 Clarke sided with Locke and Newton against Descartes in denying that we have knowledge of the essence of substances, even though we can be sure that there are at least two kinds of substances (mental and material) because their properties (thinking and divisibility) are incompatible. He defended natural religion against the naturalist view that nature constitutes a self-sufficient system and defended revealed religion against deism. Clarke adopted Newton’s natural philosophy early on. Through his association with Newton, Clarke was the de facto spokesperson for Newtonianism in the first half the eighteenth century, not only explaining the natural science but also providing a metaphysical support and theological interpretation for it.