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Who commits the unnaturalistic fallacy?
  1. Kyle Ferguson
  1. Division of Medical Ethics, NYU Grossman School of Medicine, New York, New York, USA
  1. Correspondence to Dr Kyle Ferguson, Division of Medical Ethics, NYU Grossman School of Medicine, New York, New York, USA; kyle.ferguson{at}

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According to G E Moore,1 we commit the naturalistic fallacy when we infer ‘x is good’ from non-evaluative premises involving x such as ‘x is pleasant’ or ‘x is desired’. On Moore’s view, the mistake is to think that we can reduce moral goodness to anything else or explain it in any other terms. We cannot analyse ‘good’, Moore thought, because goodness is simple, non-natural and sui generis.

If Moore were alive today, and if he were to ask contemporary bioethicists the right questions, he would probably find that many of them commit the naturalistic fallacy when they move from empirical premises to normative conclusions or when they articulate complex notions of the good. Pugh et al 2 might commit the naturalistic fallacy themselves when they conclude that people with natural immunity to COVID-19 should be exempt from vaccine mandates because such exemptions would achieve desired public health benefits. Moore would probably find me guilty of committing the naturalistic fallacy if I were to present my arguments against such exemptions.

A reanimated Moore would find that the naturalistic fallacy pervades bioethics and public health. In contrast, as I shall argue, the unnaturalistic fallacy is probably nowhere to be found. In this commentary, I explain what the so-called unnaturalistic fallacy really is and raise doubts about whether anyone really commits it.

Decades after Moore published Principia Ethica, Bernard Williams observed that the naturalistic fallacy is unfortunately named since it is neither a fallacy (ie, an inferential mistake) nor an argumentative tendency unique to ethical naturalists.3 Ethical non-naturalists make the same mistake—if it is a mistake—when they move from, say, ‘x is commanded by the gods’ to ‘x is good’.

Just as Moore’s ‘naturalistic fallacy’ misnames, Pugh et al’s ‘unnaturalistic fallacy’ misleads. To be …

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  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests None declared.

  • Provenance and peer review Commissioned; internally peer reviewed.

  • Three examples: first, they characterise their article as ‘mak[ing] the case for recognising proof of natural immunity as an acceptable alternative to proof of vaccination’ (p. 2); second, when articulating their main thesis, they write, ‘if vaccine-induced immunity achieves a sufficient public health benefit to justify a vaccine mandate, [then] such mandates ought to consider evidence of recent infection as a sufficient basis for an exemption’ (ibid.); third, when posing their key question, which they answer in the affirmative, they ask, ‘whether, if a vaccine mandate is being applied, natural immunity would also achieve the public health benefits that are desired’ (p. 3).

  • Two examples: first, ‘for the purposes of immunity certification, those who have acquired immunity naturally are potentially equivalent to those who have acquired immunity through vaccination’ (p. 2, italics mine); second, ‘on the basis of existing data, it is plausible that naturally acquired immunity may be as good as vaccine-mediated immunity’ (p. 3, italics mine).

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