In theoretic philosophy Wolff first treats of Logic purified from scholastic interpretations or deductions; it is the logic of the understanding which he has systematized. The second stage is Metaphysics, which contains four parts: first there is Ontology, the treatment of abstract and quite general philosophic categories, such as Being (ὄν) and its being the One and Good; in this abstract metaphysic there further comes accident, substance, cause and effect, the phenomenon, &c. Next in order is Cosmology, a general doctrine of body, the doctrine of the world; here we have abstract metaphysical propositions respecting the world, that there is no chance, no leaps or bounds in nature—the law of continuity. Wolff excludes natural science and natural history. The third part of the metaphysic is rational psychology or pneumatology, the philosophy of the soul, which deals with the simplicity, immortality, immateriality of the soul. Finally, the fourth is natural theology, which sets forth the proofs of the existence of God.[277] Wolff also inserts (chap. iii.) an empirical psychology. Practical philosophy he divides into the Rights of Nature, Morality, the Rights of Nations or Politics, and Economics. The whole is propounded in geometric forms such as definitions, axioms, theorems, scholia, corollaries, &c. In mathematics the understanding is in its proper place, for the triangle must remain the triangle. Wolff on the one hand started upon a large range of investigation, and one quite indefinite in character, and on the other, held to a strictly methodical manner with regard to propositions and their proofs. The method is really similar to that of Spinoza, only it is more wooden and lifeless than his. Wolff applied the same methods to every sort of content—even to that which is altogether empirical, such as his so-called applied mathematics, into which he introduces many useful arts, bringing the most ordinary reflections and directions into the geometric form. In many cases this undoubtedly gives his work a most pedantic aspect, especially when the content directly justifies itself to our conception without this form at all. For Wolff proceeds by first laying down certain definitions, which really rest upon our ordinary conceptions, since these he translated into the empty form of determinations of the understanding. Hence the definitions are merely nominal definitions, and we know whether they are correct only by seeing whether they correspond to conceptions which are referred to their simple thoughts. The syllogism is the form of real importance in this mode of reasoning, and with Wolff it often attains to its extreme of rigidity and formalism.