The concept of freedom alone allows us to find the unconditioned and intelligible for the conditioned and sensible without going outside ourselves. For, it is our reason itself which by means of the supreme and unconditional practical law cognizes itself and the being that is conscious of this law ( our own person ) as belonging to the pure world of understanding and even determines the way in which, as such, it can be active. In this way, it can be understood why in the entire faculty of reason only the practical can provide us with the means for going beyond the sensible world and provide cognitions of a supersensible order and connection, which, however, just because of this can be extended only so far as is directly necessary for pure practical purposes.

Every step one takes with pure reason, even in the practical field where one does not take subtle speculations into considerations, nevertheless fits with all the moments of the Critique of theoretical reason as closely, and indeed of itself, as if each step had been thought out with deliberate foresight merely to provide this confirmation.

Immanuel Kant – Critique of Practical Reason –
Translated by Mary Gregor