Baron von Philosophy Leibniz's philosophy is a consistent rationalism. The universe forms one context in which each occurrence can be seen in relation to every other. Leibniz's assertion, however, does not imply an unqualified optimism, since evil is a necessary ingredient in even the best of all possible worlds. The ultimate constituents of the universe, in his view, are monads or simple substances, each of which represents the universe from a different point of view. Being simple, monads are immaterial and thus cannot act.
Apparent interaction is explained in terms of the principle of preestablished harmony.
The principle of continuity as expressed in the phrase nature makes no leaps is another part of Leibniz's rationalism. The monads are arranged in an infinitely ascending scale, based on the distinctness with which each represents the universe. A basic distinction in Leibniz's logic is that made between truths of reason, or necessary propositions, whose principle is the law of noncontradiction, and truths of fact, or contingent propositions, based on the principle of sufficient reason. The principle has its root in the divine intellect, and its most important expression is his law of causality. With the decline of interest in metaphysics in contemporary philosophy, recent studies have tended to emphasize Leibniz's significance in mathematics and logic.