Compendium of All Natural Science

...traverse space, like those things that change in place; or change in quantity, like those things that are increased and diminished; or in quality, like those things that become hot, warm, and cold; or acquire something of this sort. Since, indeed, all motion is continuous, and those things which are continuous have infinite parts in potentiality, motion also will have attained an infinity of parts. Wherefore those things which are said to be moved have both been moved and will be moved further. For it is very appropriately said that before every motion there has both been motion and there will be. For since those things which are acquired by motion cannot be obtained in an indivisible moment, for that reason it is necessary that whatever is thought to be moved has both been moved before and must be moved thereafter. Furthermore, that motion which is said to have existed before every motion is to be called prior for this reason: that it is seen to have ceased sooner. But the motion which is believed to be future after every motion is called posterior because it is to begin later. Moreover, those motions are of the same genus and species whose ends and boundaries are contained within the same genus or species. However, for a motion to be one and the same, it is necessary that the thing which is moved be one, and that the time in which it is moved, as well as the * mobile thing itself, be continuous. On the contrary, for a motion to be contrary or diverse, it will be necessary for some of those things which were required by us above to be lacking. Those motions which are curved and those which are straight will also be seen as diverse. There are

That the genus according to which it moves be one, * one [thing].