But that is immoveable, which is entirely incapable of being moved, just as sound is invisible; and also that which is scarcely moved in a long time, or which begins to be moved slowly, and which is called difficult-to-be-moved. That likewise is immoveable, which is naturally adapted and able to be moved, but is not then moved when it is naturally adapted, and where, and as it is naturally adapted; which alone among things immoveable, I denominate to be at rest: for rest is contrary to motion; so that it will be a privation of that motion of which it is capable. What motion therefore is, and also rest, how many mutations there are, and what kind of mutations are motions, is evident from what has been said.
