The Metaphysics of Morals by Immanuel Kant Chapter 2 Page 22

and this accordingly always indicates a want. The dependence of a contingently determinable will on principles of reason is called an interest. This therefore, is found only in the case of a dependent will which does not always of itself conform to reason; in the Divine will we cannot conceive any interest. But the human will can also take an interest in a thing without therefore acting from interest. The former signifies the practical interest in the action, the latter the pathological in the object of the action.

The former indicates only dependence of the will on principles of reason in themselves; the second, dependence on principles of reason for the sake of inclination, reason supplying only the practical rules how the requirement of the inclination may be satisfied. In the first case the action interests me; in the