D. To the Fourth Argument

428. To the fourth principal argument [nn.305-306], about the cause of succession in motion, I say that, although there can be contention and dispute about Averroes’ intention and about what he contradicts Avempace in (the way it appears in Physics 4 com.71, ‘On the Vacuum’), yet I say briefly that the cause of succession in any motion is the resistance of the movable to the mover; not indeed such that the mover cannot overcome the movable (for then it would not move it), nor indeed such that the movable is inclined back toward the opposite (for then precisely it is in violent motion) - but resistance such that the movable is always under something to which the term intended by the mover cannot immediately succeed. And this resistance of the movable to the mover is because of a defect in the virtue of the mover and thereby because of the resistance of the medium to the mover and the movable, and by the ‘medium’ can be understood all that necessarily precedes the introduction of the term to be introduced. But such a medium is not necessarily a medium save to a limited virtue; for if there were an infinite virtue, it could put the movable at once in the term ‘to which’ - such that neither because of the opposed form in the term ‘from which’ (the form that the movable would already have), nor because of the mediums naturally ordered between the form that the movable has and the term ‘to which’, would there be a necessity that such a mover should move through such mediums before it introduced the term.

429. The possibility, then, of succession comes from the resistance of the movable to the mover, which is from the resistance of the medium to the movable and the mover, such that this is one resistance. For the movable, insofar as it has a form of the sort that between it and the term such mediums are of a nature to exist, can be continuously moved through the mediums to the term - and by these mediums, which resist the movable so that it cannot at once be in the term, can be understood the divisibility of the parts of the movable, or the divisibility of the parts of the form according to which there is motion, or both these two together. However the necessity of succession is never from this resistance, but is precisely by comparing this resistance to the agent, which the movable resists because of the resistance of the medium to the agent - such that, just as the possibility was from the resistance alone of the medium to the movable, so the limited virtue cannot take away this resistance; and therefore this resistance resists the agent so that it does not at once introduce the term.

430. Then to the arguments introduced for the opposite [n.306], namely that ‘there is no resistance of an angel to himself’ - I say that, as an angel does not act from the infinity of active virtue when he is in heaven, between which ‘where’ and his own ‘where’ on earth many mediums are of a nature to exist, which are also mediums for his own motive virtue - so neither can his own motive virtue make all those mediums and the term, nor even can he at once make the term save by first making those mediums; and for this reason there is here the whole resistance that is required for succession in motion.

431. And when argument is made about the saying of Averroes, about a heavy object, that ‘if it were put in a vacuum it would descend immediately because of a defect of resistance on the part of the medium’ [n.306] - I say that if a vacuum is posited then the heavy object would not move (according to the Philosopher, Physics 4.8.214b12-215a24), because a vacuum cannot give way to a heavy object and because separate dimensions cannot be together. However, if it were posited that a vacuum could give way and that there was space in it, and not that the sides of the plenum were together (because then there would not be a vacuum) - I say then that there would be motion successively of the heavy object in the vacuum, because a prior part of the vacuum would be prior and also because the whole heavy object would pass through this part of space before that part; and, as was said before in the second argument [n.350], per se succession is only in local motion and in space insofar as space is a quantum.

432. To the arguments of Aristotle as far as they are adduced for the issue at hand [nn.307-308]:

I say that the proposition ‘what the proportion of medium to medium is in rareness and density, so the proportion of motion to motion is in quickness and slowness’ is true (ceteris paribus), and so it follows that there is no motion in a vacuum - or at least this is true against those [sc. the ancient atomists, Democritus and Leucippus] who posited the vacuum to be the whole cause of motion or of succession in motion; but as to the issue at hand, by arguing similarly here about movables as there about spaces, this proposition ‘what the proportion of movable to movable is in rareness, so the proportion of motion to motion is in quickness’ can be denied. And if you take the proposition ‘what the proportion is of this movable under the idea by which it is movable and of that movable under the idea by which it is movable’, I concede it but then the minor is false [sc. that ‘there is no proportion of angel to body in rareness’, n.307]; for an angel is capable of moving continuously insofar as he has a virtual quantity according to which he can coexist in an extended place, just as a body can, according to its quantity, stand in an extended place.

433. Likewise, as to what the Philosopher infers from his second reason, that ‘motion is in an equal time through a vacuum and a plenum’ [n.308] - if something similar to this is inferred, namely that angel and body would be moved in an equal time, it is not impossible; but there is an impossibility there from the idea of mediums, according to which this sort of reason seems to proceed.

434. But although Aristotle’s reasons would not prove much to the purpose (because movables here are not disposed as spaces are there), yet his reasons are simply valid, such that his major is probative and the other argument leads to an impossibility [sc. the major of the reason in n.307 is probative and is allowed to be true in n.432, and the second reason in n.308 leads to an impossibility by reason of the mediums, n.433].

435. I reply, therefore, that if a vacuum could yield and motion were possible in it, then I say that from the divisibility of the space the motion would have divisibility and succession, just as now from the divisibility of the space of a plenum motion would have per se an essential succession; but over and above this succession can be superadded speed or slowness, by reason of the accidental condition of the medium itself (insofar as it promotes or impedes the motion), or by reason of its rareness (whereby it promotes or at least does not impede motion), or by reason of its opposed density. So in that case there would be motion in a vacuum, and proportionality to the motion in a plenum, and this when speaking of essential succession, but not of the superadded speed or slowness, because a movable in a vacuum would altogether have no superadded speed or slowness

(but it would have some in a plenum, but there is no proportion between ‘nothing’ and something).

436. Therefore Aristotle [n.307] has precisely from this fact [n.435] - against the adversary who says there is motion in a vacuum [n.432] - that there can in a vacuum be no motion having any speed or slowness superadded to essential succession. And this would not be unacceptable if one posited precisely that there was motion in a vacuum -but it would be unacceptable if along with this one were to posit a vacuum as a promotive medium in motion (or a necessary medium in motion), on whose part speed or slowness of motion could be taken.

437. In the same way, what is inferred in the second reason [n.308] is not impossible for an adversary who says precisely that there is motion in a vacuum, because a medium that is a plenum can be equated with a medium that is a vacuum insofar as there is reason or cause for essential succession in the motion; and if some plenum were taken in the sort of proportion to a given motion that Aristotle takes it in, it would be altogether neutral (bestowing no accidental quality), being neither a plenum medium nor a vacuum medium.

438. What then does the Philosopher get against the adversary from this reason [n.308]? - I say that he gets only that a vacuum has no accidental quality over and above essential succession; because if it did, some equal medium could be given and then through the plenum medium and the vacuum medium there would be a motion in as much time as corresponds to the accidental condition of the motion, which is impossible - because if so the mediums would be proportional.