William Lane Craig writes:
*…the doctrine of divine simplicity is one that has no biblical support at all and, in my opinion, has no good philosophical arguments in its favor. Moreover, it faces very formidable objections. So … I do reject the traditional doctrine that God is absolutely simple.
It makes four identity claims:
i. God is not distinct from His nature.
ii. God’s properties are not distinct from one another.
iii. God’s nature is not distinct from His existence.
iv. God has no properties distinct from His nature.
Claim (i) is not unique to God. Angels, too, are identical with their natures. So this claim is not problematic when understood in the medieval metaphysical framework.
Claim (ii) remains problematic, however. Existence is part of God’s nature. But existence is not the same property as, say, omnipotence, for plenty of things have existence but not omnipotence. It remains very obscure, therefore, how God’s nature or essence can be simple and all His properties identical.
Claim (iii) is misrepresented by Wolterstorff, I believe. His is what Thomistic scholars call an “essentialist” reading of Thomas Aquinas’ doctrine: Existence is a property that is included in the divine essence. But many Thomists insist that the correct reading of Thomas is an “existentialist” one: existence is not a property at all, but is the act of being which instantiates an essence. Everything other than God is composed of an essence to which an act of being is conjoined to make it exist as a concrete particular thing. But in a sense, God has no essence on this view, rather He just is the pure act of being unconstrained by any essence. He is, as Thomas says, the pure act of being subsisting. The problem is, this doctrine is just unintelligible.
Finally, claim (iv) runs into the severe problem that God does seem to have accidental properties in addition to His essential ones. For example, in the actual world, He knows, loves, and wills certain things which He would not know, will, or love had He decided to create a different universe or no universe at all. On the doctrine of divine simplicity God is absolutely similar in all possible worlds; but then it becomes inexplicable why those worlds vary if in every one God knows, loves, and wills the same things.
This is not to say that the doctrine of divine simplicity is wholly bereft of value. On the contrary, I have elsewhere defended the view that God’s cognition is simple. But I do think that the full-blown doctrine in all its glory is philosophically and theologically unacceptable.
I invite the Thomistically inclined among us to answer Dr. Craig’s objections.