  While Leibniz's Principle of Contradiction and Principle of Sufficient Reason were discussed above, it was not mentioned that these two principles are employed in the service of Leibniz's distinction between truths of reasoning and truths of fact, that is, between necessary truths and contingent truths. Leibniz's account of modality is treated elsewhere, but a short account of this distinction is here required. In the case of a truth of reasoning, its reason or explanation can be discovered by analysis of the notions or concepts, “resolving it into simpler ideas and simpler truths until we reach the primitives” (G VI 612/AG 217). Ultimately, all truths of reasoning will be resolvable into primitives or identities, and the Principle of Contradiction is thereby operative. In the case of a truth of fact, on the other hand, its reason cannot be discovered through a finite process of analysis or resolution of notions. However, there must be a reason that some particular fact is so and not otherwise (PSR), and, according to Leibniz, this reason is found outside the series of contingent things. (See below.)