How should philosophy be sub-divided? Kant has answered this question in two ways. On the one hand, he recognised the enduring validity of the threefold division of philosophy proposed by the Stoics. On the other hand, he left numerous commentaries regarding the development to which this division is susceptible. But Kant never offered his thoughts on this matter in a systematic and complete form, and his fragmentary teachings on the subject are not always unambiguous. My aim in this paper is twofold: first, to reconstruct the complete division of philosophy which Kant seems to defend, through a systematic ordering of the new criteria for classification which Kant’s idealism introduces into the traditional tripartition of philosophy; second, to indicate the new philosophical disciplines which arise from these criteria.