Metaethics is the study of the nature of ethical properties and statements. It includes questions about the sort of evidence which can be used to support moral ideas, whether morality is culturally relative, and what the nature of moral facts could be.
Two major positions in metaethics are moral realism and moral antirealism. Moral realism has a number of forms, including:
Moral naturalism: The claim that moral truths are reducible to natural facts in the world.
Moral non-naturalism: The claim that moral trust are unusual types of truths (perhaps equivalent in nature to truths about mathematics).
Moral anti-realism also has a number of forms, including:
Moral error theory: The view that people’s moral practice and language commit them to mind-independent moral truths, but that there are no such truths.
Moral non-cognitivism: The view that moral practice does not commit people to mind-independent moral truth. Moral Non-Cognitivists argue that moral practice is properly understood as an expression of people’s values.
Lutz, Matthew & James Lenman (2018) Moral naturalism, Stanford Encyclopedia of Philosophy, May 30 (updated 21 December 2021).
Joyce, Richard (2007) Moral anti-realism, Stanford Encyclopedia of Philosophy, July 30 (updated 25 October 2016).
Ridge, Michael (2003) Moral non-naturalism, Stanford Encyclopedia of Philosophy, February 1 (updated 21 August 2019).
Sayre-McCord, Geoff (2005) Moral realism, Stanford Encyclopedia of Philosophy, October 3 (updated 31 October 2020).
Sayre-McCord, Geoff (2007) Metaethics, Stanford Encyclopedia of Philosophy, January 23 (updated 28 April 2014).
van Roojen, Mark (2004) Moral cognitivism vs. non-cognitivism, Stanford Encyclopedia of Philosophy, January 23 (updated 28 June 2018).