 In the second Critique, Kant compares the book’s structure with the first Critique and comments: “such comparisons [are] gratifying; for they rightly occasion the expectation of being able some day to attain insight into the unity of the whole rational faculty (theoretical as well as practical) and to derive everything from one principle—the undeniable need of human reason, which finds complete satisfaction only in a complete systematic unity of its cognitions” (5:91). Kant’s tone is confident, but the fact is that “insight into the unity of the whole rational faculty” has once more been postponed. (Prauss 1981 argues that Kant failed to achieve this insight, in part because he did not appreciate how cognitive success is a fundamentally practical goal. Förster 1992 discusses Kant’s reflections on this topic in his final manuscript, the Opus Postumum.)