Theists often offer the moral argument in support of God’s existence.  While the argument can take many forms, the essence of the argument is that objective moral values exist, and are best explained by the existence of a transcendent, personal being whose very nature is good.  The common response offered by atheists is that one need not believe in God to be moral and loving.  “After all,” they say, “I am a moral person and I don’t believe in God.  Surely, then, belief in God is not necessary for morality.”

There are two things amiss about this response.  First, it misconstrues the theist’s argument.  He is not arguing that one must believe in God to recognize moral truths (a claim about moral epistemology) or to behave morally, but rather that God must exist for there to even be such a thing as morality (a claim about moral ontology).  God’s existence is necessary to ground moral values in objective reality.  If there is no God, there can be no such thing as objective moral values.  We might choose to call certain behaviors “good” and certain behaviors “evil,” but such ascriptions are subjective determinations by human communities; i.e. they merely describe the beliefs and preferences of human subjects, not some object that exists transcendent to them.

The question, then, is not how we know what is moral, but how we make sense of the existence of moral values in the first place.  From whence do they come?  Why do they exist?  The moral argument provides an answer: Objective moral values are grounded in the very nature of God Himself.  The atheist’s response completely side-steps the question of moral ontology, choosing to focus on the much simpler question of moral epistemology.  We can grant to the atheist that belief in God is not necessary to know moral truths and behave morally, but this observation tells us nothing about why moral truths exist in the first place.

The second problem is related to, but distinct from the first.  It is non-sequitur to think that because one can know moral truths and behave morally without believing in God, God is not necessary to explain morality.  This is like saying that because one is able to read books without believing in authors, authors are not necessary to explain books.  In the same way books need authors, moral laws need a moral-law giver.