The Naturalistic Fallacy: What Moore Got Right and Wrong

When G. E. Moore published Principia Ethica in 1903, he aimed a single sharp argument at nearly every ethical theory on the market. More than a century later, the wound it opened has not fully closed.

What Moore actually argued

Moore's target was any attempt to define "good" in terms of natural properties — pleasure, evolutionary fitness, social cohesion, divine command, or anything else observable or measurable. He called this the naturalistic fallacy, and his weapon against it was the open-question argument.

The argument runs as follows. Take any natural property N. However thoroughly you describe N, you can always sensibly ask: "Yes, but is N actually good?" That question never sounds obviously confused in the way that "Is a bachelor unmarried?" does. Because the question remains genuinely open, "good" cannot mean the same thing as N. To identify the two is to commit a fallacy.

Moore concluded that goodness is a non-natural, simple, indefinable property — real but not reducible to anything in the physical world. We apprehend it by a faculty he called moral intuition, in the same way we directly perceive the colour yellow without being able to decompose it further.

Where the argument has genuine force

The open-question argument does expose something important. Many ethical naturalists in Moore's day moved too quickly from descriptive claims to normative ones. A utilitarian who says "good just means pleasurable" has not thereby settled the question of whether pleasure is worth pursuing — they have assumed it. A Darwinian who equates morality with whatever promotes survival has not shown that survival matters; they have smuggled in a value judgment without acknowledging it.

This connects directly to Hume's is-ought gap, but Moore's version is sharper in one respect: it does not merely say you cannot derive ought from is, it says that no description of the natural world, however complete, will analytically contain the concept of goodness. That is a stronger and more interesting claim.

For atheists and secular ethicists in particular, the argument serves as a useful corrective. It is tempting to replace theological grounding with naturalistic grounding — to say that moral facts just are facts about human flourishing or preference satisfaction. Moore's challenge forces the question: even granting all those empirical facts, why should we act on them? The answer cannot simply be more facts.

Where Moore overreached

The conclusion Moore drew — that goodness is a non-natural, simple, indefinable property perceived by intuition — faces serious problems of its own.

First, the epistemology of moral intuition is deeply unclear. If goodness is non-natural, how do physical brains access it? Moore was never satisfactory on this point, and the move to intuition invites the same charge he levelled at others: it defers rather than explains.

Second, the open-question argument, pressed too hard, proves too much. Consider: you can ask "Is water really H₂O?" and the question sounds open to someone ignorant of chemistry. That does not mean water and H₂O are different things — it means the identity is a posteriori, not analytic. Contemporary ethical naturalists, following figures like Frank Jackson and Peter Railton, argue that moral properties may be identical to natural ones even if the identity is not knowable by pure conceptual analysis. Moore assumed that all genuine identities are definitional. That assumption is false.

Third, Moore's own positive view — ethical intuitionism — has an uncomfortable history. When intuitions conflict, as they do across cultures and individuals, there is no principled way to adjudicate between them. Claiming direct intuitive access to moral truth has repeatedly served to insulate prejudice from criticism.

What remains useful

The lasting contribution of Moore's argument is not its conclusion but its diagnostic function. It gives us a reliable red flag: whenever someone moves from a factual premise to a moral conclusion without showing why the factual property is the kind of thing that generates obligations or value, the naturalistic fallacy detector should fire.

This does not mean naturalistic ethics is hopeless. It means the work cannot be done by definition alone. A serious naturalistic ethics — such as those built around reflective equilibrium, constructivism, or second-order desires — acknowledges the gap and tries to bridge it through substantive argument rather than linguistic sleight of hand. Moore did not close that project; he clarified what it demands.

For anyone building an ethical framework without religious scaffolding, that clarification is genuinely useful. Secular ethics is not automatically better-grounded than religious ethics just because it appeals to nature or science. It still needs to answer why the natural facts it selects — suffering matters, flourishing matters, autonomy matters — carry normative weight. Moore was wrong about the metaphysics, but he was right that the question does not answer itself.