In discussions about morality, one central question is whether objective moral facts need a deeper metaphysical grounding, and if so what kind. The question is especially important for philosophers who combine moral realism with a broadly naturalist worldview: roughly, the view that reality contains no supernatural agents or purposes and is continuous with the world investigated by the sciences. That need not mean crude reductionism; many naturalists allow higher-level facts in biology, psychology, economics, and ethics. This article examines the pressure point for naturalist moral realism and surveys serious secular responses, including Cornell realism, Peter Railton's naturalistic realism, and Derek Parfit's non-naturalist realism. It is also important to note proportion: many atheists are moral realists, and many are moral anti-realists, so atheism by itself does not settle the issue.
The Objectivity of Moral Facts
To steelman the position that moral facts are objective, we must first understand what is meant by "objective" in this context. An objective moral fact is one whose truth does not depend merely on individual preference, social approval, or cultural convention. Proponents need not claim that every moral rule is simple or exceptionless. Their core claim is that at least some moral truths, such as that deliberate cruelty for its own sake is wrong, remain true even if a person or society approves of them.
Philosophers who defend the objectivity of moral facts often argue that these facts can be known, at least imperfectly, and that they have normative significance: they count in favor of or against actions. This does not mean that recognizing a moral fact automatically motivates every person. A moral reason may remain a reason even when a selfish, apathetic, or morally damaged person feels no desire to act on it. This view is often contrasted with moral relativism, which makes moral truth dependent on cultural or individual standpoints, and moral nihilism, which denies that there are moral truths at all.
Naturalism and the Grounding Problem
Naturalism is best stated carefully. It is not simply the claim that every truth is currently reducible to physics, nor that only laboratory science can speak. A broad metaphysical naturalism says that the facts of reality are exhausted by the natural order and its law-governed entities, properties, and relations. The challenge for naturalists who affirm objective moral truths is to explain how normative facts fit into that order. Are moral facts identical with, constituted by, or supervenient on natural facts such as suffering, flourishing, agency, social cooperation, and reasons-responsive capacities? Or are they irreducible facts that a naturalist should still accept? This is the grounding problem: what makes moral facts true, and how do they relate to non-moral facts?
One influential critique comes from J.L. Mackie, who defended an error theory: ordinary moral discourse purports to state objective values, but there are no such values. His well-known "argument from queerness" had two parts. Metaphysically, objective values would be unlike ordinary natural properties because they would be objectively prescriptive: they would somehow have action-guiding authority built into them. Epistemologically, if such values existed, Mackie thought we would need a special faculty of moral intuition to know them. The force of the argument is not that moral realism is obviously false, but that realists owe an account of how normative authority and moral knowledge fit with the rest of what we believe about the world.
Naturalist Answers to the Grounding Problem
Several philosophers have proposed ways to reconcile objective moral truths with naturalism. One approach is Cornell realism, associated with Richard Boyd, Nicholas Sturgeon, and David Brink. Cornell realists usually do not say that goodness is analytically equivalent to some simple natural property, as if "good" just meant "pleasant" or "desired." Rather, they defend a synthetic or a posteriori form of moral naturalism: moral properties are natural properties or natural property-clusters that play an explanatory role in our best account of human life, social practice, and moral inquiry. On this view, moral properties supervene on natural properties: there cannot be a moral difference without some underlying natural difference. The debated question is whether moral properties genuinely explain anything, or whether all the explanatory work is already done by non-moral facts.
Peter Railton offers another naturalist realist account, often read as a sophisticated consequentialist or "ideal advisor" theory. For Railton, a person's non-moral good is connected to what that person would want for himself or herself under conditions of full information and instrumental rationality, with the facts vividly appreciated. Moral rightness then involves an impartial or social point of view that takes people's objective interests seriously. Railton's account is realist because the relevant facts can diverge from what any actual person or culture presently approves; it is naturalist because those facts concern human interests, information, rational agency, and consequences rather than supernatural commands.
Derek Parfit, meanwhile, offers a secular but non-naturalist approach, so his view should not be presented as a solution for strict naturalism. In On What Matters, Parfit argues that there are objective normative reasons: some facts really do count in favor of actions, beliefs, or desires independently of what we happen to want. He treats these truths as irreducibly normative, closer in status to logical or mathematical truths than to physical objects. The strength of this view is that it preserves robust objectivity without reducing morality to preference; the cost is that it asks us to accept non-natural normative truths in our ontology.
The Reply from Moral Anti-Realism
Many atheists adopt some form of moral anti-realism, but this is not the only atheist position; contemporary philosophy contains many secular moral realists as well. Anti-realists avoid the realist's grounding problem by denying that morality consists in stance-independent moral facts. Different versions explain moral language differently: some treat it as expressing attitudes, some as issuing prescriptions, some as constructed from rational procedures or social practices, and some as systematically in error. This can fit comfortably with naturalism, though it faces its own explanatory tasks.
For example, emotivism, associated with A.J. Ayer and C.L. Stevenson, holds that moral utterances primarily express approval or disapproval rather than report moral facts. Later expressivists and quasi-realists, such as Simon Blackburn and Allan Gibbard, try to explain why moral discourse can still look truth-apt, logical, and action-guiding without positing robust moral facts. Error theory, defended by Mackie and in a different contemporary form by Richard Joyce, says that ordinary moral discourse presents itself as objective but rests on a false presupposition. These are serious academic positions, not merely evasions of moral responsibility.
Weighing the Strengths and Limitations
Naturalist accounts that seek to ground objective morality face significant challenges, especially in explaining normativity: why certain natural facts about pain, flourishing, agency, or social relations count as reasons that we ought to respect. Cornell realism and Railton's theory are serious frameworks, not easy targets. Their critics argue that they may identify the natural conditions under which moral judgments arise or function without fully explaining why those conditions have authoritative normative force. Their defenders reply that this demand for an extra "authority-making" ingredient is itself suspect: perhaps moral authority is nothing over and above the relevant facts about creatures like us and the reasons those facts provide.
Parfit's non-naturalist but secular approach offers an intriguing alternative, yet it raises questions about the ontological status of these objective reasons and their relation to the physical world. For those committed to strict naturalism, this may be a significant hurdle.
The moral anti-realist position, while avoiding these issues, must contend with the implications of denying objective moral truths, such as addressing concerns about moral progress and disagreement.
In conclusion, naturalist accounts of objective morality are not obviously incoherent, but they face a real explanatory challenge: they must show how objective "oughts" fit within a natural picture of the world. Parfit-style non-naturalism avoids reduction but pays the price of positing irreducible normative truths. Anti-realism avoids robust moral facts but must explain moral practice, disagreement, blame, and progress without them. None of these results, by itself, proves theism or atheism. At most, the grounding debate shows that every worldview owes an account of moral objectivity, moral knowledge, and moral authority, and that weak popular dismissals of the problem do not do justice to the serious philosophical literature.