Abstract

Leibniz denies Spinoza’s claim that all possible things actually exist. He also denies necessitarianism, Spinoza’s claim that all truths are necessary truths. Both denials seem plausible. What is surprising, however, is Leibniz’s view that the first claim entails the second, i.e., that the existence of all possible things implies necessitarianism. Why think this? Couldn’t it be that, as a matter of contingent fact, all possible things actually exist? There seems to be no incoherency in claiming both that all possible things actually exist and that fewer things could have existed. In this paper, I explain why Leibniz thought that such a position is indeed inconsistent. My thesis is that the Principle of Sufficient Reason plays a decisive role in his reasoning. Leibniz claims that the non-existence of a thing requires a sufficient reason. He also holds that if all possible things can coexist, such a reason cannot be given. Together these claims rule out a scenario in which all possible things actually exist, but only contingently so.