Thanks to the authority vested in them, moral rules are genuine forces, which confront our desires and needs, our appetites of all sorts, when they promise to become immoderate. Clearly, such forces are not material things but if they do not influence the body directly, they do activate the spirit. They contain in themselves everything necessary to bend the will, to contain and constrain it, to incline it in such and such a direction. One can say literally that they are forces. We certainly feel them as such every time we undertake to act contrary to their dictates for they present resistance that we cannot always overcome. When a normally constituted man tries to behave in a way repugnant to morality, he feels something that stops him just as clearly as when he tries to lift a weight too heavy for him. What is the source of this remarkable quality?