 His manner of doing so was exceedingly elegant. Kant did not merely challenge the logic of, or poke fun at the extravagances of Leibniz’s metaphysics, though he is not above a joke regarding the monads — potential human lives — he might be swallowing with his morning coffee (2:327). In the antinomies section of the Critique of Pure Reason, he shows that, for every “proof” of an important metaphysical proposition, such as determinism, atomism, or the eternity of the universe, a proof of the contrary proposition, such as the existence of exceptions to mechanical causality, infinite divisibility, or the temporal finitude of the world can be supplied. By attempting to prove too much, human rationality accomplished too little. Traditional metaphysics left reason perturbed, confused, and unfulfilled.