LogicalMANIPULATIVE

Naturalistic Fallacy and the Is-Ought Gap

What it is

Two related errors that are often run together: deriving a value conclusion (ought) from purely factual premises (is) with no bridging value premise, and defining “good” as some natural property such as pleasant, evolved, or natural.

How it works

Hume (Treatise, Book III, Part I, Section I) observed that moral writers slide from propositions joined by “is” to propositions joined by “ought” without explaining how the new relation is derived; this is the is-ought gap. Moore (1903) argued something different: that any attempt to define “good” as a natural property — pleasure, survival, what evolution favors — fails the open-question test, since one can always sensibly ask whether that property is in fact good; he called this the naturalistic fallacy, and Frankena (1939) showed that it is really a fallacy of definition rather than of inference. Both are exploited the same way in persuasion: a description is delivered with the weight of a prescription. “Humans evolved to do this,” “it is natural,” “this is how markets work,” “that is just biology” invite the listener to supply the ought themselves, so the speaker never has to defend it. The honest error is forgetting the missing premise; the tactical use hides a contestable value judgment inside a factual claim, where it cannot be argued with. The tell is an ought that arrives with no value premise anywhere in the argument.

Real-world examples

  • •Herbert Spencer's phrase “survival of the fittest” (1864) was pressed into service by late-nineteenth-century Social Darwinists to argue that because competition eliminates the weak in nature, society ought not to protect them — a value conclusion drawn from a biological description (Hofstadter 1944).
  • •The mirror move on the left cites Kropotkin's Mutual Aid (1902), which documents cooperation among animals, as showing that a cooperative economic order is therefore right; the observation is sound and the inference identical in form.
  • •Food and wellness marketing runs on “natural” as a synonym for “good”: hemlock and arsenic are natural, and the missing premise (natural things are beneficial) is never stated because it could not survive being stated.
  • •Popular evolutionary-psychology writing sometimes concludes that because a behavior may once have been adaptive it is acceptable now; the same reasoning would license infanticide and coercion, which is the standard reductio.
  • •A manager defends an abusive workplace with “this is how the industry works” — a factual claim about prevalence doing the work of a claim about legitimacy.

Ethical guidelines

  • ●When you argue from a fact to a value, state the bridging value premise explicitly and defend it; that premise is the argument.
  • ●Do not use “natural,” “evolved,” or “how things are” as evaluations; they describe, and description settles nothing about what should be done.
  • ●Keep Hume and Moore distinct in your own reasoning: the gap concerns inference, the naturalistic fallacy concerns definition. Neither shows that facts are irrelevant to ethics, only that they are not sufficient.
  • ●Resist the reverse move as well: rejecting a fact because you dislike the value someone draws from it is the moralistic fallacy.

How to defend against it

  • ►Ask for the missing premise: “What value claim connects that fact to that conclusion?” Then argue about the premise, which is where the real disagreement lives.
  • ►Run the open-question test: “Suppose it is natural — is it therefore good?” If the question makes sense, the fact has not settled the value.
  • ►Offer the counterexample set: things that are natural and bad (disease), unnatural and good (anaesthesia), adaptive and wrong. The speaker must then say which natural things count and why — a value judgment.
  • ►Restate the argument in standard form with the ought on its own line; the gap is usually visible once the sentences are separated.
  • ►Concede the fact where it is true, then pivot: “Granting that, the question is what we should do about it,” which pulls the conversation back to an argument that can be had.

From the Defense Playbook

Name the Missing Premiseminutes

Most everyday arguments leave out the premise that does the real work; find it by asking what would have to be true for the stated reason to support the conclusion, say it aloud, and see whether anyone is still willing to assert it.

Every playbook entry states how strong its evidence is and when not to use it. Browse the full playbook.

References

  1. Hume, D. (1739). A Treatise of Human Nature, Book III, Part I, Section I (Books I-II published 1739; Book III published 1740). John Noon (Books I-II); Thomas Longman (Book III)
    The passage on the unexplained transition from is to ought that defines the is-ought gap.
  2. Moore, G. E. (1903). Principia Ethica. Cambridge University Press
    The naturalistic fallacy and the open-question argument against defining good as a natural property.
  3. Frankena, W. K. (1939). The naturalistic fallacy. Mind, 48(192), 464-477
    The clarification that Moore's fallacy is a definist fallacy, distinct from Hume's inferential point.
  4. Hofstadter, R. (1944). Social Darwinism in American Thought. University of Pennsylvania Press
    The Social Darwinist use of biological description as social prescription in the Spencer example.
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