Naturalistic Fallacy
G. E. Moore's charge that ethical naturalists confuse the goodness of a thing with some natural property of it — a fallacy he claimed his open question argument exposes.
The naturalistic fallacy is G. E. Moore's diagnosis in Principia Ethica (1903) of the error he attributed to all attempts to define the good in terms of natural properties — pleasure, evolutionary success, what we desire, what we approve. Moore's open question argument runs as follows: for any proposed natural definition of the good, one can always intelligibly ask whether the property in question is itself good, and the question remains substantively open. From this Moore concluded that the good cannot be identical to any natural property and is itself a simple, unanalyzable, non-natural property.
The argument has been enormously influential in twentieth-century metaethics, despite serious challenges. Frankena argued that Moore's argument trades on an ambiguity between definitional and substantive identity claims. The Cornell realists (Boyd, Brink, Sturgeon) defended a posteriori naturalist identification of moral and natural properties. Contemporary expressivism, error theory, and constructivism each respond to Moore's challenge differently. The naturalistic fallacy is sometimes confused with Hume's is-ought problem, but Moore's argument is logically distinct.
Moore's open question argument has had a long career of refinement and rebuttal. William Frankena's 1939 paper The Naturalistic Fallacy charged Moore with begging the question: Moore's argument turns on the assumption that any genuine identity claim must be obvious upon analysis, but a posteriori identity claims (water is H2O, the morning star is the evening star) are clearly substantive. The Cornell realists — Richard Boyd, David Brink, Nicholas Sturgeon — defended a posteriori naturalist identification of moral and natural properties analogous to scientific identifications.
The naturalistic fallacy is sometimes confused with Hume's is-ought problem. The two are logically distinct: Hume's claim is about deductive entailment between descriptive and normative propositions, while Moore's is about the conceptual analysis of moral terms. A philosopher could accept Hume's is-ought gap while rejecting Moore's argument against ethical naturalism, and vice versa. Contemporary metaethics — expressivism, error theory, constructivism, naturalism — each engages Moore's challenge differently.
How philosophers have framed naturalistic fallacy
| Philosopher | Position |
|---|---|
| G. E. Moore | Confusing the goodness of a thing with any natural property of it; the open question argument exposes the fallacy. |
| David Hume | Distinct but related: no descriptive premises can entail normative conclusions. |
| Henry Sidgwick | Anticipated Moore's worry; the concept of good cannot be reduced to any natural property without remainder. |
| Philippa Foot | Naturalist response: human goods are continuous with natural goods; the species-form grounds evaluation. |
Representative quotes
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G. E. Moore
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“Here is one hand, and here is another.”
Proof of an External World," Proceedings of the British Academy 25 (1939).
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David Hume
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“A wise man proportions his belief to the evidence.”
Section X: Of Miracles; Part I. 87
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Henry Sidgwick
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“The good of any one individual is of no more importance, from the point of view of the universe, than the good of any other.”
Book 3, chapter 13, section 3 (7th ed., 1907)
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Philippa Foot
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“The whole of moral philosophy, as it is now widely taught, rests on a contrast between statements of fact and evaluations. … If a man is given good evidence for a factual conclusion he cannot just refuse to accept the conclusion on the ground that in his scheme of things this evidence is not evidence at all. With evaluations, however, it is different. An evaluation is not connected logically with the factual statements on which it is based.”
Wikiquote
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