HKB
a will determined by that law), namely, as the supreme principle of the summum bonum in an intelligible world, by means of moral legislation in it invested with sovereign power.
Is our knowledge, however, actually extended in this way by pure practical reason, and is that immanent in practical reason which for the speculative was only transcendent? Certainly, but only in a practical point of view. For we do not thereby take knowledge of the nature of our souls, nor of the intelligible world, nor of the Supreme Being, with respect to what they are in themselves, but we have merely combined the conceptions of them in the practical concept of the summum bonum as the object of our will, and this altogether a priori, but only by means of the moral law, and merely in reference to it, in respect of the object which it commands. But how freedom is possible, and how we are to conceive this kind of causality theoretically and positively, is not thereby discovered; but only that there is such a causality is postulated by the moral law and in its behoof. It is the same with the remaining ideas, the possibility of which no human intelligence will ever fathom, but the truth of which, on the other hand, no sophistry will ever wrest from the conviction even of the commonest man.
{BOOK2|CHAPTER2 ^paragraph 65}
VII. How is it possible to conceive an Extension of Pure
Reason in a Practical point of view, without its
Knowledge as Speculative being enlarged at
the same time?
{BOOK2|CHAPTER2 ^paragraph 70}