 The scholastics held that because God is the creative cause of all natural beings, he must possess the ideas corresponding to each of his creatures. But because God is eternal and is not subject to change, the ideas must be eternally present in him, although creatures exist for only a finite period of time. This doctrine of course raised many difficulties, which each author addressed with varying degrees of success. One difficulty had to do with reconciling the multiplicity of ideas with God’s unity: since there are many species of being, there must be a corresponding number of ideas; but God is one and, hence, cannot contain any multiplicity. Another, directly related, difficulty had to do with the ontological status of ideas: do ideas have any reality apart from God? If one denied them any kind of reality, it was hard to see how they could function as exemplar causes of things; but to assign too much reality to them was to run the risk of introducing multiplicity in God and undermining the ex nihilo character of creation. 