In establishing that God exists, the cosmological and teleological arguments present the evidence in the world around us, whereas the moral and ontological arguments present the evidence in ourselves. Such evidence exists within ourselves because we are made in God's image.

The Argument

The best statement of the moral argument appears in C. S. Lewis's Mere Christianity. Briefly stated, a similar version of the argument goes as follows:

  1. Every human being has a sense of right and wrong, a conscience. We all understand what guilt is. Never has there been a human being who altogether escaped its accusing finger.

  2. We perceive moral value as objective rather than subjective. For example, if I see a vandal breaking a windshield, I perceive not only the incident itself but also its moral significance as external to my own mind. The car is real. The boy is real. The shattering of glass is real. Also, the wickedness of what the boy does is real. I see the wickedness as inherent in the vandalism, not as a product of my own judgment.

    Throughout every day we all have experiences of the same kind. We see something that triggers within us an immediate recognition of wrongdoing. The wrongness of it seems to reside in the offensive act itself, not in our personal view of the act. Upon reflection, we might decide that our judgment is subjective or even incorrect, but at the moment of the act, we have no doubt that the moral value we place on it is objective.

    Anyone who denies that he himself perceives moral value as objective may in fact be hampered by a defective conscience, or by a conscience so habitually suppressed that it no longer functions normally. Yet at the very least, every man unfailingly perceives that a correct opinion is good objectively, not just subjectively. That is, every man feels that it is truly and certainly good to be right. Any man without such a feeling would not care whether he was right or wrong. He would not defend himself. Nor would he speak at all, for all speech serves to promote an opinion.

  3. We rightly accept our moral perceptions as correct. In general, I believe something is real if I perceive it as real. Suppose I walk out of my garage and find a bicycle lying in the driveway. I have no doubt that it is there. I believe in its presence as firmly as I believe in anything. Why? Because my sense of vision has brought to my conscious mind an image of a bicycle. That image appears wholly objective; that is, it differs from images that I can readily identify as the work of dream or imagination. In every respect my perception of the bicycle points to something real. What do I conclude? Do I ponder the image and debate its significance? Do I question whether a bicycle is truly there? Do I feel that there are any grounds of doubt? Of course not. What I perceive leads directly to the conviction that I see a real bicycle. I come to this conviction without taking any intermediate steps of further scrutiny.

    The act of vandalism suggests a similar analysis. Before I believe the act to be wicked, I have already perceived it as wicked. The belief follows directly from the perception. Should I doubt my conclusion? In my interaction with the physical world, I trust my sensory perceptions for two reasons. First, I assume that my five senses have been built to assure correct results. Second, experience has shown that my perceptions are reliable. Why then should I not trust my moral perceptions? They are trustworthy for comparable reasons. First, it is a good assumption that whatever made my conscience certified that it would function correctly. Second, my conscience has always been a dependable guide to moral judgments.

    The analogy between sensory perception and moral perception therefore suggests that we have as much basis for believing that things are good or bad as for believing that things exist.

  4. The objectivity of moral value points to a Creator. How could there be objective moral value in a universe containing only matter in motion, evolving by chance? Such value could exist only in a universe created by a moral Being—that is, by God.

The Scriptural Basis

Paul teaches that there is not only a law written on parchment or paper, but also a law written on the heart, the second being the same as conscience.

14 For when the Gentiles, which have not the law, do by nature the things contained in the law, these, having not the law, are a law unto themselves:

15 Which shew the work of the law written in their hearts, their conscience also bearing witness, and their thoughts the mean while accusing or else excusing one another.

Romans 2:14-15

By whom is the law written on the heart? Paul does not answer the question explicitly, but clearly he means that the writer is God. Only a moral God could be the source of a moral detector like conscience. The righteousness of the source is reflected in how quickly conscience responds to things good and bad and in how keenly it feels the difference.