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.
According to him, all truths rest upon two great principles: the Principle of Contradiction (which says that a truth is necessary just in case its negation is a contradiction) and the PSR.
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.
With this general background on our two great principles in place, together with how these principles operate in Wolff (sometimes in contrast with how they operate in Leibniz), we now turn to a consideration of how these principles operate in Du Châtelet's opening chapter of the Foundations.
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.
