 The Thomasian-Pietistic School. Under this heading falls a group of philosophers that perhaps should not be called a school, but nevertheless arise from two common sources, namely the writings of Christian Thomasius and also often from Pietism, and generally share one common opponent, namely Christian Wolff. In terms of his influence on Kant, the most important of these is undoubtedly Christian August Crusius (1715–1775). Although Kant is never an uncritical follower of Crusius, it is clear that Kant studied his works intensely from the late 1750s until the middle of the 1760s, often taking his side against that of Leibniz and Wolff. Like others in this group, Crusius argues that the Principle of Non-Contradiction is an empty principle and thus is insufficient for founding metaphysics, that human actions are radically free and so not subject to the Principle of Sufficient Reason, and that moral laws can only be known through the revelation of the divine will (in scripture or in conscience). Nearly all of these disagreements with Wolff stem from the contention that his system is inconsistent with the real significance of such religious concepts as the duty and obedience to God, guilt, and conscience.