, the state of rest being privation of motion; then, inasmuch as the two motions that follow the same straight line are contrary motions, and it is impossible for a thing to undergo simultaneously two contrary motions, that which is undergoing locomotion from A to cannot also simultaneously be undergoing locomotion from to A; and since the latter locomotion is not simultaneous with the former but is still to be undergone, before it is undergone there must occur a state of rest at C; for this, as we found, is the state of rest that is the opposite of the motion from.