"[2] A metaethical theory, unlike a normative ethical theory, does not attempt to evaluate specific choices as being better, worse, good, bad, or evil; although it may have profound implications as to the validity and meaning of normative ethical claims.
Cognitivist theories hold that evaluative moral sentences express propositions (i.e., they are 'truth-apt' or 'truth bearers', capable of being true or false), as opposed to non-cognitivism.
Most forms of cognitivism hold that some such propositions are true (including moral realism and ethical subjectivism), as opposed to error theory, which asserts that all are erroneous.
Moral realism (in the robust sense; see moral universalism for the minimalist sense) holds that such propositions are about robust or mind-independent facts, that is, not facts about any person or group's subjective opinion, but about objective features of the world.
Non-cognitivist theories hold that ethical sentences are neither true nor false because they do not express genuine propositions.
[4][5] Non-centralism has been of particular importance to ethical naturalists in the late 20th and early 21st centuries as part of their argument that normativity is a non-excisable aspect of language and that there is no way of analyzing thick moral concepts into a purely descriptive element attached to a thin moral evaluation, thus undermining any fundamental division between facts and norms.
Allan Gibbard, R. M. Hare, and Simon Blackburn have argued in favor of the fact/norm distinction, meanwhile, with Gibbard going so far as to argue that, even if conventional English has only mixed normative terms (that is, terms that are neither purely descriptive nor purely normative), we could develop a nominally English metalanguage that still allowed us to maintain the division between factual descriptions and normative evaluations.
Metaethical relativists, in general, believe that the descriptive properties of terms such as "good", "bad", "right", and "wrong" do not stand subject to universal truth conditions, but only to societal convention and personal preference.
Amongst them, there are those who hold that moral knowledge is gained inferentially on the basis of some sort of non-moral epistemic process, as opposed to ethical intuitionism.
Metaethical theories that imply an empirical epistemology include: There are exceptions within subjectivism however, such as ideal observer theory, which implies that moral facts may be known through a rational process, and individualist ethical subjectivism, which holds that moral facts are merely personal opinions and so may be known only through introspection.
Empirical arguments for ethics run into the is-ought problem, which asserts that the way the world is cannot alone instruct people how they ought to act.
Plato and Immanuel Kant, prominent figures in the history of philosophy, defended moral rationalism.
David Hume and Friedrich Nietzsche are two figures in the history of philosophy who have rejected moral rationalism.
Recent philosophers who defended moral rationalism include R. M. Hare, Christine Korsgaard, Alan Gewirth, and Michael Smith.