Focusing on Wolff’s Cosmologia generalis , this chapter examines the tension in Wolff’s understanding of the relationship between a priori and a posteriori knowledge. Leduc contends that Wolff adopts two complementary methods to demonstrate cosmological principles, namely, the synthetic method of composition and the analytic method of discovering or inventing. The synthetic method, prioritized in the Discursus praeliminaris, is based on abstract ontological truths and the principle of sufficient reason and results in a scientific cosmology that demonstrates the properties of matter and laws of motion. The analytic method, conversely, results in an experimental cosmology that explains the properties of matter and laws of motion by relying on both reason and experience. Leduc explains that the analytic method is elaborated mainly in Wolff’s German Metaphysics, while Wolff’s Cosmologia generalis or Latin Cosmology favors the synthetic approach. He thus argues that despite Wolff’s claims that his doctrines must be grounded on experimental physics, his later cosmological position gives pride of place to the a priori foundation and the abstract way of demonstration. Wolff’s general cosmology is thus representative of an important difficulty in his methodology.