The uniqueness of a being by substance is, William argues, a consequence of its absolute simplicity, since nothing could differentiate two or more absolutely simple beings. The absolute simplicity of a being by substance, in turn, is a consequence of the fact that it cannot be caused (not, at least by an external causation; William argues that the being by substance is the Christian Trinity of persons and he admits a kind of internal causation in the Trinity). For everything that is caused is ot