Gottfried Wilhelm Leibniz

Leibniz is the rare thinker who is canonical in two fields that almost never meet: he co-invented the calculus and he wrote one of the most ambitious modern defenses of the existence of a perfectly good God. Both projects shared a temperament. Leibniz believed the universe was rationally tractable all the way down, and that the reasons for things, if pursued far enough, would always converge on the divine.

He is in this corpus for two reasons. First, his version of the Cosmological Argument from the principle of sufficient reason: the argument that the existence of any contingent thing demands an explanation, that no series of contingent things can explain themselves, and that the explanation must therefore terminate in a Necessary Being. The argument is older than Leibniz, but his statement of it in the Monadology is the cleanest one philosophers still cite.

Second, the Theodicy: his attempt to defend the goodness of God against the Problem of Evil by arguing that the actual world is the best of all possible worlds. Voltaire ridiculed the conclusion in Candide, and the phrase “best of all possible worlds” is now mostly used as a sneer. But the structural move, that defending God against the problem of evil requires reasoning about possible worlds and not just this one, prefigures the entire modern apparatus of the Free Will Defense and Plantinga’s modal arguments.

Leibniz died in Hannover, having outlived his patrons and most of his correspondents, and was buried in a grave that went unmarked for fifty years.