  Maimonides’ answer to the second argument (GP 2.18) is that in a perfect being, willing something new need not imply change. If I will today to take a trip tomorrow and events intercede to spoil my plans, I may have to change my mind, but to suppose that something analogous happens to God is absurd. Assume I will today to do something tomorrow independent of external circumstances — to think about the numerical characteristics of pi. And assume that when tomorrow comes, I do exactly as planned. While I would be undertaking something new, to the degree that I had intended to do it all along, it would be misleading to say that I underwent a change. Certainly I did not undergo a change of mind.