 The PSR is the subject of Schopenahuer’s 1813 doctoral dissertation: The Fourfold Root of the Principle of Sufficient Reason. In this work, Schopenhauer provides a brief history of the PSR, and then raises the questions of the justification for the PSR and the proper scope of the principle. Schopenhauer follows Wolff in distinguishing among four kinds of reasons, corresponding to four kinds of objects, and charges that much philosophical confusion arises from attempts to explain objects of one kind by reasoning that belongs to the other kind. These four kinds of explanation, or four variants of the PSR, share the very same ground. Along Kantian lines Schopenhauer suggests that it is the subject’s activity in regularly connecting representations that is the ground of the PSR (The Fourfold Root, §16).