1. THE PROBLEM: HOW CAN PRACTICAL REASON OVERREACH THEORETICAL REASON?

In the Critique of Pure Reason, Kant time and again puts us on notice that various substantive (nonanalytic) truths to which reason can attain on its own, a priori and independently of the empirical deliverances of the senses, are the product of the modus operandi of our specifically human intelligence and are grounded in the specific workings of our human faculty of knowledge. How other intelligences might think in such matters - minds not endowed with our particular modes of sensibility or our particular categories of understanding - is something of which we do and can know nothing. Accordingly, all of our a priori theoretical knowledge is legitimated through, but also confined to, the operation of our human intellect - and is thus restricted in validity to the sphere of how matters stand from a specifically human point of view. In the theoretical domain, man's a priori knowledge is man correlative.

However, when we turn to the practical sphere of the Critique of Practical Reason, matters take on a very different appearance. For Kant here tells us with great explicitness that

Kant is emphatic in insisting that no explicit reference need be made to man as such in dealing with the legitimacy of the principles of morally practical reason, since what matters here is rationality in general rather than humanity in specific: