On the Force of Percussion

JOH. AL. BORELLI

the machine is distinguished from the patient by reason only, not by substance, and the same substance is simultaneously in potency and act in these motions; wherefore it is false that all things which move in nature are impelled by a distinct and separate motor.

The physical cause efficient of motion in natural bodies must be corporeal.

Regarding the other part, whether the principle and the immediate physical and natural cause of motion is entirely incorporeal, lacking all magnitude and extension, it seems entirely impossible. For if motion is an action, and that indeed cannot be done without physical contact, it seems entirely incomprehensible that that which is entirely indivisible and not a quantity could apply itself and touch, comprehend, and impel a body that is a quantity, which is what is to be moved. From this it is deduced that a physical mover, which ought to exert an immediate and real physical action onto a body having extension, cannot lack dimensions, and therefore must be something corporeal, so that it may, by immediately touching, promote bodies through physical action.

The same principle efficient of physical motion must also be affected by motion.

Finally, in the last place, it is doubted whether the cause and moving principle ought also to be affected by motion, or if it ought to be entirely at rest. It is known among the followers of Plato that this seems impossible, not to mention incomprehensible, since if two bodies—the mover and that which is to be moved—mutually touch each other, and the mover remains entirely at rest, no one will grasp how the remainder is impelled by it unless the mover, by some effort, agitates itself and moves the remainder from its place. And therefore, that motive virtue constituted in rest would be as if sleeping or dead, and could never imprint motion into the remaining body. And truly, no natural and physical action can be conceived without local motion, unless one wishes to call upon moral motion i.e., metaphorical or non-physical influence (such as that which is attributed by Aristotle to the movers of the heavens, which move as an object of desire and love), which surely cannot exert physical action and motion.