One view of the grounds for morality says that good can exist independently of God, and tries to put the burden of proof on the theist to prove that God is necessary for morality. The atheist might say that if we can show that good exists independently of God, then we do not need God to know good, and therefore God is not necessary at all. Hotness is the nature of fire, but hotness can exist outside of fire, therefore fire is not necessary for hotness, or necessary at all.
When we lay this out logically, it would look like this:
1. If goodness can exist in things independent of God, we do not need God for goodness to exist.
2. Goodness can exist in things independent of God.
3. Therefore we do not need God for goodness to exist.
Another way to say it is this:
1a. If we can predicate good independent of God, we do not need God to predicate good.
2a. We can predicate good independent of God.
3a. Therefore we do not need God to predicate good.
The problems with this logic then begin to surface. The first statement is trying to deal with existence, but 2. does not establish existence of anything; it is merely asserted, as in 2a. To prove it would require more than merely thinking of a concept, but would require real examples of good existing independently of God, which may or may not even be possible, let alone provable. Certainly we can predicate goodness in many conceptual situations, but this does not establish existence. While the first statement is attempting to show existence, it is in fact merely predicating concepts, not showing that in fact anything exists.
Further, it seems to be trying to show that because I can conceive of a thing that has the attributes of God but is not God, then I’ve shown that God is irrelevant or does not exist. Just because I can conceive of something that has the attributes of water but is not water, I’ve proven nothing about the existence or non-existence of water.
But each of these have a more fundamental problem. Both 1 and 1a are circular, assuming the conclusion in the premise. The condition (“if we can predicate good independent of God”) contains the conclusion. 1a could be restated ‘If we can predicate good independent of God, we can predicate good independent of God.’ The original question we are trying to answer is whether or not we can have good without God, and stating it in the premises does not prove anything, but assumes the answer from the start.
We still have another problem. Both of these equivocate God’s goodness with goodness we can conceive of in created things. Classical Christian theology, which is where most of these concepts of morality originate in modern times, maintains that there is a fundamental difference between what is contained in God’s nature and what is in the created world. It is true that God is good, and it is true that good exists in the world, but it is not true that the two have the exact same type of good. If God’s goodness was the same as our concept of goodness, then we would fully grasp God’s nature, and all of God would be finite and fallible. Christian theology has always maintained that God is fundamentally different from man, for He is unlimited, unique, and simple (not compound). Thus God is good in an infinite, pure, and unique way.
We only know God’s goodness by analogy. As in any analogy, some of our concept of good is the same as God’s, but some is not. Perhaps the following can illustrate the distinction:
1c. If we can predicate justice independent of God, God’s justice is commonly available in other places without God.
2c. We can predicate justice independent of God.
3c. Therefore God’s justice is commonly available in other places without God.
Here we can change justice for any other attribute of God, such as love, power, knowledge, wisdom, or any of God’s other attributes. God has these things in a way different from us, for His attributes are infinite and undefiled. All human justice is imperfect and fallible, a very different concept than that of God. Just because I see some justice in the world, I cannot conclude I have seen God’s justice.
So the question then arises whether even on an analogous level, the attributes of God can exist or be predicated independent of God. The answer is again no. All of these attributes are known on a scale of perfection: we can distinguish between bad, good, and more good only if we have a standard of perfect good to judge everything by. God is the standard of perfection, and therefore must exist as a measure of all imperfect things. So the best we could do is change God’s perfection into something else and deny it is God, but we cannot get rid of the perfect good by which we measure all other things.
Of course, none of this deals with the fundamental problems of deriving morality from a purely materialistic world, which is all we have if we deny God. For more on this, see here.
In the end, this atheistic attempt to use morality to disprove God fails on several levels.