Semantic arguments against moral naturalism

This thesis investigates the prospects of a position in metaethics called moral naturalism. Moral naturalism can be summarized as two claims. First, moral naturalism is a form of moral realism, which states that there are true moral claims that hold irrespectively of a person’s attitudes or beliefs. Second, moral naturalism claims that these moral claims are about properties that are part of the natural world. The central challenge facing moral naturalism is to explain how these moral properties fit into the natural world. Are moral properties reducible to, or identical with, natural properties? If so, is there a semantic explanation for why moral properties are related to some natural properties, and not others? Two major arguments, the Open Question Argument and the Moral Twin Earth Argument, have suggested that such a semantic explanation is not possible, which would make moral naturalism an implausible position to hold. This thesis investigates the prospects for moral naturalism by assessing the success of these arguments. The conclusions offered in this thesis are conservative. Both arguments turn out to depend on controversial, yet plausible, assumptions. In the case of the Open Question Argument, I argue that the success of the argument is sensitive to the form of moral naturalism under consideration; while it is fairly clear that it succeeds against reductive moral naturalism, it is less clear that it undermines non-reductive moral naturalism. It is clearer that the Moral Twin Earth Argument is successful, but it cannot categorically rule out every semantic explanation that the moral naturalist might advance.Arts, Faculty ofPhilosophy, Department ofGraduat