There remains one last objection to the moral argument for God, which has been made by some theistic philosophers as well as by atheists. The objectors claim that moral truths are necessary truths. This means that they cannot be false, just as a triangle must have only three sides. Moral truths are true in every possible world. A possible world, roughly, is a conceivable or logically coherent and maximal state of affairs. So, in any possible world, either godless or theistic, moral truths obtain, such as “Murder is wrong.” If so, the existence of God is not required to ground moral claims, since there are possible worlds in which no God exists but in which there is objective moral law. Much of what I have argued previously tackles this claim indirectly, since I’ve argued that moral truths cannot just exist as impersonal facts. Such putatative impersonal moral facts are too metaphysically attenuated to serve the functions that morality requires. But it can be added that even if moral truths are necessary truths, this need not dampen or defeat the moral argument for God.
A strong strain of Christian philosophy argues that God’s existence is logically necessarily, as Anselm argued through the ontological argument. That is, God must exist. God exists in all possible worlds and is a logically necessary being. I defended two versions of the ontological argument in chapter ten. If God is logically necessary, then God’s existence in every possible world entails the existence of moral truths in every possible world. So, there is no hindrance to arguing from morality to God, since they are correlative concepts, both occurring in every possible world. Moreover, necessary truths can “stand in relations of explanatory priority to one another.”
The statement “Murder is always wrong” is true in all possible worlds. But it is true in all possible worlds precisely because this statement is a thought in the mind of an omniscient and all-good being. “Murder is wrong” is necessarily true because “God exists” is necessarily true. In the same sense “addition is possible” is necessarily true because “numbers exist” is necessarily true. We cannot have addition without numbers. The conception of the primacy of God in relation to necessary moral truths is found within the Augustinian tradition of understanding moral truths (and all other abstract objects) as necessarily true yet as also dependent on God’s eternal intellection for their existence.