facts. It is usually defined in opposition to moral realism, which holds that there are objective moral values, such that a moral claim may be either true or false. Specifically the moral anti-realist is committed to denying one of the following three statements: The Semantic Thesis: Moral statements have meaning, they express propositions, or are the kind of things that can be true or false. The Alethic Thesis: Some moral propositions are true. The Metaphysical Thesis: The metaphysical status of moral facts is robust and ordinary, not importantly different from other facts about the world. Different version of moral anti-realism deny different statements: specifically, non-cognitivism denies the first claim, arguing that moral statements have no meaning or truth content, error theory denies the second claim, arguing that all moral statements are false, and ethical subjectivism denies the third claim, arguing that the truth of moral statements is mind dependent. Examples of anti-realist moral theories might be: Ethical subjectivism Non-cognitivism Emotivism Prescriptivism Quasi-realism Projectivism Moral fictionalism Moral nihilism Moral skepticism There is a debate as to whether moral relativism is actually an anti-realist position. While many versions deny the metaphysical thesis, some do not, as one could imagine a system of morality which requires you to obey the written laws in your country. Such a system would be a version of moral relativism, as different individuals would be required to follow different laws, but the moral facts are physical facts about the world, not mental facts, so they are metaphysically ordinary. Thus, different versions of moral relativism might be considered anti-realist or realist. Epistemic anti-realism Just as moral anti-realism asserts the nonexistence of normative facts, epistemic anti-realism asserts the nonexistence of facts in the domain of epistemology. Thus, the two are now sometimes grouped together as "metanormative anti-realism". Prominent defenders of epistemic anti-realism include Hartry Field, Simon Blackburn, Matthew Chrisman, and Allan Gibbard, among others. See also Arend Heyting Constructivist epistemology Crispin Wright Critical realism (philosophy of perception) Luitzen Egbertus Jan Brouwer Metaepistemology Münchhausen trilemma Neil Tennant (philosopher) Philosophical realism Quasi-realism References Bibliography . reprinted, pp. 1–24. . reprinted, pp. 145–165. . reprinted, pp. 202–214. Lee Braver (2007). A Thing of This World: a History of Continental Anti-Realism, Northwestern University Press: 2007. Ian Hacking (1999). The Social Construction of What?. Harvard University Press: 2001. Samir Okasha (2002). Philosophy of Science: A Very Short Introduction. Oxford University Press. External links Semantic challenges