ExpressivismIn meta-ethics, expressivism is a theory about the meaning of moral language. According to expressivism, sentences that employ moral terms – for example, "It is wrong to torture an innocent human being" – are not descriptive or fact-stating; moral terms such as "wrong", "good", or "just" do not refer to real, in-the-world properties. The primary function of moral sentences, according to expressivism, is not to assert any matter of fact but rather to express an evaluative attitude toward an object of evaluation.
Cognitivism (ethics)Cognitivism is the meta-ethical view that ethical sentences express propositions and can therefore be true or false (they are truth-apt), which noncognitivists deny. Cognitivism is so broad a thesis that it encompasses (among other views) moral realism (which claims that ethical sentences express propositions about mind-independent facts of the world), ethical subjectivism (which claims that ethical sentences express propositions about peoples' attitudes or opinions), and error theory (which claims that ethical sentences express propositions, but that they are all false, whatever their nature).
Quasi-realismQuasi-realism is the meta-ethical view which claims that: Ethical sentences do not express propositions. Instead, ethical sentences project emotional attitudes as though they were real properties. This makes quasi-realism a form of non-cognitivism or expressivism. Quasi-realism stands in opposition to other forms of non-cognitivism (such as emotivism and universal prescriptivism), as well as to all forms of cognitivism (including both moral realism and ethical subjectivism).
Moral realismMoral realism (also ethical realism) is the position that ethical sentences express propositions that refer to objective features of the world (that is, features independent of subjective opinion), some of which may be true to the extent that they report those features accurately.
EmotivismEmotivism is a meta-ethical view that claims that ethical sentences do not express propositions but emotional attitudes. Hence, it is colloquially known as the hurrah/boo theory. Influenced by the growth of analytic philosophy and logical positivism in the 20th century, the theory was stated vividly by A. J. Ayer in his 1936 book Language, Truth and Logic, but its development owes more to C. L. Stevenson. Emotivism can be considered a form of non-cognitivism or expressivism.
Non-cognitivismNon-cognitivism is the meta-ethical view that ethical sentences do not express propositions (i.e., statements) and thus cannot be true or false (they are not truth-apt). A noncognitivist denies the cognitivist claim that "moral judgments are capable of being objectively true, because they describe some feature of the world". If moral statements cannot be true, and if one cannot know something that is not true, noncognitivism implies that moral knowledge is impossible.
Moral skepticismMoral skepticism (or moral scepticism in British English) is a class of meta-ethical theories all members of which entail that no one has any moral knowledge. Many moral skeptics also make the stronger, modal claim that moral knowledge is impossible. Moral skepticism is particularly opposed to moral realism: the view that there are knowable and objective moral truths. Some defenders of moral skepticism include Pyrrho, Aenesidemus, Sextus Empiricus, David Hume, J. L.
MetaethicsIn metaphilosophy and ethics, metaethics is the study of the nature, scope, and meaning of moral judgment. It is one of the three branches of ethics generally studied by philosophers, the others being normative ethics (questions of how one ought to be and act) and applied ethics (practical questions of right behavior in given, usually contentious, situations).