Scientific explanation is routinely understood to be governed by the principle of methodological naturalism, which excludes putative supernatural causes. This conception of naturalism is dependent on a distinction between natural and supernatural which in modern discussions is regarded as largely unproblematic. However, the natural-supernatural distinction has an important history that shows how interdependent these notions once were. In the past, ideas about the relative self-sufficiency of the natural realm typically relied upon deeper theological or metaphysical assumptions that could not themselves be established by naturalistic methods. In the Middle Ages, when the natural-supernatural distinction first emerged, divine action was an integral component of natural causation. Subsequently, during the scientific revolution, the introduction of the modern conception of laws of nature, understood as divine dictates, collapsed the natural-supernatural distinction, effectively erasing the notion of natural causes. This early modern effacing of any real distinction between natural and supernatural causation paradoxically laid the foundations for a modern science that would later be understood in purely naturalistic terms. Viewed historically, scientific naturalism is indebted to particular notions of divine action.