This incontrovertible fact maybe confirmed _à priori_ by reflecting that the active principle, or the substantial form, of a primitive element, is not exposed to the influence of any natural agent capable of impairing it. Everything that is impaired is impaired by its contrary. Now, the active principle has no contrary. The only thing which might be imagined to be contrary to a motive power would be a motive power of an opposite nature, such as the repulsive against the attractive. Motive powers, however, do not act on one another, but on their matter only, as matter alone is passive. On the other hand, even if one power could act on another, its motive action would only produce an accidental determination to local movement, which determination surely would not alter in the least the substance of a primitive being. Hence, although two opposite actions, when terminated to the same subject, can neutralize each other, yet two opposite motive powers can never exercise any influence on each other by their natural actions; and therefore, in spite of their finite entity, they are never impaired or weakened, and are applicable to the production of an unlimited number of actions. _A fifth objection._—An action of infinite intensity cannot but proceed from a power of infinite intensity. But, according to the Newtonian law, two elements, when their distance has become infinitely small, act on one another with an intensity infinitely great. Therefore, if the Newtonian law hold good even to the very centre of the element, the elementary power possesses infinite intensity.