Metaethics, understood as a distinct branch of ethics, is often traced to G. E. Moore's 1903 classic, Principia Ethica. Whereas normative ethics is concerned to answer first-order moral questions about what is good and bad, right and wrong, metaethics is concerned to answer second-order non-moral questions about the semantics, metaphysics, and epistemology of moral thought and discourse. Moore has continued to exert a powerful influence, and the sixteen...