For Voltaire (and many other eighteenth-century Newtonians) the most important project was defending empirical science as an alternative to traditional natural philosophy. This involved sharing in Hume’s critique of abstract rationalist systems, but it also involved the very different project of defending empirical induction and experimental reasoning as the new epistemology appropriate for a modern Enlightened philosophy. In particular, Voltaire fought vigorously against the rationalist epistemology that critics used to challenge Newtonian reasoning. His famous conclusion in Candide, for example, that optimism was a philosophical chimera produced when dialectical reason remains detached from brute empirical facts owed a great debt to his Newtonian convictions. His alternative offered in the same text of a life devoted to simple tasks with clear, tangible, and most importantly useful ends was also derived from the utilitarian discourse that Newtonians also used to justify their science. Voltaire’s campaign on behalf of smallpox inoculation, which began with his letter on the topic in the Lettres philosophiques, was similarly grounded in an appeal to the facts of the case as an antidote to the fears generated by logical deductions from seemingly sound axiomatic principles. All of Voltaire’s public campaigns, in fact, deployed empirical fact as the ultimate solvent for irrational prejudice and blind adherence to preexisting understandings. In this respect, his philosophy as manifest in each was deeply indebted to the epistemological convictions he gleaned from Newtonianism.