Analytical Moral Functionalism Meets Moral Twin Earth

In chapters 4 and 5 of his 1998 book From Metaphysics to Ethics: A Defence of Conceptual Analysis, Frank Jackson propounds and defends a form of moral realism that he calls both 'moral functionalism' and 'analytical descriptivism'. This chapter argues that this metaethical position, referred to as 'analytical moral functionalism', is untenable. It does this by applying a generic thought-experimental deconstructive recipe that has been used against other views that posit moral properties and identify them with certain natural properties - a recipe that is applicable to virtually any metaphysically naturalist version of moral realism. The recipe deploys a scenario called Moral Twin Earth.