This essay considers Kant’s concept of the highest good from a systematic point of view. The two spheres of freedom and nature—of the practical and theoretical—need to be brought into a causal relation for the highest good to be achieved. Kant seems to offer numerous possibilities for how human beings are able to think that it is possible for the highest good to be attainable. I argue that it is only in the third Critique, however, that Kant articulates an answer (...) that also establishes freedom and nature within a larger system. The third Critique does this by positing a third, independent and mediating sphere of human experience that allows a transition between freedom and nature to be effected. This answer to the problem of the highest good is distinctive because the causal efficacy of reason in attaining its own demands is preserved. I examine Kant’s view by way of an analysis of his discussion of ‘territory’ and ‘domain’ in the Introduction to the text. (shrink)