 Baumgarten follows Wolff in distinguishing between two possible forms of idealism, first egoism, which admits the existence of only one spirit, that of the person contemplating such a doctrine, and then idealism proper, which allows the existence of multiple spirits. But both are refuted by the same argument. This argument builds on a Leibnizian principle not hitherto mentioned, the principle of plenitude, or the principle that the perfection of the most perfect world, which is the one that God created, consists in the maximal variety of the universe compatible with its unity or coherence (e.g., “Monadology”, §58, PPL: 648), which was in turn the basis of one of Leibniz’s arguments for the identity of indiscernibles. Baumgarten then argues simply that a universe that contains not only more substances but also more kinds of substances rather than fewer is a more perfect universe, and necessarily exists in preference to the other; and a universe that contains not only multiple minds rather than a single mind but also bodies in addition to minds is therefore a more perfect universe than either of the former would be, and is therefore the kind of world that actually exists. In his words,