The Metaphysics of Morals by Immanuel Kant Chapter 1 Page 21

of the will without regard to the ends which can be attained by the action. For the will stands between its a priori principle, which is formal, and its a posteriori spring, which is material, as between two roads, and as it must be determined by something, it follows that it must be determined by the formal principle of volition when an action is done from duty, in which case every material principle has been withdrawn from it.

The third proposition, which is a consequence of the two preceding, I would express thus: Duty is the necessity of acting from respect for the law. I may have inclination for an object as the effect of my proposed action, but I cannot have respect for it, just for this reason, that it is an effect and not an energy of will. Similarly I cannot have respect for inclination, whether my own or