Abstract
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.
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Notes
Kraemer (1990/1991) and, following him, Laurence et al. (1999) suggest a similar but broader claim: that it is possible to interpret the MTE thought experiment as suggesting that a higher-level functional property constitutes a common core of the theories true at both worlds. The scenario I sketch here is in fact only a special case of this broader claim: if the differences across worlds is explained by differences in psychologies this special case will pertain, but other differences across worlds would entail that the higher-level functional property has quite different realizers.
Something like this point is made by David Merli, who focuses not on the psychological differences between us and the inhabitants of MTE, but on the details of their moral practice. He argues that if moral practices on MTE are genuinely governed by different properties, this fact will cause differences in practices that would be ‘significant enough to undermine our conviction in the synonymy of moral and twin-moral terms’ (Merli 2002: 216). I think he is absolutely right, but clearly his (and my) intuition is not widely shared. It is therefore necessary to offer an additional argument, to bring those who haven’t accepted Merli’s point around.
References
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I would like to thank two anonymous referees for Erkenntnis.
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Levy, N. Moore on Twin Earth. Erkenn 75, 137–146 (2011). https://doi.org/10.1007/s10670-010-9263-x
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DOI: https://doi.org/10.1007/s10670-010-9263-x