What Is the Naturalistic Fallacy? Definition & Examples

Direct Answer

The naturalistic fallacy is the error of defining the moral property goodness in terms of a natural property. It was identified and named by G.E. Moore in Principia Ethica (1903). Moore argued that "good" is a simple, non-natural, unanalyzable property. Just as you cannot define "yellow" for someone who has never seen it, you cannot define "good" in terms of anything else: any proposed definition — "good is pleasure," "good is what we desire to desire," "good is evolutionary fitness" — misidentifies the property it attempts to define. Moore's argument for this claim is the open-question argument. Take any candidate definition, say "the good is the pleasant." Now ask: "This is pleasant, but is it good?" The question is open and meaningful — it is not like asking "This is a bachelor, but is he unmarried?" where the answer is given by the definition itself. The persistent openness of such questions shows, Moore concluded, that goodness is never identical with any natural property, and that defining it so commits the naturalistic fallacy.

Historical Context

The naturalistic fallacy entered philosophy in 1903 as part of Moore's assault on the ethical theories of his predecessors. The utilitarians — Jeremy Bentham and John Stuart Mill — had identified the good with pleasure or happiness; evolutionary ethicists identified it with fitness; the idealists identified it with self-realization. Moore claimed that all such theories commit the same mistake: they define "good" in terms of something else. The broader background is the is-ought problem of David Hume, who had noticed the slide from descriptive "is" statements to normative "ought" statements. Moore's fallacy is related but distinct: Hume flagged a logical gap between facts and values, while Moore claimed a definitional error in identifying value with fact. For the first half of the twentieth century, the naturalistic fallacy was widely treated as a decisive refutation of naturalistic ethics, until the naturalist revival — associated with philosophers such as Philippa Foot, Peter Railton, and the Cornell realists — argued that the fallacy charge misfires.

Key Arguments & Debates

The naturalistic fallacy is not a fallacy in the ordinary sense — it is not a mistake in inference but, Moore claims, a mistake in definition. The debate turns on the open-question argument. Non-naturalists defend Moore: the openness of the question reveals a real gap between goodness and any natural property, and no quantity of empirical investigation could ever establish that pleasure is goodness the way science established that water is H2O. Naturalists respond in several ways. First, the open-question argument proves too much: before science, the question "this is H2O, but is it water?" was open, yet water turned out to be H2O; openness reflects a limitation of our concepts, not a deep metaphysical gap. Second, naturalists argue that moral terms can be analyzed in terms of natural facts about well-being or rationality without losing their normative force. Third, some — like Peter Railton — develop naturalistic reductions of moral properties that preserve objectivity while answering Moore's challenge. The debate also connects to the is-ought problem: if Moore is right, the gap between facts and values is unbridgeable by definition; if the naturalists are right, it can be bridged.

Contemporary Relevance

The naturalistic fallacy remains a live issue whenever someone tries to ground ethics in science. Debates about evolutionary ethics, the science of well-being, and the neuroscience of morality all face the charge of committing it: a naturalist who says "morality is what promotes reproductive fitness" or "the good is what maximizes happiness" must answer Moore's question — "that may promote fitness, but is it good?" The fallacy also matters for everyday reasoning: the popular move from "this is natural, therefore it is good" is a distant cousin of the naturalistic fallacy, as is the inference from "this is how humans evolved to behave" to "this is how humans ought to behave." Understanding the fallacy helps you see what is missing in such arguments — the normative premise that connects the facts to the value.

Related Concepts

The naturalistic fallacy is intimately connected to the is-ought problem, with which it is often confused. It is the central weapon of moral non-naturalism against moral naturalism, and it originates in the work of G.E. Moore, whose Principia Ethica remains the classic text. The whole debate belongs to metaethics.

Further Learning

The Internet Encyclopedia of Philosophy's entry on G.E. Moore explains the naturalistic fallacy and the open-question argument clearly. The Stanford Encyclopedia of Philosophy's entry on moral non-naturalism covers the contemporary debate. Moore's Principia Ethica (Cambridge University Press, 1903) is the primary text.