposed that all mobiles have been made. Now, whatever comes to be after having previously not existed, comes to be through a motion or a change. But the motion or change through which a mobile comes to be, is prior to the change by which the mobile is moved. Therefore, prior to the change which was presumed to be first is another change and so on ad infinitum.

But if it is held that things which are mobile always pre-existed even when no motion existed, this seems to be unreasonable and a sign of ignorance. For it immediately appears that if mobiles exist, motion ought to exist, for natural mobiles are at once also movers, as is clear from Book III. But if natural mobiles and movers are existing, there must be motion.

But to enter more deeply into our search for the truth, it is necessary that this same thing happen—if mobiles and movers are assumed to be eternally existing prior to motion—that followed from the assumption that they were made, namely, that prior to the change supposed to be the first, there is other change ad infinitum. This is evident in the following way: If it be supposed that certain mobiles and certain movers exist, and yet the first mover begins at some time or other to cause motion and something is moved by it, and before this nothing is being moved but is at rest, it will be necessary to say that there was another change in the mover or mobile made prior to that which was assumed to be the first one produced by the mover beginning to cause motion, The truth of this is clear from the following:

Rest is the privation of motion. Privation, however, is not present in a thing capable of habit and form except on account of some cause. Therefore there was a cause—either on the part of the mover or on the part of the mobile—why there was rest. Therefore, as long as that cause prevailed, there was always rest. If, then, a mover begins at some time to cause motion, the cause of rest must be removed. But it cannot be removed except by a motion or change. Therefore, it follows that before that change which was said to be first, there is a prior change by which the cause of rest is removed.

977. Then at (755) he proves the necessity of the foregoing argument. For someone could say that it happens that things are at rest at some time and in motion at some time, without any pre-existing cause of rest to be removed. Hence he wishes to refute this. And about this he does two things:

First he premisses something needed for his proof;

Secondly, he presents the proposed proof, at 978.

He says therefore first that among movers, some move “singularly,” i.e., in just one way, while others move with respect to motions that are contrary. Things that cause motion in just one way are natural things, as fire always heats and never cools. But beings that act through intellect are causes of motions that are contrary, for one and the same knowledge seems to deal with things and their contraries, as medicine is the science of health and of sickness. Hence one sees that a doctor by means of his science can cause motions that are mutually contrary.

Now Aristotle mentioned this distinction among movers, because in things that act through intellect it does not appear that what he had said is true, namely, that if something is moved when previously it had been at rest, the cause of the rest ought first be removed. For things that act according to intellect seem to be ready to move to opposites without any change of themselves being involved; hence it seems that they can cause motion and not cause it, without any change.

Therefore, lest his argument be forestalled by this objection, he adds that his reason holds both for things that act according to intellect and that act by nature. For things that act by nature do always per se move to one, but per accidens they sometimes move to the contrary, and in order that such an accident occur, some change is necessary; thus cold always per se causes coldness, but per accidens it produces warmth.

But that cold should per accidens cause warmth is due to some change affecting the cold object, either inasmuch as it is moved to another location, thus making it differently related to the object which is now made warm by it than it was when it was making it cold, or inasmuch as it completely departs.

For we say that cold is the cause of warmth by departing in the way that a captain is by his absence the cause of the sinking of a ship; again, cold becomes per accidens the cause of warmth either by moving farther away or by approaching closer, as in the winter the interior of animals is warmer, because their heat retreats inward on account of the surrounding cold.

The same applies to things that act by intellect, For knowledge, although it is one thing dealing with contraries, does not deal equally with them both but with one principally, as medicine is per se ordained to causing health. Therefore, if it happens that a doctor uses his knowledge for the contrary purpose of causing sickness, this will not be per se from this science but per accidens, on account of something else. And in order that that something else occur when previously it did not exist, some change is required.

978. Then at (756) he sets forth the proof which manifests his proposition. He says therefore that from the fact that things are such, i.e., that a similar situation prevails with respect to things that act by nature and things that act by intellect, then, speaking universally of all, we can say that whatever things are possible to make, or to be acted upon, or to cause motion, or to be moved, cannot cause motion or be moved in just any disposition in which they find themselves, but according as they are in some definite state and nearness with respect to each other.

And this he concludes from the premisses, because it has already been said that both in things that act according to nature and in things that act according to will, none is the cause of diverse things except as it is a different state. Accordingly, it is necessary that when the mover and the moved approach one another according to a suitable distance and likewise when they are in whatever disposition is required for one to cause motion and for the other to be moved, then the one must be moved and the other must cause motion.

If, therefore, there was not always motion, it is clear that existing things were not in that state that allowed for one to cause motion and another to be moved; rather, they were in the state of not being able to cause motion and of being moved at that time. But later they reached that state in which one moves and the other is moved. Therefore, one or the other of them changed.

For we see that in all things which are said to be “to something” it does not happen that a new relation arises except through a change affecting one or other or both, as, for example, if something which previously was not “double” has now become double, even though not both of the extremes were changed, yet at least one of them was. Accordingly, if there newly arises a relationship by which something causes motion and something is moved, then one or other or both had to be previously moved. Hence, it follows that there is a change prior to the one assumed to be the first.

979. Then at (757) he explains his proposition with an argument from time.

First he premisses two things necessary for his proposition. The first of these is that “prior” and “subsequent” cannot occur unless there is time, since time is nothing else than prior and subsequent precisely as numbered. The second is that time cannot be, unless there is motion. This, too, is clear from the definition—given in Book IV—describing time as the number of motion with respect to prior and subsequent.

980. Secondly, at (758) he concludes to a conditional proposition from statements made in Book IV, For there, according to his doctrine, he stated time to be the number of motion; according to the doctrine of the other philosophers time is a motion, as he there stated. But whichever of these is true, it follows that this conditional is true: If time always exists, it is necessary that motion be perpetual.

981. Thirdly, at (759) he proves in two ways the antecedent of this conditional. First, from the opinions of others. And he says that all the philosophers but one, namely, Plato, seem to be in accord with regard to the opinion that time is not begotten, i.e., that it did not begin to exist after previously not existing. Whence, Democritus also proved that it is impossible that all things should have been made in the sense of newly beginning to be, because it is impossible that time have been so made that it begin newly to be.

Only Plato generates time, i.e., says that time was newly made. For he says that time was made at the same time as the heavenst and he supposed that the heavens were made, i.e., that they have a beginning of their duration, as Aristotle here claims, and as Plato’s words seem at first glance to indicate—although Platonists say that Plato asserted that the heavens were made in the sense that they have an active principle of their existence but not as having a principle of their duration. Thus, therefore, does Plato alone seem to have conceived that time cannot be without motion, for he did not suppose that time existed before the motion of the heavens.

982. Secondly, at (760) he proves the same point by an argument, namely, from the fact that it is impossible to say or to understand time to exist without the “now,” just as it is impossible that there be a line without a point, The “now,” however, is something intermediate, having as part of its nature that it be at once a beginning and an end, i.e,, the beginning of a future time, but the end of a past. From this it appears that it is necessary for time always to be. For whatever time is taken, its boundary is a “now” in both senses. And this is clear from the fact that nothing is actual in time but the Itnow,” because what is past has gone by, and what is future does not yet exist. But the “now” which is taken as the boundary of time, is both a beginning and an end, as has been said. Therefore it is necessary that from both aspects of whatever time is taken, time always be; otherwise the first “now” would not be an end, and the last not a beginning.

But from the fact that time is eternal, he concludes that motion too must be eternal; the reason for this conclusion being that time is a property of motion, for it is its number, as was said.

983- But the argument of Aristotle does not appear efficacious. For the “now” is to time as the point is to the line, as was explained in Book VI. But it is not necessary that a point be an intermediate, for some points are merely the beginnings of lines and others the ends, although every point would be both a beginning and an end if the line were infinite. One could not, therefore, prove that a line is infinite from the fact that every point is a beginning and an end; rather it is the other way around: from the fact of a line’s being infinite, one would go on to prove that every point would be both a beginning and an end. Accordingly, it also appears that the claim that every “now” is a beginning and an end is not true, unless time is assumed to be eternal. Therefore in assuming this as a middle term, i.e., that every “now” is a beginning and an end, Aristotle seems to suppose the eternity of time—the very thing he ought to prove.

Now Averroes, in trying to save Aristotle’s argument, says that the attribute of always being both a beginning and an end belongs to the “now” inasmuch as time is not stationary like a line but flowing. But this does not pertain to the proposition. For from the fact that time is flowing and not stationary, it follows that one “now” cannot be taken twice in the way that one point is taken twice, but the flow of time has nothing to do with the “now” being at once a beginning and an end. For the notion of begining and end is the same in all continua whether they be permanent or flowing, as is clear from Book VI.

984. And therefore another explanation must be furnished in accord with the intention of Aristotle, which is that he wishes to derive the fact that every “now” is a beginning and an end from what he had first supposed, namely, that “prior” and “subsequent” would not be, if time did not exist. For he uses this principle which he supposes for no other purpose, but deduces from it that every “now” is a beginning and an end. For let us suppose that some “now” is the beginning of a time; but it is clear from the definition of a beginning, that the beginning of a time is that before which nothing of the time existed. Therefore, there must be taken something “before” or “prior” to the “now” which is assumed as the beginning of the time. “Prior,” however, does not exist without time. Therefore, the “now” which is taken as the beginning of a time is also the end of a time. In the same way, if a “now” be taken as the end of a time, it too will be a beginning, because an end is by definition that “after which” nothing of a thing exists; but “after” cannot be without time. Therefore, it follows that the “now” which is the end of a time is also a beginning.

985. Then at (761) he shows that motion will always be. And he shows this on the part of motion, because the argument from motion given above concluded only that motion never began, whereas the argument from time concluded both, i.e., that it never began and that it never ceases. He says therefore that the very argument by which it was proved that motion never began can prove that motion is indestructible, i.e., that it will never end. For just as from the assumption that motion began it followed that there was a change prior to the change assumed to be first, so too, if it be supposed that motion at some time ceases, it follows that a change will occur after the one assumed to be the last,

How this follows he explains by abbreviating the more diffuse explanation he gave with regard to the beginning of motion. For he had supposed that if motion began, the mobiles and movers either began or always were. The same alternatives can be taken here, namely, that if motion should cease, the mobiles and movers will remain or they will not. But because he had previously shown that the same conclusion follows from either alternative, here therefore he uses only the one alternative, i.e., the supposition that motion ceases in such a way that the mobiles and movers also pass away.

Therefore, beginning with the assumption mentioned, he says that both the actual motion and the mobile do not pass away simultaneously, but just as the generation of a mobile is prior to its motion, so the ceasing-to-be of a mobile is subsequent to the passing away of its motion. This is so because something combustible can remain after combustion ceases.

And what was said of the mobile must also be said of the mover, because a mover in act does not in ceasing to be cease at the same time to be a mover in potency. Accordingly, it is evident that if even the mobile cease to be after the destruction of its motion, then there has to be a process by which the mobile passes out of existence.

And again, because we are supposing that all mobiles and motions are ceasing to be, it will be necessary later that even the cause of their ceasing-to-be cease to be. But because ceasing-to-be is a type of motion, it will follow that after the final change, other changes occur. But since this is impossible, it follows that motion endures forever.

986. These, therefore, are the arguments by which Aristotle intends to prove that motion always has been and will never cease, The first part of which, i.e., that motion always existed, conflicts with our faith, For our faith admits nothing as eternally existing but God alone, Who is utterly immobile—unless, of courset you wish to refer to the act of the divine intellect as a motion, but that would be an equivocal sense, and Aristotle is not here speaking of motion in that sense but of motion properly so called.

The other part of the conclusion is not entirely contrary to the faith, because, as was said above, Aristotle is not treating of the motion of the heavens in particular but of motion universally. Now we believe according to our faith that the substance of the world indeed began, yet so as never to cease. For we posit that some motions will always exist, especially in men who will always remaing living an unceasing life either of happiness or misery.

But some, vainly trying to show that Aristotle concluded nothing contrary to the faith, have said that Aristotle does not intend here to prove as a truth that motion is eternal but to allege reason for both sides of a question that is doubtful. Rut this is a foolish statement to anyone who investigates Aristotle’s procedure here. Moreover, he uses the eternity of time and of motion as a principle to prove the existence of a first principle both here in Physics VIII and in Metaphysics XII. That shows he considered it proved.

987. But if one rightly considers the arguments here given, the truth of the faith is not assailed by them, For they prove that motion did not begin through the way of nature, as some taught it did, but that it did not begin by things being created by a first principle of things, as our faith holds, cannot be proved by these arguments. And that will be evident to anyone who considers each of the inferences here drawn by Aristotle.

For when he asks whether, if motion did not always exist, the movers and mobiles always existed or not, the reply must be that the first mover always existed; other things—movers or mobiles—did not always exist, but began to exist from the universal cause of all existence. But it has been pointed out above that the production of all being by the first cause of being is not a motion, whether this coming-forth be taken to be ab aeterno or not. Accordingly, it does not follow that before the first change there was a previous change. But this would follow if the movers and mobiles were newly brought into existence by some particular agent acting upon some presupposed subject that would be changed from non-being to being, or from privation to form—and Aristotle’s argument concerns this way of coming into existence.

988. But because we posit that at least a first mover always existed, we need to give an answer to his subsequent deduction that, if movers and mobiles pre-exist, and motion begins newly to be in them, then the movers or mobiles could not have been previously in that disposition in which they are while there is motion, and therefore, some change must have preceded the first change.

Now, if we are speaking of the motion itself, the answer is easy: the mobiles were not previously in that disposition in which they now are, because previously they did not exist; hence they could not be moved. But, as it has been said, they received their existence not through a change or motion but through coming forth from the first principle of things; accordingly, it does not follow that before the first change there was a change. But there still remains the question about the first production of things. For if the first principle, which is God, is no different now than before, then neither does he produce things now any more than before; but if he is different, at least the change affecting him will be prior to the change which is supposed to be the first.

And indeed, if he were a cause that acts only through nature and not through intellect and will, this reason would conclude necessarily. But because he acts through will, he can through an eternal will produce an effect which is non-eternal, just as by his eternal intellect he can understand a thing that is non-eternal—the thing understood being in a certain way the principle of action in causes that act by intellect, as a natural form is in causes that act by nature.

989. But a further point must be pursued. For we do not say that a will postpones doing what it wants, unless something is expected in the future that does not yet exist in the present, as for example, when I will to make a fire not now but later, because in the future it is expected to be cold, on account of which I make the fire; or at least a presence of time is awaited. But that time succeeds time does not occur without motion. Therefore, it cannot be that a will, even if it be immutable, postpones doing what it wills, without some motion being involved, Accordingly, the new production of things cannot come forth from the eternal will except by means of motions succeeding one another ad infinitum.

Now those who raise this objection fail to see that it assumes a thing acting in time, i.e., something that acts on the assumption that time exists; for in this kind of action which occurs in time, one must consider some determinate relationship to this time or to things that exist in this time to explain why it be performed in this time rather than in some other time. But this reasoning has no place in the universal agent, which produces time itself at the same time that it produces other things.

For when we say that things have not always been produced by God, we do not understand that an infinite time preceded, in which God refrained from acting and that later, at a definite time, He began to act; rather, we understand that God produced at once both time and things after they did not exist. Accordingly, we must not consider in the divine will that it willed to make things not then but later, as though time were already existing; rather, we must solely consider the fact that he willed that things and the time of their duration should begin to be after they had no existed at all.

If it be asked why he willed this, it must be said without a doubt that it was for his own sake. For just as he made things because of himself, in order that in them the likeness of his goodness be manifested, so he willed that they not always be, in order to show his self-sufficiency, from the fact that, although nothing else existed, he in himself had all sufficiency of happiness and of power to produce things.

And this can indeed be said as far as human reason can grasp divine things, saving, of course, the secret of divine wisdom which cannot be comprehended by us.

990. Because the solution of this argument proceeded on the supposition that time did not always exist, there remains the problem of solving the argument which seems to prove that time always existed. And perhaps Aristotle, after the argument from motion, gave one from time, because he thought that the one from motion would be inefficacious, unless time was assumed to be eternal. His statement, therefore, that whenever there is time there must be a “now” existing, must be granted without demur. But the statement that every “now” is both a beginning and an end should not be conceded, unless it be also granted that motion always existed, so that every indivisible of motion (which is called a “moment”) should be both a beginning and an end of motion—for the “now” is to the moment as time is to motion. If, therefore, we suppose that motion has not always existed, but that we can take some first indivisible in motion before which nothing of motion existed, we can also take some “now” in time before which there was no time.

Now we have already shown, in explaining the text, that what Averroes says to bolster this argument is inefficacious. But neither is there any efficacy in what Aristotle cites to bolster his own position, namely, that “before” and “after” do not exist without time.

For when we say that a time’s beginning is “that before which nothing of the time existed,” we are not thereby compelled to say that the “now” which is the beginning of the time, is preceded by a time signified by the word “before,” any more than in magnitudes, if I say that the beginning of a magnitude is “that beyond which nothing exists of that magnitude,” it is necessary to say that the phrase, “beyond which beginning,” signifies some real place existing in nature—for it signifies an imaginary one only. Otherwise, it would be necessary to posit a place beyond the universe, whose magnitude is finite and has a beginning and an end.

Similarly, the first “now” which is the beginning of time is not preceded by a time existing in reality but only in our imagination. And this is the time that is described when one says that the first “now” is the beginning of time, “before which” nothing of time exists.

Or it may be said that in the expression, “the beginning of time is that before which nothing of time exists,” the word, “before,” is not affirmed but denied—and so it is not necessary to posit a time before the beginning of time. For in things which exist in time, it happens that some certain time precedes their beginning, as, when it is said that the beginning of youth is that before which there was nothing of youth, the word “before” can be taken in an affirmative sense, because youth is measured by time. But time is not measured by time; hence no time preceded its beginning; hence the word “before” in the definition of time is not taken affirmatively but negatively.

But before time there does exist a duration, namely, the eternity of God. But this eternity has no extension or any before or after as time does; rather, it is all at once—and is not of the same nature as time any more than the divine magnitude is of the same nature as a bodily magnitude.

Therefore, just as when we say that “outside” the universe there is nothing but God, we are not positing some dimension outside the world, so too, when we say that “before” the universe nothing existed, we are not positing any sort of successive duration before the universe.

Lecture 3

Arguments against Anaxagoras and Empedocles

991. After presenting the reasons showing that motion always existed, the Phillosopher here gives arguments against Anaxagoras and Empedocles who posited the contrary. About this he does two things:

First he gives an argument against their position;

Secondly, against the argument they presupposed, at 992.

He says therefore first that since it has been shown that motion always exists, it is wrong to say, as Empedocles and Anaxagoras did, that at some time motion exists and at another time it does not; for to make such a claim is a figment, because it has no basis. Something stated without a reason or the support of divine authority seems, indeed, to be a fiction. However, divine authority has more value than human reason, much more indeed than the authority of a philosopher is more valuable than the weak argument some child might give. Therefore, what is held by faith, even though it be believed without an argument is not a figment of the mind, because we believe on the divine authority approved by miracles —works that God alone can produce.

992. Then at (763) he objects against the argument on which they rested. About this he does three things:

First he suggests that their argument is unsuitable;

Secondly, that it was more unsuitable to Anaxagoras’ position than to that of Empedocles, at 993;

Thirdly, he shows that even according to Empedocles’ opiniont it is unsuitable, at 994.

He says therefore first (763) that it also seems a fiction that anyone, positing that motion at one time exists and at another time does not, should give as his reason that this is so because it is natural for it to be that way, and then adds that this statement must be accepted as a principle. Now that is what Empedocles seems to say, namely, that the situation whereby during one period of time things maintain friendship, and during another are ruled by discord that sets things in motion, but in the interim are at rest, is due to a sort of necessity in things. That is like saying that the reason why heat warms is that it has to be that way, and that heat warms should then be accepted as a principle. This is exactly what Empedocles does, when he takes as a principle that it is due to an ordinance of nature that things are at one time being moved by friendship, and at another time by discord, and at another time are at rest.

Perhaps Anaxagoras, too, and others who posit one active principle would speak in a similar vein, namely, that we must accept as a principle that moti6n began to exist after not existing for an infinite period of time.

993. Then at (764) he shows that Anaxagoras used this argument in a more unsuitable way than did Empedocles. For it is clear that when something is laid down as a principle, it should be accepted as being according to the nature of a thing, i.e., that the nature of a thing is such that such a thing belongs to it. Thus we accept the principle that the whole is greater than its part, because it is the very reason and nature of a whole that it exceed the quantity of a part. Hence, when Empedocles says, “It is natural that it be that way,” he gives us to understand that it should be accepted as a principle. Anaxagoras would have said the same, although he did not express it.

But it is clear that no natural thing nor anything that belongs to things naturally, can exist without ordert because nature is a cause of order. For we see that nature in its works proceeds in an orderly fashion from one thing to another. Therefore, whatever does not possess order is not according to nature and cannot be called a principle.

But two infinites have no order, one to the other, because there is no ratio between one infinite and another, whereas every order is a kind of ratio. Accordingly, it is evidently not a work of nature that things rest for an infinite time and later begin to be moved for an infinite time without there being, between this time and that, any difference to explain why motion comes to be now rather than before; any more than it is a work of nature not to assign some other order between the two thingst so that when one fails the other begins and motion comes to be, as Anaxagoras posited. These are not works of nature, because whatever is in nature either is always the same and not sometimes this way and then that way—as fire always moves upwards—or there is some reason why it is not always the same, as for example, animals do not always continue growing but reach a point when they start to decrease—and for this there is a reason.

Accordingly, it does not seem to be according to nature that for an infinite time things be at rest and later begin to be moved, as Anaxagoras assumed.

Hence it is better to say, as Empedocles said—and those who believed as he—that the whole universe is at rest at one time and in motion at another, because at least in this case there would be order, for there can be a ratio between one finite and another.

It should, however, be considered that the tenet of our faith is not akin to Anaxagoras’ position, for we do not assume before the world any infinite reaches of time that have to be related to a later time; rather, before the world began, only the simple eternity of God existed, and that is outside the genus of time.

994. Then at (765) he shows that the above-mentioned argument is not appropriate in Empedocles’ situation either.

First he explains the proposition;

Secondly, he rejects a false interpretation, at 995.

He says therefore first (765) that even the holder of Empedocles’ theory ought not to assert the fact only but also should explain the cause of his statement and not go beyond what is required by the cause he assigns. Nor should he accept anything as an axiom, i.e., as a principle without reason; rather, whatever is accepted as a principle should be explained either by induction, as is done in the case of natural principles based on sense experience, or by demonstration, as in the case of those principles which are proved by prior principles. But Empedocles does not do that. Granted that he posits friendship and discord as causes, yet it is not the property of friendship or hostility that one should cause motion after the other. For it is not the nature of friendship to be changed into hostility, or vice versa; though it is of the nature of friendship to gather and of hostility to scatter.

But if it is further determined that at one time the one gathers and that at another time the other scatters, it must be further made clear by definite instances in which this occurs. For example, that friendship gathers and discord scatters is manifested among men, because by the former men are united but by the latter they fly from one another. So Empedocles supposed that this is what happens in the whole universe, because it seems to happen in certain cases. But that according to equal periods friendship should move at one time and discord at another, needs to be supported by argument, since that is not seen to happen among men.

995. Then at (766) he rejects a false assumption. For someone could believe that whatever is eternal has no cause, since whatever we observe as being caused among us is something that begins newly to be. Consequently, it seemed to some that when a discussion reached something that always existed, there was no need to inquire any further for a cause or a reasons In this vein Empedocles could say that friendship and discord had always caused motion according to equal times and therefore no reason for it need be sought. But Aristotle disqualifies this by saying that it is a wrong assumption to suppose that we have an adequate first principle in virtue of the fact that something always is so or always happens so. In this way Democritus reduced all the causes that explain nature to something existing always: he assigned a principle for things that begin newly to be, but would not look for a principle of what has always been, Now this is true in some things and not in others. For it is clear that a triangle always has three angles equal to two right angles, but even of this eternal property there is a cause other than the fact. But some things are indeed eternal, such as principles, that do not have a cause.

996. Very special attention should be paid to what is here said, because, as is mentioned in Metaphysics II, the arrangement of things in existence and in truth is the same. Therefore, just as some things are always true and yet have a cause of their truth, so Aristotle understood that there are some eternal beings, namely, the heavenly bodies and separated substances, which nevertheless have a cause of existence.

From this it is evident that although Aristotle posited a world that was eternal, he did not believe that God is not the world’s cause of existence but of its motion only, as some maintained. Finally, he concludes his main proposition with a summary. And he says: “Let this conclude what we have to say in support of our claim that there never was a time when there was not motion and there will never be a time when there will not be motion.”

Lecture 4

Solution of arguments concluding motion was not always

997. After giving arguments proving that motion always exists, the Philoper accidenssopher now intends to answer objections to the contrary. About this he does two things:

First he gives the arguments;

Secondly, he answers them, at 1000.

In regard to the first he gives three arguments, after first stating that it is not difficult to solve the objections contrary to his position. And he says that there are three main arguments from which it seems to follow that motion began to be at some time after previously not existing at all.

The first of these is that whereby he proved in Book VI that no change is infinite, because by the same argument it can be proved that no change is eternal. For no terminated change is eternal any more than it is infinite. But every change is terminated. For every motion is naturally from something to something, and these two are contraries; hence, of necessity, the termini of any change are the contraries within the sphere of that change. But because contrariety of termini is not evident in all cases of local motion, Aristotle adds something common to every motion, namely, that nothing is moved to infinity, because nothing is moved to what it cannot reach, as has been said in Book VI, Accordingly, it is clear that no motion is perpetual, just as it is not infinite. If, therefore, no motion is perpetual, it also seems possible to posit a time in which there is no change. This first argument is taken from motion.

998. The second argument is based on the mobile, at (768). It is this: If motion cannot newly come to be when previously it was not, it seems fitting to say of anything that either it is always in motion or never in notion; because if motion can sometimes be and sometimes not be in one particular mobile, why not for the whole universe? But we see that it is possible for something to be moved that previously was not moved as a whole, and that had no motion in itself with respect to any of its parts, as is apparent in non-living things, among which some mobile begins at one time to be moved when previously no part had been moved, nor the whole itself, but it was completely at rest. It remains, therefore, that in the whole universe there can be motion where previously there was none.

999. But because in non-living things, even though motion is seen to begin anew in something when previously there was none at all, yet motion appears to have been pre-existing in something external by which it is moved, he accordingly gives a third argument from animals, which are moved not from without but by themselves.

This argument is at (769). and it says that it is more evident in animals than in the non-living that motion begins after previously having not existed. For when we have rested for a time so that ho motion exists in us, we begin at a certain time to be moved and the principle of our motion is from our very selves even if nothing external moves us. This, however, does not happen in non-living things, because they are moved always by something external, such as the cause that generates them, or a cause that removes an obstacle, or a cause that subjects them to force. From this it follows, if an animal is at one time entirely at rest, that motion begins to exist in an immobile being after previously not existing in it, which motion does not originate from an external mover but from the very thing that is moved. And if this can occur in an animal, there is nothing to prevent its occuring in the universe. For an animal and especially man possesses a likeness to the world; wherefore it is said that man is a small world. Accordingly, if in this small world, motion can begin after previously not existing in it, it seems that the same can happen in the large world. And if this happens in the world, it can happen in the infinite whole, which some assumed exists beyond the world—provided, of course, that there is something infinite that can rest and be moved.

1000. Then at (770) he answers these arguments in order.

In answer, therefore, to the first he says that it is correct to say that motion which occurs between contraries cannot always endure as one and the same numerical motion, because perhaps this is necessary, as will be proved later—and he leaves this in doubt, because it has not yet been proved. But because someone could say that even motion which is between contraries can be always numerically the same on account of maintaining the same mobile which is repeatedly moved from one contrary to another—for example, if it is first moved from white to black, and then from black to white, and so on throughout time—he then adds that it is not possible that a motion which is always in one and the same mobile be kept one and the same by repetition. And he explains this by an example: Let the same chord be continually struck on a lyre and let the striker be unvarying in his striking; one may ask whether the motion and sound of the one chord struck twice is one and the same or continually other and other.

Yet whatever be the case with other mobiles, there is nothing to prevent a motion which is not between contraries, such as a circular motion, from being the same continual and perpetual motion. This will be made clearer from later development. Therefore, although every motion is finite with respect to its termini, yet by repetition some motion can be continuous and perpetual.

1001. Then at (771) he answers the second argument. And he says that it is nothing unusual for a non-living thing to begin to be moved when previously it was not being moved, provided that this occurs because an external mover is present at one time and not at another. For it is clear that motion must pre-exist on the part of a mover which at some time becomes near but previously was not so. However, this seems to be a point to be looked into as a problem, namely, whether, if a mover exists, the same object can be at one time moved by this mover and at another not—for he had previously said that such a thing cannot happen unless there intervenes some change affecting either the mover or the mobile. Accordingly, motion always pre-exists, whether or not a mover pre-exists. Now this point seems to need investigation, because whoever proposed this argument seems to be certain about everything but one factor, namely, whr it is that things at rest do not always rest, and mobiles are not always in motion.

1002. Then at (772) he answers the third argument, And he says that the third objection causes the greatest problem about whether motion can exist after previously not existing, based on what is seen to happen in living things. For it seems that an animal which previously was at rest, later begins to move about without any external cause of motion; accordingly, it seems that that motion of the animal was not preceded by any motion, either in the animal or in anything else, as happens in non-living things.

But it is false that the motion of the animal does not come to be from something external. For we always observe in animals something naturally moved, whicht namely, is not moved through will. And the cause of its be,ing moved naturally is not the animal through its appetite, but perhaps the cause of this natural change is its surroundings, i.e., the air, and beyond that the heavens, as is plainly the case when the body of an animal is altered by heat or coldness of air.

And he says, “perhaps,” because in an animal something is also moved naturally by an internal principle, as is evident in those changes which occur in the vegetal soul, such as are the digestion of food and the subsequent transmutations, which are called “natural” because they do not follow upon apprehension and appetite. And because this seems to be contrary to what is proper to an animal, which is to move itself, he adds that when we say that an animal “moves itself,” we do not understand this of any and every motion, but of local motion, according to which an animal moves itself through apprehension and appetite.

Accordingly, there is nothing to prevent—indeed, it is necessary—many changes from taking place in the body of au animal on account of its surroundings, i.e., the air and the heavens, some of which changes move the understanding or the appetite, by which in turn the whole animal is moved.

1003. It should be noted that Aristotle here declares the way in which heavenly bodies act upon us. For they do not act directly on our souls but on our bodies; but when our bodies are moved, then per accidens a change occurs in the powers of the soul, which are acts of bodily organs, but not necessarily in the intellect and the intellective appetite, which do not use bodily organs. Yet the intellect and will sometimes follow upon some of these changes, as when a person through his reason chooses either to pursue or to reject or to do something on account of a passion which began in the body or in the sensitive part. And therefore Aristotle does not say that all motions caused by the surroundings move the intellect or appetitet but that some of them do. In this way he excludes necessity from the intellective powers.

Of the things he said he gives an example from sleeping things, in which there seems to be maximum rest with respect to animal motions. But even though during sleep there be no motion that is sensible, i.e., proceeding from sense apprehensiong animals rise awakened by some motion existing within, due either to the work of the nutritive soul, as when, as a result of the food’s being digested, the vapors which caused sleep vanish and the animal is aroused, or when the body is altered by its surroundings, from heat or cold.

Thus it is clear to anyone who considers the matter diligently that no motion ever newly appears in us unless some other motion preceded. And he promises to give a fuller explanation of this later.

Lecture 5

Five ways in which things may be disposed with respect to motion or rest.

Two first excluded.

1004. Having shown in Book VII that there is not an infinite process in movers and in mobiles but that a first must be reached, and having now shown that motion has always been and always will be, the Philosopher goes on further to consider the condition of the first motion and of the first mover. And his treatment is divided into two parts.

In the first he shows that the first motion is eternal and that the first mover is entirely immobile;

Secondly, from this he proceeds to show the condition of the first motion and of the first mover, (L. 14).

The first is divided into three parts:

In the first he gives a division having five members;

In the second he excludes three members of this division, at 1006;

Thirdly, he investigates the two remaining members to see which of them is truer, because the truth of what he intends to settle depends on it, (L. 6).

1005. He says therefore first (773) that the reason for the following consideration, in which we intend to investigate about the first motion and the first mover, is that it pertains to a question he raised in answering the second argument (given in the preceding lecture), namely, that of whence it happens that certain things are at one time in motion and at another time at rest, and are not either always in motion or always at rest since motion in common is considered perpetual.

And he says that the ways in which things are disposed with respect to motion or rest are necessarily limited to three. The first of which is that all things be always at rest and nothing ever in motion; the second is that all things be always in motion and nothing at rest; the third way is that some things are in motion and others at rest.

But the third way is again divided into three ways. The first of these is that some things are in motion and some at rest in the sense that the ones in motion are always in motion and those at rest always at rest, and nothing is at one time in motion and at another time at rest.

The second way is the converse, ioeol that all things are apt to be in motion and to rest and that nothing is either always in motion or always at rest.

The third way is that certain things are always immobile and never in motion; others are always mobile and never at rest; still others may be taken with both, i.e., with motion and rest, so as to be in motion at one time and at rest at another.

This last member must be determined by us to be the truth, because in it are contained the solutions of all objections. And when we shall have shown this, we shall possess the end which we intend in this work, namely, to arrive at a first eternal motion and a first immobile mover.

Therefore, it is in the above manner that the third member of the first division is divided into three members, thus making a general division consisting of five members.

Now, it should be noticed that in three of these members all things are respectively put in one definite disposition; for example, in the first member all things are taken to be always at rest; in the second all things are always in motion; and in the fourth all things alternate between motion and rest. But in one member, namely, the third, beings are divided according to two dispositions, so that some are always in motion and others always at rest. Finally, in one member, the fifth, beings are divided according to three dispositions; namely, some are never in motion, others are never at rest, while the others are sometimes in motion and sometimes not. Notice, too, in this last member that it is not rest but immobility that is posited; because the first mover, who is never moved, can not strictly be said to be at rest, for, as was said in Book V, only what is apt to be moved, and is not being moved, is properly said to be at rest.

1006, Then at (774) he excludes three members of the division.

First he posits that not all things are always at rest;

Secondly, that not all things are always in motion, at 1007;

Thirdly, he excludes the third member, in which it was said that the things in motion are always in motion and those at rest are always at rest, (L. 6).

In regard to the first he posits three statements. The first of these is that it is due to a weakness of understanding that some affirm rest of all things and in support of their stand search for a sophistic reason without referring to sense. For it proceeds on the fact that the intellect is not capable of destroying sophistical arguments which conflict with things evident to sense. But it has been said in Topics I that there is no need to dispute against positions or problems that are in a mind which needs sense or punishment. Hence it is not necessary to dispute this position, due to its stupidity.

The second thing he says is that this problem does not concern a particular being but being in general. Nor does it affect natural science alone, but in a way all demonstrative sciences and all opinions, i.e., all the arts which use opinions, as do rhetoric and dialectics, for all the arts and sciences make use of motion. For the practical arts in a way direct certain motions, and natural philosophy speculates about the nature of motion and about mobile beings. Mathematicians, too, make use of motion, i.ee, of an imagined one, saying that a point in motion makes a line. The metaphysician, however, considers first principles. Accordingly, it is plain that to destroy motion conflicts with all sciences.

Now an error that affects all beings and all sciences is not to be reproved by the philosopher of nature but by the metaphysician. Thereforet it is not the business of natural philosophy to dispute this error.

The third thing he says is that unreasonable and inappropriate problems about the principles of mathematical sciences do not pertain to mathematics to be answered. The same is true in the other sciences. In like manner, it is not the business of the physicist to destroy an affirmation that is contrary to its principles. For in each science the definition of the subject is assumed as a principle; hence in the science which deals with nature, it is assumed as a principle that nature is a principle of motion. Accordingly, in the light of these three statements, it is apparent that it does not belong to natural philosophy to dispute this position.

1007. Then at (775) he excludes the second member, in which Heraclitus posited that all things are always being moved. And first he compares this opinion with the previous one which posited that all things are always at rest; and he says that to say that all things are always in motion, as Heraclitus said, is both false and contrary to the principles of natural science. Yet this position is not in as great conflict with the art as the first one is.

But that it does conflict with the art is clear, because it takes away the assumption of natural science that nature is principle not only of motien but also of rest, which supposition makes it clear that rest is something natural just as motion is. Hence, just as the first opinions which destroyed motion, was against natural science, so too is this one that destroys rest.

The reason why he says that this opinion is less against art is that rest is nothing more than the privation of motion. But it is less evident that there is no motion than that there is no privation of motion. For there are some motions so weak and insignificant that they can be scarcely noticed; for that reason it is easy to suppose that something is at rest when it really is not. But great and strong motions cannot be concealed; hence it cannot be said that the senses are deceived in perceiving motion as they are in perceiving rest.

Therefore, secondly, at (776) he shows how some posited this second opinion. And he says that some, such as Heraclitus and his supporters, have said that all things which exist are always in motion, and not some things only or just at some time, but this motion eludes our senses. Now, if they say this of some motions, they are correct; for some motions do elude us. But because they do not qualify their statement but speak of all motions, it is not hard to find arguments against them, for there are many motions which evidently could not have existed always.

1008. Thirdly, at (777) he forms the arguments against this position.

First with respect to the motion of growth;

Secondly, with respect to the motion of alteration, at 1009;

Thirdly, with respect to local motion, at 1012.

The reason he begins with growth is that Heraclitus was led to his doctrine as a result of considering growth. For he observed that a person grows a small amount in one year and, supposing that growth is continuous, he believed that in each part of that year he was increased with respect to part of that quantity; and yet that increase is not sensed, because it comes in a small portion of time, He reasoned, therefore, that the same thing happens in other things which seem to be at rest.

Against this Aristotle says that it is not possible for a thing to be continually increased or diminished so that the increased quantity can be divided according to time in such a way that in each part of time there is a corresponding increase. Rather, there is, after the increase of one part, a time in which there is no increase but a disposition is produced for the increase of the next part.

And this he explains with kindred examples. The first of these is that we see that the multiplication of drops of rain breaks a stone. The second example is that we see that things being born, i.e., that plants born in stones divide the stones. Now, we cannot say that, if the repeated drops dig out or remove a certain quantity of the stone in a given time, half of this number of drops in half the time would previously remove half of that quantity. But what happens here is what happens with regard to shiphaulars. For it does not follow, if 100 men pull a ship a certain distance in a given time, that fifty of them will move it half the distance in the same time or the full distance in twice the time—this was said in Book VII. So also it does not follow, if many drops cave in a stone, that some part of those drops had previously removed the half in some certain time.

The reason for this is that what is removed from the stone by many drops is indeed divisible into many parts, but none of them is removed separately from the stone, for all the parts are removed at once, in the sense that they are in the totality removed in potency.

And he is speaking here of the first total quantity that is removed, for there is nothing to prevent that, over a long period of time, such a large quantity, be removed from the stone by these drops that a certain part may have been removed previously by a part of these drops. But we must come to a removed quantity which is removed all together and not part after part. Therefore, in the removing of that whole, none of the preceding drops removed anything, but merely disposed for its removal. However, the last acts in virtue of all and removes what the others had disposed to be removed.

The same is true in the motion called decrease. For it is not necessary, if something decreases a certain amount in a given time (even though the quantity be divided ad infinitum), that in every part of that time a corresponding part of the removed quantity should depart; rather, at some time a given amount will depart all together. The same holds in increase. Consequently, it is not required that something be continuously increased or decreased.

1009. Then at (778) he contradicts the above-mentioned position of continuous motion with respect to alteration, and this with three arguments. First, he says that what was said about increase, applies also to alteration. For although a body that is being altered is infinitely divisible, that is no reason for supposing that alteration is divided ad infinitum, so that for each period of time a part of the alteration should occur. Rather, alteration very often takes place swiftly, i.e., many parts of the altered body are altered all at once, as happens when water is condensed or congealed. For a whole mass of water is congealed all at once and not part after part (although if it be a large mass of water, there is nothing to prevent part congealing after part).

It should be noticed that what Aristotle says here about alteration growth seems contrary to what was said in Book VI, where it was shown that motion is divided according to the division of the time, and of the mobile, and of the sphere of motion.

But it should be recognized that in Book VI Aristotle was talking about motion in common, without application to definite mobiles. Therefore, what he discussed there must be taken according to the requirements of motion’s continuity; but at present he is speaking of motion with application to definite mobiles, in which a motion can be interrupted and not be continuous, which, when viewed under the common aspect, could be continuous.

1010. He gives the second argument at (779), and he says that if a sick person is to get well, he has to become healed in a period of time and not in a terminus (an instant?) of the time. And it is further necessary that the very change, which is healing, tend to a definite terminus, ie., to health and not to anything else. Accordingly, every alteration requires a definite time and a definite terminus, because every alteration tends to a contrary, as was said in Book V. But no such change is always continuous. Therefore, to say that something is being always and continuously altered, is to speak against the facts.

1011. The third argument he gives at (780) and he says that a stone does not become harder or softer, even after a very great period of time; thus it is foolish to say that all things are always being altered.

1012. Then at (781) he contradicts the opinion at issue with respect to local motion, on two counts. First, indeed, because some local motions and rests are so evident that they cannot be hidden. For it would be strange if it were hidden from us when a stone is carried downwards or when it is at rest on the earth. Consequently, it cannot be said that, because of the concealment of local motions, all things should be supposed to be always being moved locally.

Tnl3. Secondly, at (782) he argues thus: Earth and any other natural body, when they are in their due placest rest from a necessity of nature and are not removed except by force. But it is evident that certain natural bodies are in their due place. Therefore, it is necessary to say that some things are at rest with respect to place and that not all things are being moved locally.

Finally, he concludes in summary that, from the foregoing and other things similar to the foregoing, anyone can know that it is impossible for all things always to be in motion, as Heraclitus said, or for all things always to be at rest, as Zeno and Parmenides and Melissus said,

Lecture 6

A third member of the division is rejected

1014. Having disposed of two members of the foregoing division, the Philosopher now rejects a third, in which it was posited that things are divided into two dispositions only, in such a way, namely, that some things are always at rest and others always in motion, and there is not a third class of things that are sometimes in motion and sometimes at rest. He rejects this in two ways.

He does this first (783) in the same way that he rejected the two previous positions, namely, on the ground that they are contrary to sense observation. For we see by the senses not only that some things are in motion (which destroys the first position, namelyt of those who posit all things to be always at rest), and that some are at rest (by which is destroyed the second position, of those who maintain that all things are always in motion); but we also see that the aforementioned changes or variations from motion to rest, and from rest to motion, occur in the same things. This shows that there are some things which are sometimes moved and sometimes at rest.

1015. In a second way at (784) he rejects the same opinion on the ground that the one who would engender this doubt would be contrary to what is evident in nature. In the first place it would deny the motion of growth, for we see that growth takes place in things that are not always growing, because, were they always growing, they would be tending not to a definite quantity but to the infinite.

In the second place it would deny compulsory local motion, for a motion is not compulsory, unless something is moved not in keeping with its nature when previously it was naturally at rest; for a forced motion is nothing more than a departure from natural rest. If therefore nothing at rest can be moved, it will follow that what is naturally at rest cannot later be moved by compulsion.

In the third place generation and ceasing-to-be would be excluded by this opinion. For the former is a change from non-being to being, and the latter from being to non-being. Therefore, in order that a thing cease to be, it ought previously to have been existing for a time, and in order that a thing be generated, it ought previously not to have been existing for a time. But whatever is a being or a non-being for some time is at rest (where rest is taken in a very general sense), If, therefore, nothing at rest can be moved, it follows that nothing which is for some time a non-existent can be generated, and that nothing which exists for a time can cease to be.

In the fourth place this position destroys all motion universally, because every motion involves generation and ceasing-to-be either absolutely or in a qualified sense. For what is being moved toward something as toward a terminus is being made such-and-such, so far as alteration and growth are concerned, or being made to be in such-and-such, so far as local motion is concerned; for example, what is being changed from black to white, or from small to large, becomes white or large, but whatever is being moved to a place comes to exist in that place. But from the fact that something is changed from its terminus a quo, a “such and such” ceased to be, when it is a case of alteration and growth, and a “there” ceased to be, if it is a case of local motion. Therefore, because in every motion there is generation and ceasing-to-be, it consequently rejects all motion.

Because such things are impossible, it becomes clear that some things are being moved, but not always; and that some things are at rest, not always, but sometimes.

1016. Then at (785) he studies the other two members of his division.

First he reveals his intention;

Secondly, he pursues it, (L. 7).

About the first he does three things:

First he shows to which opinion the fourth member pertains;

Secondly, he summarizes what has been said in this chaptert at 1017;

Thirdly, he states what remains to be said, at 1020.

He says therefore first (785) that to posit that all things are sometimes at rest and sometimes in motion pertains to the ancient arguments which we touched upon in discussing the eternity of motion. For Empedocles seems to be the chief protagonist of this opinion that all things are at some time moved by friendship and by discord and in the meantime are at rest.

1017. Then at (786) he sums up what has been said in this chapter.

First he recalls the divisions previously made;

Secondly, he recalls the rejection of the first member which posited all things at rest, at 1018;

Thirdly, the rejection of the other two members, at 1019.

He says therefore first (786) that in order to make clearer the intention of what follows, we must begin with what has just been determined and use the same principle as before, namely, that beings must maintain themselves in one of three dispositions, i.e., either that all are at rest or all in motion or some at rest and some in motion. And this third is again divided into three members, for if all things are such that some are at rest and others in motion, then necessarily all must be at one time at rest and at another in motion, or some are always at rest and others always in motion, or to these two a third member may be added, namely, that there are others of which some are at rest not always but sometimes, while the others are in motion sometimes but not always.

l018. Then at (787) he rejects the first member and says that it was said above that it is not possible for all things to be always at rest; but something else must now be added. And he says two things against this position.

First, some motion must be posited at least in the soul. For should anyone want to say that according to truth it is a fact that nothing is being moved (as the followers of Melissus did, who posited that being is infinite and immobile), yet it is also a fact that this does not appear to be so according to sense, for many things appear to the senses to be moving.

If, therefore, anyone declares as false the opinion by which we believe that some things are in motion, it still follows that motion exists. For if there is false opinion, there is motion; and universally if there is opinion, there is motion and, likewise, if there is imagining, there is motion. The reason is that imagining is a motion of the sensitive part and is produced by the sense in act. Opinion also is a certain motion of the reason and proceeds from several acts of reasoning. But it follows even more strongly that there is motion in opinion and imagining, if things appear to be this at one time and that at another. This happens when things at one time seem to us to be at rest and at another time not to rest. Thus, it entirely follows that motion exists.

He says, secondly, against the opinion at issue, that to have the intention of destroying this opiniong and to look for an argument to prove those things that we ought to hold in a respect surpassing the need for proof, since they are accepted as self-evident. To do this, I say, is no different from judging poorly between what is better and what is worse in morals, and between what is credible and incredible in logical matters, and between a principle and a non-principle in matters of demonstration.

For whoever looks for arguments to prove things which are self-evident and, consequently, held as principles, does not recognize them for principles so long as he intends to prove them through other principles. Likewise, it seems that he does not recognize what is credible and what is incredible, because he is trying to prove what is per se credible through something else, as though it were not per se credible. Nor does he seem capable of distinguishing between the better and the worse who tries to prove the more evident by means of the less evident. But it is self-evident that some things are in motion. Therefore, we should not address ourselves to trying to prove this by arguments.

1019. Then at (788) he rejects two more members of his original division. And he says that just as it is impossible for all things to be always at rest, so too is it impossible that all things be always in motion, or that some things are always in motion and some always at rest, so as to leave nothing which is sometimes in motion and sometimes at rest. Against all this, sufficient credence arises from one medium, namely, the fact that we see that some things are sometimes in motion and sometimes at rest. Hence, it is clear that it is impossible to say that all things are continually at rest—which was the first member—and that all things are continually in motion—which was the second member—or that some are always in motion and the remainder always at rest without any mediate possibility.

1020. Then at (789) he shows what is left to be said, and he concludes from the foregoing that since three members of the division cannot stand, what remains is to consider which of the other two is the truer, whether, namely, all things are capable of both motion and rest, or whether some are capable of both motion and rest while still others are always at rest and others always in motion. This last is what we intend to demonstrate. In this way it will be shown that the first motion is eternal, and the first mover immobile.

Lecture 7

Universally, whatever is moved is moved by another

1021. After revealing his aim, the Philosopher now begins to execute it, namely, to establish that not all things are sometimes in motion and sometimes at rest, but that something is entirely immobile, and something always in motion. The treatment is divided into two parts.

In the first he shows that the first mover is immobile;

In the second that the first mobile is always being moved, (L. 13).

The first part is divided into two sections:

In the first he shows the immobility of the first mover from the order of movers and mobiles;

In the second, from the eternity of motion, (L. 13).

The first is divided into two parts:

In the first he shows that the first mover is immobile;

In the second that the first mover is eternal, (L. 12).

About the first he does two things:

First he shows that to prove what follows depends on showing that whatever is moved is moved by another;

Secondly, he shows the proposition, (L. 9).

He had indeed showed above, in the beginning of Book VII, that whatever is moved is moved by another, by a generic argument based on motion itself, but because he has now begun to apply motion to mobile things, he here shows that what was previously proved in a universal way is verified universally in all mobiles and movers. Hence the first part is divided into two parts:

In the first he gives a division of movers and mobiles;

In the second he explains his proposition in individual cases, at 1024.

About the first he does two things:

First he divides movers and mobiles;

Secondly, he explains the division, at 1023.

1022. He gives therefore first (790) three divisions of movers and mobiles. The first of these is that among movers and mobiles some move or are moved per accidens, and some per se. And he takes “per accidens” in a wide sense include what moves or is moved with respect to a part. Hence in explaining what he means by “per accidens, he adds that things cause motion or are moved per accidens in two ways. (1) Whatever things are said to cause motion by virtue of being present in things which move are said to cause it per accidens, as when it is said that a musician causes health, because a knowledge of music is present in the one who heals; and likewise things are said to be moved per accidens either on account of existing in what is being moved in the way that an object in place exists in a place, e.g., when we say that a man is being moved, because the ship on which he is is being moved, or on account of being an accident in a subjects as when we say that the white is being moved, because a body is being moved. (2) In another way, things are said to move or to be moved per accidens, because they move or are moved with respect to a part, as a man is said to strike or be struck, because his hand strikes or is struck.

But when these two per accidens ways of causing motion or being moved are eliminated, things are said to move or to be moved per se, i.e., when they are not said to cause motion or be moved by virtue of being in the cause of motion or in what is being moved, or because some part of them causes motion or is moved.

Therefore, leaving out what causes motion or is moved per accidens, he subdivides things that are moved per se into those which are moved by themselves, as are animals, and those moved by others, as are the non-living.

He gives a third division, namely, that some things are moved according to nature and some not according to nature.

1023. Then at (791) he explains how to discern what is according to nature and what is not according to nature, both in things that are moved by themselves and in things that are moved by something else.

First, with respect to things that are moved by themselves—such as are animals, which move themselves—he says that they are moved according to nature. And he proves this on the ground that they are moved by an intrinsic principle, and since things whose principle of motion is within are said to be moved by nature, it follows that an animal’s motion, by which it moves itself, if it is compared to the whole animal, is natural, because that motion proceeds from the soul which is the nature and form of the animal. But if it be compared to the body, an animal’s motion may be both natural and not according to nature. The difference depends on the type of motion and on the element of which the animal is composed. For if an animal consists of a predominant heavy element, as does the human body, and it is moved upwards, such a movement would be compulsory with respect to the body; but if it is moved downward, it will be a movement that is natural to the body. However, if there were animals whose bodies were composed of air, as Platonists held, then the contrary would be true.

Secondly, he explains how to discern compulsory and natural motions in things that are moved by another. Of these, some, he says, are moved according to nature, as fire upward and earth downward; others are moved outside their nature, as earth upward and fire downward, which is a compulsory motion.

Thirdly, he mentions another type of unnatural motion in animals, namelyt those in which the parts of animals are moved in an unnatural way, their positions and the character of the motion being abnormal. For example, a man’s arms bend (at the elbow) facing forward, while his legs bend (at the knee) facing backward; but dogs and horses and the like, bend the forelegs facing backward and the hind legs facing forward. If motions contrary to these are made, they will be compulsory and not according to nature.

1024. Then at (792) he proves that everything that is moved is moved by another.

First he manifests it in cases that are evident;

Secondly, in cases about which there is doubt, at 1025.

Leaving aside things that are moved per accidens, because such things are not moved but are merely said to be moved when other things are moved, and confining ourselves to those which are moved per se, it is clear, especially in things moved by compulsion and outside their nature, that what is moved is moved by another.

For in the case of things moved by compulsion, it is clear from the very definition of compulsion that they are moved by another. For compulsion, as is said in Ethics III, is that whose principle is from without, with the thing suffering it contributing nothing.

After things that are moved by compulsion, it is clear that what is moved is moved by another if we consider things moved by themselves according to nature, as animals are said to move themselves. For in animals it is clear that something is being moved by something else—but there might yet be a question as to how to distinguish in them the mover and what is being moved. For at first glance it appears to many that what is true with respect to ships and other artifacts which do not exist according to nature, namely, that the part which causes motion is diverse from the part which is moved, applies to animals, for it seems that the soul which causes motion is related to its body which is moved, as the mariner is related to the ship, as is said in On the Soul II. In this way it seems that the whole animal moves itself insofar as one part moves another. But whether the soul is related to the body as a mariner to a ship he leaves to be investigated in his treatise On the Soul. However, the fact that a thing is said to move itself, insofar as one part thereof moves and another is moved, will be shown later.

1025. Then at (793) he explains his proposition in regard to things in which it is more doubtful. About this he does three things.

First he sets down those things in which it is more doubtful that whatever is moved is moved by another, namely, in the heavy and the light, when they are moved according to nature.

Secondly, he shows that they do not move themselves, at 1026;

Thirdly, he shows by what they are moved, (L. 8).

He says therefore first (793) that, since it is in things moved by compulsion, and after them in things which move themselves, that it is especially evident that whatever is being moved is moved by another, the greatest doubt appears to be in the remaining member of the last division, namely, in things that do not move themselves, but yet are moved naturally.

The “last” division to which he refers is that in which he divided things that are moved not by themselves but by another into those that are moved contrary to nature, and those that are moved according to nature. In these latter there is doubt as to what moves them: for example, heavy and light objects are moved to their proper places according to nature—i.e., the light upwards and the heavy downwards—and into contrary places by compulsion; but the source of their motion when they are moved according to nature is not clear, as it is when they are moved contrary to nature.

1026. Then at (794) he proves with four arguments that these things do not move themselves. The first of which is that to move itself pertains to the notion of life and is peculiar to living things; for it is through motions and sensations that we distinguish the animate from the inanimate, as is said in On the Soul I. But it is manifest that the heavy and light as such are not alive, or animate. Therefore, they do not move themselves.

1027. The second argument is given at (795); Things that move themselves can cause themselves to stop, as we see that animals are moved and stop by reason of their appetite, Therefore, if heavy and light things moved themselves with a natural motion, they could cause themselves to stop, in the way that a person who is the cause of his walking is so also of his ceasing to walk. But we see that this is false, because the heavy and the light do not stop outside their proper places, unless some external cause intervenes to halt their motion. Therefore, they do not move themselves.

But because someone could say that although such things are not the cause of their own stopping outside their proper places, yet they are the cause of stopping in their proper places, he adds a third argument at (796): it is unreasonable to say that things which move themselves are so moved according to one motion alone and not by many, because what moves itself does not have its motion determined by another but determines its own motion for itself, so that at one time it determines this motion and at another time that one. Hence it is in the power of what moves itself to determine for itself this or that motion. Therefore, if heavy and light things moved themselves, it would follow that if it were in the power of fire to be moved upward, it would also be in its power to be moved downward, which is something we never see occurring, unless from an extrinsic cause. Therefore, they do not move themselves.

It should be recognized that these two arguments are probable in respect to what appears in things among us that move themselves, which are found at one time to be moved with this motion and at another time with that motion, and at another time to be at rest. Hence he does not say, “It is impossible,” but “It is unreasonable,” which is his manner of speaking when he talks of what is probable. For he will show later that if something is moving itself and it is an entirely immobile mover, that it is always being moved and with one motion. Yet that could not be said in regard to heavy and light things, in which there is nothing that is not moved either per se or per accidens, and they are also generated and cease to be.

1028. He gives the fourth argument at (797): No continuum moves itself. But heavy and light bodies are continua. Therefore neither of these moves itself.

That no continuum moves itself he proves in the following manner: The mover is related to the moved as agent to patient. But since the agent is contrary to the patient, that which is apt to act must be divided from what is apt to be acted upon, Now, to the extent that things are not in mutual contact but are completely one and continuous in quantity and form, to that extent they can not be acted upon by one another, In this way, therefore, it follows that no continuum moves itself, but the mover must be divided from what is moved, as is evident when non-living things are moved by living things, as is a stone by the hand, Hence, too, in animals that move themselves, there is rather a connection of parts than a perfect continuity (for which reason one part can be moved by another), a situation that is not verified in the light and the heavy.

Lecture 8

What moves the heavy and light. Everything moved, moved by another.

1029. After showing that the heavy and the light do not move themselves, he shows.by what they are moved.

First he shows by what they are moved;

Secondly, he concludes to his main intention, at 1036.

About the first he does two things:

First he shows that they are naturally moved by something;

Secondly, he investigates by what they are moved, at 1030.

He says therefore first (798) that although the heavy and the light do not move themselves, they are nevertheless moved by something. And this can be made clear if we distinguish moving causes. For just as in things that are moved, we must take it that (1) some things are moved according to nature and some not, so also in movers, some move not according to nature, e.g., a stick, which is not naturally capable of moving a heavy body such as a stone; and that (2) some things move according to nature, as what is actually hot naturally moves what is according to its nature potentially hot, and similarly in other cases. And just as what is in act causes motion naturally, so what is in potency is naturally moved, with respect either to quantity or quality or where.

And because in Book II he had said that those things are moved naturally whose principle of motion exists in them per se and not by virtue of some concomitant attribute, which might lead one to suppose that what is only potentially hot is, when it becomes hot, not moved naturally in that it is being moved by an external active principle of its motion, he now adds, as though to preclude this objection, “since it has a principle of this kind in itself and not accidentally,” as if to say that in order that a motion be natural, it is enough that a principle of this kind, i.e., the potency, about which he made mention, exist in that which is moved per se and not per accidens, as a bench is potentially combustible, not precisely as bench but as wood.

Hence in explaining the expression “per accidens,” he adds that the same subject can be quantified and qualified, but one of these is related to the other per accidens; what is potentially of such and such a quality is also potentially quantified, but per accidens.

Therefore, because what is in potency is naturally moved by something else in act, and nothing is in potency and in act with respect to the same, it follows that neither fire nor earth nor anything else is moved by itself but by another. Fire and water are moved by another, but by compulsion, when their motion is outside their natural potency; but they are moved naturally when they are moved to their proper acts, to which they are in potency according to their nature.

1030. Then at (799) he shows by what they are moved. And because what is in potency is moved by something in act,

First he distinguishes potency;

Secondly, from this