The Metaphysics of Morals by Immanuel Kant Chapter 1 Page 11

nothing, without nature thereby failing of her purpose. For reason recognizes the establishment of a good will as its highest practical destination, and in attaining this purpose is capable only of a satisfaction of its own proper kind, namely that from the attainment of an end, which end again is determined by reason only, notwithstanding that this may involve many a disappointment to the ends of inclination.

We have then to develop the notion of a will which deserves to be highly esteemed for itself and is good without a view to anything further, a notion which exists already in the sound natural understanding, requiring rather to be cleared up than to be taught, and which in estimating the value of our actions always takes the first place and constitutes the condition of all the rest.