Theory that value judgments, including moral judgments, do not state facts (though they appear to), but are expressions of emotions or attitudes.
The theory, a form of speech act theory, arose under the influence of logical positivism (though it had antecedents in the 18th century) because of the difficulties of finding verification conditions for such utterances, and the need to explain how they can affect behavior.
Emotivism is also a form of subjectivism, but must be distinguished from the subjectivist view that while value judgments do describe something, what they describe are not special moral and such-like facts but human attitudes, whether the speaker's own or other people's.
One obvious, though not necessarily insuperable, difficulty is that of accounting adequately for moral argument and moral disagreement.
Also see: Boo Hurrah Theory
C L Stevenson, Ethics and Language (1944)