Full Idea
It is impossible to conceive anything at all in the world, or even out of it, which can be taken as good without qualification, except a good will.
Gist of Idea
The only purely good thing is a good will
Source
Immanuel Kant (Groundwork of the Metaphysic of Morals [1785], 393.1)
Book Reference
Kant,Immanuel: 'The Moral Law (Groundwork of Morals)', ed/tr. Paton,H.J. [Hutchinson 1948], p.59
A Reaction
This is precisely the thought of Epictetus, that the will is the source of goodness, because morality resides in choices (as opposed to character, or states of affairs).
Related Idea
Idea 23328 The essences of good and evil are in dispositions to choose [Epictetus]