 Widely and rightly regarded as the most sophisticated philosopher within the Thomasian-Pietist tradition, Crusius sets out to offer an alternative to the core claims of the Leibnizian-Wolffian philosophy on topics in metaphysics, epistemology, logic and practical philosophy. As Lange had previously, Crusius targets the principle of sufficient reason, and its employment in Leibnizian-Wolffian metaphysics, for criticism. Crusius diagnoses a number of ambiguities in the Wolffian presentation of the principle. He opts to refer to a reason (ratio; Grund) that, when present, determines something to come to be such that the opposite would be impossible as a determining reason, and accordingly refers to the principle (in the sense intended by Leibniz and Wolff) as the principle of determining reason (Crusius 1743: §II–III). Crusius then critically discusses each of Wolff’s attempts to prove the principle—concerning the first such proof (presented in  §3.1,  above), Crusius claims that the most charitable reconstruction of it is circular. To show this, Crusius reformulates Wolff’s proof as the following syllogism (using Wolff’s preferred terminology):