Judgments to the effect that certain things (or certain classes of things) are good or bad, right or wrong, or just or unjust, are first-order ethical judgments. Metaethics addresses second-order questions about the meaning and status of moral judgments, for example, "What does it mean to say that something is good or bad, or right or wrong?", "Are moral judgments statements that purport to be true or false?", and "In what sense, if any, can moral judgments be true or false (or correct or incorrect)?" Metaethical questions have been discussed throughout the history of philosophy, but systematic work on metaethics began early in the twentieth century with the publication of G. E. Moore's Principia Ethica (1993).

The first half of this entry discusses theories about the meaning of moral judgments, specifically, Moore's theory, the Franz Brentano–A. C. Ewing (1899–1973) theory, emotivism, Richard Hare's prescriptivism, Philippa Foot's theory normative relativism...