In 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. Because the function of moral language is non-descriptive, moral sentences do not have any truth conditions. Hence, expressivists either do not allow that moral sentences to have truth value, or rely on a notion of truth that does not appeal to any descriptive truth conditions being met for moral sentences.
Overview
Expressivism is a form of moral anti-realism or nonfactualism: the view that there are no moral facts that moral sentences describe or represent and no moral properties or relations to which moral terms refer. Expressivists deny constructivist accounts of moral truths – e.g., Kantianism – and realist accounts – e.g., ethical intuitionism.
Because expressivism claims that the function of moral language is not descriptive, it allows the realist to avoid an error theory: the view that ordinary ethical thought and discourse are committed to deep and pervasive error and that all moral statements make false ontological claims.
Distinction from descriptivist subjectivism
Expressivism does not hold that moral sentences, as used in ordinary discourse, describe the speaker's moral attitudes. Expressivists are united in rejecting ethical subjectivism: the descriptivist view that utterances of the type "X is good/bad" mean "I approve/disapprove of X". Subjectivism is a descriptivist theory, not an expressivist one because it maintains that moral sentences are used to represent facts – namely, facts about the subject's psychological states.
Historical development: from noncognitivism/emotivism to cognitivist expressivism
Some early versions of expressivism arose during the early twentieth century in association with logical positivism. These early views are typically called "noncognitivist". A. J. Ayer's emotivism is a well-known example.
According to emotivism, the act of uttering a moral sentence of the type "X is good (bad)" is closely akin to the expression of a positive (or negative) emotional attitude toward X, and such an utterance can be paraphrased by "Hurrah for X!" or "Boo, X!"
C. L. Stevenson also advanced an important version of emotivism.
At the beginning of the middle of the twentieth century, R. M. Hare was an important advocate of expressivism / noncognitivism. Hare's view is called prescriptivism because he analyzed moral sentences as universal, overriding prescriptions or imperatives. A prescriptivist might paraphrase "X is good" as "Do X!".
More recent versions of expressivism, such as Simon Blackburn's "quasi-realism", Allan Gibbard's "norm-expressivism", and Mark Timmons' and Terence Horgan's "cognitivist expressivism" tend to distance themselves from the "noncognitivist" label applied to Ayer, Stevenson, and Hare. What distinguishes these "new wave" expressivists is that they resist reductive analyses of moral sentences or their corresponding psychological states, moral judgments, and they allow for moral sentences/judgments to have truth value.
Horgan and Timmons' label "cognitivist expressivism" in particular captures the philosophical commitment they share with Blackburn and Gibbard to regard moral judgments as cognitive psychological states, i.e. beliefs, and moral sentences as vehicles for genuine assertions or truth-claims. Much of the current expressivist project is occupied with defending a theory of the truth of moral sentences that is consistent with expressivism but can resist the Frege-Geach objection (see below). Expressivists tend to rely on a minimalist or deflationary theory of truth to provide an irrealist account for the truth of moral sentences.
Arguments for
Open question argument
According to the open question argument (originally articulated by intuitionist and non-naturalist G. E. Moore), for any proposed definition of a moral term, e.g. " 'good' = 'the object of desire' ", a competent speaker of English who understands the meaning of the terms involved in the statement of the definition could still hold that the question, "Is the object of desire good?" remains unanswered.