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At the heart of metaethics lies a distinctively philosophical pressure: when people say that slavery is wrong or that kindness is good, are they stating truths about a mind-independent moral reality, or are they doing something else entirely — expressing emotions, issuing commands, or projecting attitudes? This question, which asks about the nature of moral language and thought rather than about which actions are right, has generated a sequence of competing frameworks spanning nearly a millennium.
Theological Voluntarism (1200–present) offered the first systematic answer: moral facts are grounded in God's commands or will. This view, associated with medieval thinkers such as Duns Scotus and later with the Protestant Reformation, faces the classic dilemma posed in Plato's Euthyphro: is something good because God commands it, or does God command it because it is good? The first horn threatens arbitrariness, the second implies a standard independent of God's will. This dilemma motivated subsequent frameworks to seek moral foundations elsewhere.
Ethical Intuitionism (1700–present), developed by philosophers like Samuel Clarke and later Henry Sidgwick, claimed that fundamental moral truths are self-evident to a rational faculty of intuition. In contrast to Theological Voluntarism, Intuitionism made morality independent of divine authority, grounding it in reason. However, this raised the question: if moral truths are self-evident, why do different people intuit different moral principles?
Moral Sentimentalism (1711–present), articulated by David Hume and Adam Smith, offered a rival account. Against Intuitionism's rationalism, Sentimentalism held that moral judgments arise from emotions or sentiments, not reason. Hume famously argued that reason is and ought to be the slave of the passions. This view did not reject moral objectivity entirely — Hume himself thought certain sentiments were universally shared — but it shifted the source of morality from reason to feeling, setting the stage for later non-cognitivist theories.
In 1903, G.E. Moore's Principia Ethica transformed metaethics. Moore argued that any attempt to define 'good' in natural terms (e.g., as pleasure or evolutionary fitness) commits the 'naturalistic fallacy' — it confuses a non-natural quality with natural properties. Moral Naturalism (1903–present), which claimed moral facts are natural facts, was thus dealt a severe blow. Moore's attack revived Ethical Intuitionism by arguing for a non-natural, irreducible moral property, and it forced naturalists to develop more sophisticated responses (such as the Cornell Realism of Boyd and Brink later in the 20th century).
The perceived failure of intuitionism — that intuitions vary and seem epistemologically mysterious — led to a radical alternative: Emotivism (1933–1965). A.J. Ayer and C.L. Stevenson argued that moral sentences do not express beliefs at all; they express emotions (Ayer) or attitudes (Stevenson). 'Murder is wrong' is not a truth-apt statement but an expression of disapproval. Emotivism reacted sharply against Intuitionism by denying that there are moral truths to be intuited.
Prescriptivism (1952–1980), developed by R.M. Hare, refined emotivism's insight while addressing its weaknesses. Hare argued that moral language functions not merely to express emotions but to prescribe universalizable norms. 'Stealing is wrong' means 'Do not steal' — a command addressed to all. Prescriptivism coexisted with Emotivism as a cognitivist alternative (since prescriptions are not truth-apt), but it avoided the charge that emotivism made moral disagreement irrational. Hare's universalizability criterion allowed for logical debate over prescriptions.
By the 1970s, dissatisfaction with non-cognitivism's apparent inability to account for moral truth and objectivity spurred a return to cognitivism. Moral Realism (1970–present) reasserted that moral claims are truth-apt and that at least some of them are true, corresponding to mind-independent moral facts. Realists divide into naturalists (e.g., Peter Railton, Richard Boyd) who locate moral facts in natural properties, and non-naturalists (e.g., Derek Parfit, David Enoch) who retain Moore's idea of irreducible moral properties.
Realism's return met immediate opposition from two related positions. Error Theory (1977–present), famously defended by J.L. Mackie, agreed with realists that moral claims are truth-apt but argued they are systematically false — there are no objective moral properties. Mackie's 'argument from relativity' and 'argument from queerness' sought to show that moral realism is metaphysically implausible. Moral Skepticism (1977–present) goes further, questioning whether we can have moral knowledge even if moral truths exist.
Moral Relativism (1960–present) offers a different anti-realist path: moral truth is relative to culture or individual perspective. Unlike Error Theory, which denies all moral truth, Relativism allows that moral claims can be true or false relative to a framework. This view gained traction in anthropology and public discourse but faces the charge that it undermines cross-cultural moral criticism.
The late 20th century saw a burst of innovation that deepened and diversified the metaethical landscape.
Expressivism (1984–present), pioneered by Simon Blackburn and Allan Gibbard, emerged from the ashes of emotivism and prescriptivism. Expressivism holds that moral sentences express non-cognitive mental states (e.g., plans or attitudes) but it develops a sophisticated semantic theory that explains how moral discourse can appear truth-apt without actually being about mind-independent facts. Unlike earlier emotivism, which treated moral language as mere venting, expressivism accounts for moral inference, disagreement, and embedding in complex sentences.
Quasi-Realism (1984–present), also developed by Blackburn, is a program that builds on expressivism. It aims to 'earn' realist-sounding features of moral discourse — talk of truth, facts, and knowledge — from an expressivist base without committing to metaphysical realism. Quasi-realists accept that our moral practices involve projecting attitudes onto the world; but by explaining how such projection yields a robust discourse, they try to capture the benefits of realism while avoiding its ontological commitments.
Metaethical Constructivism (1980–present), influenced by John Rawls and later developed by Christine Korsgaard and Sharon Street, competes with Moral Realism by arguing that moral truth is not discovered but constructed from a practical standpoint. According to constructivists, moral norms are those that would be agreed upon under certain idealized conditions (e.g., Rawls's original position). Unlike realists, constructivists deny that moral facts exist independently of our practical reasoning.
Reasons Internalism (1979–present), associated with Bernard Williams, addresses the link between morality and motivation. Internalism claims that for a moral reason to apply to an agent, it must be capable of motivating that agent — that is, it must be internal to the agent's subjective motivational set. This contrasts with externalism, which holds that moral reasons can apply regardless of motivation. The debate has profound implications for moral realism and practical rationality.
Moral Fictionalism (2001–present), proposed by Mark Kalderon and others, agrees with Error Theory that moral claims are systematically false but recommends a different response: we should continue to use moral discourse as a useful fiction. Unlike error theorists who might advocate abolition of moral talk, fictionalists treat moral statements as if they were true, engaging in a pretense that serves practical ends. This framework carves a middle ground between full-fledged realism and error-theoretic abolitionism.
Today, the leading frameworks are Moral Realism, Expressivism (often combined with Quasi-Realism), and Metaethical Constructivism. These three compete over the nature of moral truth: realists insist on mind-independent facts; expressivists deny truth-aptness in the robust sense but mimic it; constructivists argue that truth is a product of practical reasoning. There is broad agreement that metaethics must account for moral disagreement, motivation, and the appearance of objectivity. Disagreement persists over whether moral facts are part of the fabric of the universe or practical projections. The field remains divided between cognitivism and non-cognitivism, realism and anti-realism, with sophisticated variants that blur the boundaries — a sign that the central tension is still alive and productive.