 In line with this conception, Kant proposes three questions that answer “all the interest of my reason”: “What can I know?” “What must I do?” and “What may I hope?” (A805/B833). We have seen his answer to the first question: I can know this world as revealed through the senses, but I cannot know the total sum of all that exists, nor a world beyond this one (a supersensible world). Kant does not answer the second question until the Groundwork of the Metaphysics of Morals, four years later. (Arguably, he sees no need to answer the question in this form, since he is confident that people have long known what their duties consist  in.[13])  But the first Critique does include some observations on hope—that is, faith in God and a future world. We certainly fall into error if we think reason can know a world beyond the senses. Indeed, Kant insists that such knowledge would corrupt practical reasoning, by imposing an external incentive for moral action—fear of eternal punishment and hope of heavenly reward, what he will later call “heteronomy.” Nonetheless, human reason still has an inescapable interest in belief in God, immortality and freedom. Kant develops this claim more systematically in the second Critique, as discussed below (§2.3).