In his magnum opus, the "Historical and Critical Dictionary", Pierre Bayle offered a series of brilliant criticisms of the major philosophical and theological systems of the 17th Century. Although officially skeptical concerning the attempt to provide a definitive account of the truths of metaphysics, there is reason to see Bayle as a reluctant skeptic. In particular, Ryan contends that Bayle harbored deep sympathy for the attempt by Descartes and his most innovative successor, Nicolas Malebranche, to establish a metaphysical system that would provide a foundation for the new mechanistic natural philosophy while helping to secure the fundamental tenets of rational theology. Through a careful analysis of Bayle's critical engagement with such philosophers as Spinoza, Leibniz, Locke and Newton, it is argued that, despite his reputation as a skeptic, Bayle was not without philosophical commitments of his own. Drawing on the full range of Bayle's writings, from his early philosophical lectures to his final controversial writings, Ryan offers detailed studies of Bayle's treatment of such pivotal issues as mind-body dualism, causation and God's relation to the world.