If there is one God, why are there so many religions? Might all be false? Some revert to a relativism that allows different 'truth's' for different people, but this is incoherent. This Element argues that monotheism has provided the basis for a belief in objective truth. Human understanding is fallible and partial, but without the idea of one God, there is no foundation for a belief in one reality or a common human nature. The shadow of monotheism lies over our understanding of science, and of morality.