If objective moral truths exist - if some things are genuinely right or wrong regardless of opinion - then those truths require a foundation. The Moral Argument contends that God is the best explanation for the existence of objective moral values and duties.
This is a logically valid modus tollens argument. If you deny the conclusion, you must deny one of the premises. Most people find Premise 2 difficult to reject - which means the weight of the argument falls on Premise 1.
On a naturalistic worldview - one where only physical matter, energy, and natural laws exist - moral facts have no obvious home. Consider the alternatives:
Evolution explains why we have moral instincts but cannot explain why those instincts track truth. Natural selection favors survival-promoting behavior, not morally correct behavior. If our moral sense is merely a survival mechanism, we have no reason to think it reveals genuine moral facts. As philosopher Michael Ruse has candidly admitted: on a purely evolutionary account, morality is "an illusion fobbed off on us by our genes."
Social contract theories ground morality in agreements among rational agents. But agreements are contingent - they could have been different. A society that agreed to permit genocide would not make genocide right. Social contracts describe what people do agree to, not what they ought to agree to.
Some philosophers argue that moral truths exist as abstract, mind-independent facts - like mathematical truths. This is philosophically coherent, but it raises a deep problem: why would abstract moral facts have any authority over concrete beings? And how would purely physical creatures gain epistemic access to non-physical moral truths? Without a bridge between the abstract and the concrete, moral Platonism is incomplete.
In The Brothers Karamazov, Dostoevsky explores the idea that "without God, everything is permitted." This is not a claim about psychology (atheists can behave well) but about ontology: without a transcendent moral lawgiver, there is no objective standard by which any action can be called genuinely right or genuinely wrong.
Do objective moral facts exist? Consider test cases:
If you affirm any of these, you are a moral realist. And moral realism - the existence of objective moral facts - is the majority position among professional philosophers. A 2020 PhilPapers survey found that roughly 62% of philosophers accept or lean toward moral realism.
Note also that moral relativism is self-defeating. The claim "there are no objective moral truths" is itself presented as an objective truth about morality. The relativist cannot state their position without undermining it.
The oldest and most common objection to theistic ethics is the Euthyphro Dilemma (from Plato): "Is something good because God commands it, or does God command it because it is good?"
If the former, morality seems arbitrary. If the latter, morality is independent of God, making God irrelevant to ethics.
The standard theistic response takes neither horn. Morality is grounded in God's nature, not God's arbitrary will. God is essentially good - goodness is not something God decides but something God is. God's commands flow necessarily from his unchangeable character. This is known as the Modified Divine Command Theory, defended by Robert Adams and William Lane Craig.
"Atheists can be moral. You don't need God to be a good person."
Absolutely true - and the argument does not deny this. The Moral Argument is not about moral behavior (epistemology) but about moral ontology: what grounds the existence of moral facts? An atheist can know and follow moral truths just as a person who doesn't believe in mathematics can still add correctly. The question is what makes those truths true - not who can access them.
"The existence of moral disagreement shows morality is subjective."
Disagreement does not entail subjectivity. People disagree about history, physics, and mathematics - yet we don't conclude those fields are subjective. Moral disagreement can reflect ignorance, bias, or cultural conditioning without undermining the existence of moral truth. In fact, the very act of moral disagreement presupposes that there is a right answer being sought.
The standard theistic response to the Euthyphro Dilemma is:
The Moral Argument demonstrates that objective moral values and duties - which most people recognize and most philosophers affirm - require a transcendent ground. Naturalism, evolution, and social contracts cannot provide this ground. God's essentially good nature offers the most coherent foundation for the moral facts we all recognize.