 Christian Wolff (1679–1754), the most influential German philosopher of the first half of the eighteenth century, was a follower of Leibniz and developed the latter’s system. Like Leibniz, Wolff assigned to the PSR a central role in his system while attempting to avoid necessitarianism (or “fatalism”). Like Spinoza and Leibniz, Wolff demanded a reason for both the possibility of things [ratio essendi] (i.e., coherence of essence) and for the actualization, or coming to be, of essences [ratio fiendi]. Wolff mildly criticized Leibniz’s grounding of the PSR merely in experience and attempted to marshal several proofs for the principle (Rational Thoughts on God, the World, and the Soul of Human Beings, §§30–31, 143; Ontologia, §§56–78). One of these proofs attempts to prove the PSR relying on the principle of the Identity of Indiscernibles (Rational Thoughts on God, the World, and the Soul of Human Beings §31), while the most famous proof attempts to derive the PSR from the Law of Non-Contradiction. According to the latter, if a thing \(A\) is assumed to exist without reason, than “nothing is posited that explains why \(A\) exists”. This, according to Wolff, would mean that \(A\) exists because of nothing (Ontologia, §70), which Wolff claims to be absurd. Kant criticized the proof claiming that it is based on an equivocal use of the term “nothing” (AK 1:398).