The 17th century was an extraordinarily fertile period for philosophical speculation concerning the problem of evil, and the writings of Pierre Bayle represent an indispensable point of reference for any historical study of the issue.
Although interest in the question can be seen even in his earliest works, it was the publication of the Dictionnaire historique et critique that gave new impetus to the debate, culminating in Leibniz’s Essais de Théodicée.
In a series of articles that includes Manicheans, Marcionites and Paulicians, Bayle famously argued that the Manichean hypothesis of two independent principles, one purely good and the other purely evil, was better able to account for the existence of moral and physical evil than was any monotheistic theology, including of course Christianity. In the course of his discussion Bayle seeks to demonstrate the inadequacy of traditional responses to the problem of evil, especially that of Augustine, as well as contemporary theories such as Malebranche’s appeal to the simplicity and generality of God’s volitions.
Although Bayle is quite aware of the difficulty posed by the existence of evil for rational theology in general, he is naturally more concerned with attempts to respond to the problem within the framework of orthodox Christian theology.
For Bayle, the most pressing problem is not simply to justify the existence of evil in light of the conception of God afforded by unaided reason. Rather, it is to defend the Christian explanation of physical and moral evil (that is, sin) in a way that is compatible with the theological doctrines of the Fall, predestination, divine grace and the eternal damnation of much of humanity.
As a result Bayle frequently places ad hominem arguments in the mouths of his pagan interlocutors. For example, against King’s claim that the free choice of ends is the source of human happiness and that therefore God’s love of humanity precludes any interference in our free exercise of the will, Bayle points out that "angels and saints" in paradise are determined to love God in such a way that they no longer enjoy freedom of indifference with respect to the choice between good and evil. Yet this loss of freedom in no way diminishes their eternal happiness.
This project consists of a book-length manuscript centered on Bayle’s treatment of the problem of evil. The first half examines Bayle’s criticisms of the principal Christian theodicies, both traditional and contemporary (Malebranche, King) as well as his subsequent responses to the three rationalist critics, Bernard, Jaquelot and LeClerc. The second half turns to Leibniz’s response to Bayle, focusing largely (though not exclusively) on the Theodicy.