The moral argument in Christianity

The moral argument for God is distinctly modern in its popular form, though its roots are ancient. Aquinas located moral norms in natural law grounded in God's rational nature. Kant famously built his moral argument around the need for a postulate guaranteeing the correspondence of virtue and happiness. But the versions most often encountered today are mid-twentieth-century products: C.S. Lewis's argument from conscience in Mere Christianity, and William Lane Craig's formalization in contemporary apologetic debate.

Craig's version is the cleanest: if God does not exist, objective moral values and duties do not exist; objective moral values and duties do exist; therefore, God exists. The argument turns on a claim about grounding: that genuine, binding moral facts require a personal, perfect lawgiver. Lewis's version is softer and more rhetorical — the observation that we find ourselves with a moral law we did not invent and cannot evade, which points to a lawgiver behind it. Alvin Plantinga, Paul Copan, and Baggett & Walls have developed more technical defenses.

Critics from Plato (Euthyphro) onward have pressed the dilemma: does God command actions because they are good, or are they good because God commands them? The first horn makes God redundant to morality; the second makes goodness arbitrary. Modern Christian philosophers — Adams's modified divine command theory, Linda Zagzebski's exemplarist virtue ethics — have produced sophisticated responses that locate goodness in God's character rather than will. Secular moral realists like Derek Parfit, Thomas Nagel, and Erik Wielenberg have countered that moral facts can be grounded without God — in the nature of rational agency, in platonic moral objects, or in supervenience on natural properties.