Moral Realism and Twin Earth PDF

ABSTRACT. This paper critically examines Terence Horgan and Mark Timmons' claim that a variant of Hilary Putnam's Twin Earth thought experiment involving "Moral Twin Earth" has the resources to undermine naturalistic moral realism. We discuss three arguments based on Moral Twin Earth: one intended to revive J. L. Mackie's argument from queerness, one intended to revive G. E. Moore's open question argument, and one based directly on Moral Twin Earth.  We argue that none of these arguments succeed. Moral Twin Earth cannot revive the classic arguments against ethical naturalism nor can it undermine naturalistic moral realism on its own.

Laurence, S., & Margolis, E. (1999). Moral Realism and Twin Earth. Facta Philosophica, 1:1, pp. 135-165.