It may, however, be doubted why permanencies and motions are in the mutation according to place, both according to, and contrary to nature, but are not in other mutations. Thus, with respect to change in quality, one kind is according to, and another contrary to nature: for a tendency to health is not more according to or contrary to nature, than a tendency to disease; nor a tendency to whiteness than a tendency to blackness. The like also takes place in increase and diminution; for neither are these contrary to each other, as if by nature, or contrary to nature; nor increase to increase. And there is the same reasoning with respect to generation and corruption: for neither is generation according to nature; but corruption contrary to nature; since to grow old is according to nature. Nor do we see that generation is partly: recording, and partly contrary to nature. If, however, that which is by violence, is contrary to nature, the corruption which is violent will be contrary to that which is not violent, in the same manner as that which is contrary to that which is according to nature. There are, therefore, certain generations which are violent and not fatal, to which those that are according to nature are contrary: and there are violent augmentations and diminutions, to which those according to nature are contrary; such as the augmentations of those who, through luxury swiftly arrive at puberty; and corn, which rapidly becomes ripe, and without constipation. But how does this take place in change according to quality? Shall we say, after the same manner? For some of the changes will be violent, and others natural. Thus, some are liberated from disease, not in critical days, and others in critical days; of whom, the former are changed in quality contrary to, and the latter according to, nature. But corruptions will be contrary to each other, and not to generation alone. And what should hinder? For this takes place in a certain respect; viz. if the one is pleasant, and the other painful. So that corruption is not simply contrary to corruption; but so far as one of them is of this kind, and the other of that. In short, therefore, motions and rests arc contrary in the manner we have mentioned; as, for instance, the upward to the downward; for these are contrarieties of place. But fire is naturally borne along by that lation which tends upward; and earth by that which tends downward: and these lations are contrary. But fire is carried upward naturally, and downward unnaturally: and its natural motion is contrary to that which is unnatural. And permanencies in a similar manner: for permanency above, is contrary to the motion from above to below. This permanency, however, would be to the earth contrary to nature, and that motion would be to it according to nature. So that permanency is contrary to motion; viz. the permanency which is contrary to nature, to the motion which is according to nature of the same thing, for the motion of the same thing is thus contrary; for one of them will be according to nature, which is upward or downward; but the other contrary to nature. There is, however, a doubt, whether there is a generation of all rest which has not a perpetual subsistence, and whether this is to stand still. Of the rest, therefore, which abides contrary to nature, as of the rest of earth when on high, there will be a generation. Hence earth, when it is violently driven on high, will stand still. But that which is capable of standing still always appears to be borne along swifter; but, on the contrary, that which is moved by violence. Hence, not having been made quiescent, it will be quiescent. Again, to stand still seems to be properly asserted of that which is naturally borne along to its own place; i.e. it either seems to be wholly this, or at least it at the same time happens to be so. But there is a doubt, whether the permanency which is here, is contrary to the motion which is here: for when a thing is moved from this, or abandons rest, it still appears to possess that which is abandoned. So that if this rest is contrary to the motion which is from hence to the contrary, contraries; will be at the same time inherent. Or will it, in a certain respect, be at rest, or will it still abide? And, in short, that which is in motion, is partly here, and partly in that into which it changes. Hence, motion is more than rest contrary to motion. And thus, concerning motion and rest, we have shown how each is one, and what those motious and rests are, which are contrary to each other. Someone however may doubt concerning standing still, whether any rest is opposed to such motions as are contrary to nature. It is absurd, therefore, if there will not be; for it abides, but by violence. So that there will be something at rest, which is not always at rest without the generation of rest. But it is evident that there will be: for as some thing may be moved contrary to nature, so also it may be at rest contrary to nature. Since, however, to some things there is a motion according to, and contrary to nature; as to fire, a motion upward is according to nature; but downward, contrary to naturc, whether is this contrary, or the motion of earth? For this is borne downwards according to nature. Or is it not evident that both these motions are contrary, yet not after the same manner; but the one as that which is according to nature, to that which is according to nature. But the upward to the downward motion of fire, is as a motion according, to a motion contrary to nature. The like also must be said respecting pcrmanencies. And thus concernmg motion and rest we have shown how each is one, and what those motions and rests are which are contrary to each other.
