On the Force of Percussion

JOH. AL. BORELLI De causis, & principiis motus.

CHAPTER II.

It is truly a wonder that the efficient cause of so evident a thing, which is always exposed to our senses—such as motion—should be so hidden and unknown. For first, it is ignored whether the effective principle of motion is something corporeal or entirely incorporeal. Likewise, it is debated whether the first physical mover ought to be entirely immobile and resting, or rather if it creates motion in other bodies by means of its own agitation. Finally, it is debated with great contention whether some bodies can be moved by themselves, or rather if whatever is moved must be propelled by a distinct and separate motor. And truly, to start from the latter, it is most evident that some bodies are impelled by a distinct and external motor; thus, all those things which are carried, struck, or projected are most manifestly promoted by an external impeller. But whether all other things that move in the world are likewise propelled by an extrinsic principle and cause, this truly seems impossible and incredible, since heavy bodies and animals seem to move by themselves—that is, from an intrinsic cause and principle. And although there are not wanting those who say they are moved by an external generator, the insufficiency of this evasion is manifest, since when the generator does not exist, is extinct, and does not actually touch and impel the heavy object, who will ever understand it to propel the heavy object by physical action? To say later that a generative motive virtue is left in the heavy body by the generator, by whose help it subsequently performs the motion of descent, is the same as denying that heavy bodies are impelled by an external cause, because the generated or left-behind motive force, which is intrinsically joined to the heavy body itself, is without a doubt what immediately impels the heavy object downward by itself and by physical action. In animals, moreover, it is clear that the first mover is either the spirit or some other animastic vital or soul-derived force, which is an internal cause, not an external and separate one, which moves itself and the organs of the animal. Nor are those things which are commonly brought forward an obstacle—namely, that agent and patient, builder and built, potency and act would not be distinguished if the mover and the moved were the same. To all these objections...

Heavy objects and animals move by themselves and from themselves.