On the metaphysics side our capacities for knowing point to reason in its theoretical aspect; the a priori foundations of mathematics, physics and transcendent metaphysics. We have the pure forms of intuition (space and time) that structure our experience, and the Ideas (God, world, self).
On the morality side, our capacities for knowing point to reason in its practical aspect; the a priori foundations of morality. Morality, like mathematics, physics, is constituted in part by a priori elements originating in the nature of reason itself. Kant intends to establish the supreme principle of morality; he wants to find a criterion of moral value that is non relative. According to that principle ('the categorical imperative') we have to act in such a way that we treat humanity, whether in our own person or in any other person, always at the same time as an end, and never merely as a means. This moral law arises from reason; I am the author of it, and every one of us in regard to it is autonomous. The moral law expresses my inmost nature as a rational creature.

Tags: Kant