In this essay I address two puzzles of interpretation posed by Kant’s reply to Eberhard’s charge that there is nothing true in the Critique of Pure Reason that is not anticipated by Leibniz. The first puzzle is whether Kant takes Leibniz to be an idealist. I argue that Kant does not because by “idealism” he means a philosophy that denies the existence of substances other than minds or spirits. By this criterion the mature Leibniz is not an idealist. The second puzzle is more challenging. If Kant seriously regards his Critical philosophy as “the true apology for Leibniz,” then why does he fail to cite their agreement in holding that space and time are ideal? I argue that the solution to this puzzle lies in Kant’s distinction between understanding and sensibility. In Kant’s eyes Leibniz’s theory of space and time is flawed by his failure to see that they are forms of sensibility, not systems of intellectual relations. Kant is reluctant to acknowledge any kinship with Leibniz’s theory that would divert attention away from this supposedly fundamental mistake.