The essay examines Kant’s Enlightenment conception of metaphysics as a science (Wissenschaft) to be kept free of ideological prejudice and extrarational cognitive resources and to be established under the conditions of public, intersubjectively valid discourse. I analyze Kant’s self-interpretation of his transcendental philosophy as “metaphysics of metaphysics” and argue for the extensional partial identity of the critique of metaphysics and the metaphysics so rendered possible. In particular, I identify the “future metaphysics” envisioned by Kant as the “metaphysics of nature in general” or the “physiology of pure reason,” which was projected by Kant but never carried out by himself and is not to be confused with the “metaphysics of material nature” presented by Kant in his Metaphysical Principles of Natural Science (1786). I further show how in Kant the “restriction” (Beschr nkung) of the understanding and its pure concepts (categories) to sensible intuition is counterbalanced by the “bounding” (Begrenzung) of sensibility and its formal conditions (space and time) to the appearances, at the exclusion of the “empty space” of the non-sensory. In drawing on Kant’s distinction between “limit” (Schranke) and “boundary” (Grenze), I establish the precise position of critical metaphysics “on the boundary” of the world of sense and the world of the understanding. In concluding, I argue that for Kant a “future metaphysics that will be possible as science” is restricted to transcendental philosophy, at the exclusion of the theoretical cognition of the supersensible, which is thereby delegated forever to the object domain of practically based rational but non-scientific belief or faith (Vernunftglaube).