But the beginning of the consideration will be that which was the beginning of the doubt already mentioned, viz. why some things are at one time moved and at another again at rest. It is necessary, therefore, either that all things should always be at rest; or that all things should always be moved; or that some things should be moved, and others be at rest. And again, of these it is necessary, either that those things which are moved should always be moved, and those things which are at rest always be at rest; or that all things should be naturally adapted to be similarly moved, and be at rest; or that which remains, and which is the third thing, is necessary; for it happens that some things are always immoveable, that some are always moved, and that others participate of both these, which is what we assert to be the case: for this contains a solution of all the doubts, and is the end to us of this treatise. To assert, therefore, that all things are at rest, and to investigate the reason of this, laying aside sense, is a certain infirmity of the dianoetic power. The doubt likewise is about a certain whole, and not about a part. Nor is it only adverse to the natural philosopher, but likewise to all the sciences, as I may say, and to all opinions, because all of them use motion.
Again, as the objection about principles, for instance, in mathematical discussions, are of no consequence to the mathematician, and in a similar manner also in other things; so neither is the objection about what is now said, of any consequence to the natural philosopher; for the hypothesis with him is, that nature is a principle of motion. To assert, however, that all things are moved is nearly false indeed, but is less foreign from this method: for in physics it is supposed that nature is a principle, as of motion, so likewise of rest: at the same time, however, motion is a natural thing. Some also assert that it is not true that some things are moved, and others not, but that all things are moved, and always; but that this is concealed from our sense. To these, however, though they do not define what the motion is of which they speak, or whether they speak of allmotions, it is not difficult to reply: for things can neither be increased, nor diminished continually; but there is also a medium. This assertion, however, is similar to that in which it is said that stones are worn away by a drop of water, and are divided by plants germinating from them; for it does not follow that if a drop of water rubs off, or carries away a certain portion of the stone, it, prior to this, rubbed off or carried away the half of such a portion in half the time; but as in drawing a ship along, in like manner so many drops move so much of the stone. A part of them, however, does not move so much in any time. Hence, that which is taken away, is divided indeed into many parts, but no one of them is moved separately, but they are all moved together. It is evident, therefore, that it is not necessary that something should always depart, because the diminution may be divided to infinity, but the whole will some time or other depart. The like also takes place in any kind whatever of alliation: for it does not follow, that if that which can be changed in quality may be infinitely divided, on this account, alliation also may be divided to infinity; but it is frequently produced collectively, as in the instance of concretion.
Farther still, when any one has been ill, it is necessary that there should have been a time when he recovered his health, and that lie should not have been changed in the end of the time. It is also necessary that he should have been changed into health, and not into any thing else; so that to assert that a thing is continually changed in quality, is to doubt about things which are very apparent; for alliation is into that which is contrary. And a stone neither becomes harder nor softer with respect to lation, it is admirable if a stone is latent which is carried downwards, or which remains on the earth. Again, earth, and each of the other elements necessarily remain in their proper places, and are moved from these by violence. If, therefore, some of these are in their proper places, it is necessary that neither should all things be locally moved. That it is impossible therefore, either that all things should be always moved, or that all things should be always at rest, may be believed from these and other arguments of a similar kind. Neither, likewise, is it possible that some things should always be at rest, but others always be moved; and that nothing should at one time be at rest, and at another time be moved. But it must be said that this is impossible, as well in things which have been before mentioned, as in these; for we see that the mutations, already enumerated, take place in the same things. Besides, he who doubts of this opposes the phaenomena; for there will neither no increase, nor violent motion, unless that which was before at rest is moved contrary to nature. This assertion, therefore, subverts generation and corruption. To be moved likewise, nearly appears to all men to be nothing else than for something to be generated and corrupted: for it becomes that, or in that, into which it is changed; but not that from which it is changed, or from whence it is corrupted. Hence it is evident, that some things are moved, and others are sometimes at rest. But to think fit to assert that all things are sometimes moved and sometimes at rest, this must be conjoined to the reasons above adduced.
We must, however, again begin from the things now defined, and from which also we begun before; for either all things are at rest, or all things are moved; or some things are at rest, but others are moved. And if some things are at rest, but others are moved, it is necessary, either that all things should sometimes be at rest, and sometimes be moved; or that some things should always be at rest, and others always be moved; or that some things should sometimes be at rest, and sometimes be moved. That it is not possible, therefore, that all things can be at rest, has been said before, and we shall also now assert; for if it were in reality so as some say, viz. that being is infinite and immoveable, yet this is not apparent to sense, but many beings are moved. If, therefore, there is false opinion, or in short, opinion, there is also motion. This is also the case if there is imagination, though at one time it may appear to subsist in this manner, and at another differently: for imagination and opinion appear to be certain motions. To consider, however, about these things, and to investigate a reason in things in which we are better affected than to require a reason, is nothing else than to judge badly of the better and the worse, of that which is credible, and of that which is not credible; and of principle, and that which is not a principle. In a similar manner, it is impossible that all things should be moved; or that some things should always be moved, and others always be at rest; for one credible argument is sufficient against all these; since we see some things at one time in motion, and at another at rest. Hence it is evident; that it is similarly impossible for all things to be at rest, and for all things to be moved continually, as it is for some things to be always moved, and others to be always at rest. It remains, therefore, to consider, whether all things are of such a kind as to be moved and to be at rest, or whether some things subsist in this manner, but some are always at rest, and some are always moved: for this must be shown by us.
