Two very different theories agree that morality doesn’t originate with human preference. They disagree about where it does.
Popular debate about religious ethics tends to collapse into one binary: either morality comes from God by command, understood as arbitrary, “because I said so,” or morality is secular and reasoned. This flattens two distinct, long-argued positions within religious ethics itself into a single caricature.
Divine Command Theory holds that an act is morally obligatory if and only if God has commanded it, so the commanding itself is what makes the act right, not some independent standard God is merely reporting on. Its classic objection, the Euthyphro dilemma, asks whether God commands what’s good because it’s already good, or whether it’s good only because God commands it. Contemporary defenders such as Robert Adams answer by limiting the theory to obligation specifically, and by grounding “good” in God’s own nature rather than an arbitrary decree.
Natural Law Theory, most fully developed by Thomas Aquinas, takes a different route to the same non-arbitrary conclusion. Morality is grounded in human nature and the ends that nature is oriented toward, ends a rational person can discover and reason about, not merely receive as command. On this view, God’s role is as the creator of that nature and its rational order, rather than the direct issuer of each specific moral rule.
The two traditions share the same underlying claim against moral relativism: that morality isn’t just a human convention that could have gone any other way. They differ on the mechanism, direct command versus rational nature, not on that shared premise.
Source: Stanford Encyclopedia of Philosophy, “Theological Voluntarism” and “The Natural Law Tradition in Ethics” (plato.stanford.edu).