Cosmological and ontological

Nancey Murphy summarizes Kant’s argument that the cosmological argument reduces to the ontological in this way: “Suppose we can argue to the necessary existence of some x by showing that its existence is a necessary condition for the existence of all that we know to exist. How, then, to identify this x with the highest reality, namely God? Only by means of a concept that characterizes God as the one and only necessary (necessarily existing) being. But if we can make this step we could just as well have begun with the concept of God as necessarily existing, as does Descartes’ ontological argument.”