, Volume 75, Issue 1, pp 137–146 | Cite as

Moore on Twin Earth

  • Neil LevyEmail author
Original Article


In a series of articles, Terry Horgan and Mark Timmons have argued that Richard Boyd’s defence of moral realism, utilizing a causal theory of reference, fails. Horgan and Timmons construct a twin Earth-style thought experiment which, they claim, generates intuitions inconsistent with the realist account. In their thought experiment, the use of (allegedly) moral terms at a world is causally regulated by some property distinct from that regulating their use here on Earth; nevertheless, Horgan and Timmons claim, it is intuitive that the inhabitants of this world disagree with us in their moral claims. Since any disagreement would be merely verbal were the alleged moral facts identical to or constituted by different natural facts, the identity or constitution claim must be false. I argue that their argument fails. Horgan and Timmons’ thought experiment is underdescribed; when we fill out the details, I claim, we shall see that the challenge to moral realism fades away. I sketch two possible interpretations of the (apparently) moral claims of the inhabitants of moral Twin Earth. On one interpretation, they fail to disagree with us because they actually agree with us; on the other, they fail to disagree with us because they are not moralizers at all. Which interpretation is true, I argue, will depend on the facts that explain the differences between us and the inhabitants of moral twin Earth.


Thought Experiment Moral Theory Natural Property Psychological Difference Moral Claim 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



I would like to thank two anonymous referees for Erkenntnis.


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Copyright information

© Springer Science+Business Media B.V. 2010

Authors and Affiliations

  1. 1.Oxford Centre for NeuroethicsOxfordUK
  2. 2.Florey Neuroscience InstitutesCarlton SouthAustralia

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