  Leibniz asserts in the Monadology §§31–32, “Our reasonings are based on two great principles, that of contradiction… [and] that of sufficient reason” (G II 612/AG 217). To these two great principles could be added four more: the Principle of the Best, the Predicate-in-Notion Principle, the Principle of the Identity of Indiscernibles, and the Principle of Continuity. The relation among these principles is more complicated than one might expect. Leibniz sometimes suggests that the Principle of the Best and the Predicate-in-Notion Principle can be said to ground his “two great principles”; at other times, however, all four principles seem to work together in a system of circular implication. And while the Principle of the Identity of Indiscernibles is often presented in contemporary discussions in analytic metaphysics as a stand-alone axiom, Leibniz tells us that it follows from the two great principles. Finally, the Principle or Law of Continuity is actually a principle that Leibniz takes from his work in mathematics and applies to the infinite hierarchy of monads in the world and to the quality of their perceptions; it appears to derive only tenuous support from the Principle of Sufficient Reason.