The body of a projectile is moved by a virtue transmitted and propagated by the throwing subject.

It is obvious that projectiles are carried by an actual and true movement after being separated from the throwing subject. Such a movement, since it is some action or operation, must be necessarily produced by some cause, but not by nothing. This cause cannot be the action of the throwing subject while throwing and carrying the mobile, if this mobile is assumed to have left and to be separated from the throwing subject. Consequently, the projectile must be moved forwards by some vicarious motive force provided by the throwing subject itself or at least by some other external impeller such as the air or the water in which the projectile travels, since no other cause than these can seemingly be thought of. But it was shown above that a projectile is not moved by propulsion by the ambient fluid. The body of the projectile thus is necessarily moved by a virtue transmitted and propagated by the throwing subject.

The same point demonstrated by another argument.