Moral naturalism, as I use the term here, is the view that there are moral facts in the natural world – facts that are both natural and normative – and that moral claims are true or false in virtue of their corresponding or not to these natural facts. Moral naturalists argue that, since moral claims are about natural facts, we can establish the truth about moral claims through empirical investigation. Moral knowledge, on this view, is a form of empirical knowledge.
One objection to this metaethical view is that even if moral naturalists are correct in their claims about truth, they cannot answer the question of normativity. Jean Hampton, for instance, argues that it is not enough to explain the conduct's wrongness by showing it to be a property that necessarily supervenes on natural properties. For nothing in this analysis explains the relationship between these properties and us. The question is why should people care about these properties. Christine Korsgaard claims that moral realists take the normative question to be one about truth and knowledge.