  Like most of his great contemporaries (Descartes, Spinoza, Malebranche), Leibniz developed a number of arguments for the existence of God. Two of these are presented in condensed versions in the Monadology §§36–45, as a priori and a posteriori arguments (or ontological and cosmological arguments, to borrow Kant's terminology). But they have long histories in Leibniz's thought. Yet, unlike Descartes and Spinoza at least, Leibniz also expended great efforts in explaining and justifying God's justice and benevolence in this world. In other words, Leibniz was keen to answer the problem of evil. His work on this subject led to his thesis, so roundly mocked in Voltaire's Candide, that we live in the best of all possible worlds.