  While Leibniz’s view that every substance has a complete concept reinforces the centrality of reason in his epistemology, in doing so, it seems to undercut human and even divine volition, and thereby to slide toward Spinozism. If every fact about Julius Caesar, and indeed, every other fact about the universe is rationally deducible from the Roman Dictator’s complete concept, then it would seem that only one course for the universe is possible. However, this is not a step that Leibniz was willing to take. Were there no distinction between contingent and necessary truths, argued Leibniz, fatalism would be true, and human liberty of the will would be impossible. Leibniz sought to avert this result by distinguishing between hypothetical and absolute necessity. Absolute necessity, he argued, is governed by the principle of contradiction. Something is absolutely necessary if its negation is logically impossible. Hypothetical necessity, on the other hand, describes a state of affairs that is necessary ex hypothesi—that is, just in case a particular antecedent holds—but not logically necessary. On Leibniz’s account, the fact that Caesar crossed the Rubicon is only hypothetically necessary; it follows necessarily from the existence of the individual substance that is Caesar, but its denial is not logically impossible. According to Leibniz, God at creation conceived of an infinite array of possible worlds. The myriad contingent facts of each of these worlds are only hypothetically necessary. That is, they would only be necessary if God were to instantiate that world. Since the present world is the one that God chose to instantiate, all of the contingent facts of this world are certain. However, they are nonetheless contingent since their negation implies no absurdity. That is, there was no logical impossibility preventing Caesar from deciding not to cross the Rubicon. In this sense, his will—and, indeed, human will generally—is free.  Leibniz’s argument for hypothetical necessity has an obvious antecedent in Descartes’s doctrine of created truth. However, unlike Descartes, Leibniz limited the doctrine’s scope to contingent truths. He nonetheless hoped to avoid Spinozist necessitarianism. Whether or not he succeeded in doing so is a matter of debate in the literature.