The Metaphysics of Morals by Immanuel Kant Chapter 1 Page 12

In order to do this, we will take the notion of duty, which includes that of a good will, although implying certain subjective restrictions and hindrances. These, however, far from concealing it, or rendering it unrecognizable, rather bring it out by contrast and make it shine forth so much the brighter.

I omit here all actions which are already recognized as inconsistent with duty, although they may be useful for this or that purpose, for with these the question whether they are done from duty cannot arise at all, since they even conflict with it. I also set aside those actions which really conform to duty, but to which men have no direct inclination, performing them because they are impelled thereto by some other inclination. For in this case we can readily distinguish whether the action which agrees with duty is done from duty, or from a selfish view.