What Is Moral Supervenience? Definition & Significance

Direct Answer

Moral supervenience is the thesis that moral properties depend on non-moral properties in a specific way: if two objects, actions, or states of affairs are identical in all their non-moral properties, they must be identical in their moral properties as well. There can be no moral difference without a non-moral difference. Two acts cannot differ in rightness if they are exactly alike in every non-moral respect; two people cannot differ in virtue if they are exactly alike in their natural characteristics and circumstances. The thesis is usually stated as a modal claim: it is necessary that, for any x and y, if x and y are non-morally alike, they are morally alike. Supervenience is a relation of dependence, though a weak one: it says that moral properties cannot vary independently of non-moral properties, but it does not by itself say that moral properties are reducible to non-moral properties, nor does it specify which non-moral properties the moral supervenes on. It is best understood as a constraint — a necessary condition — on any acceptable moral metaphysics.

Historical Context

The idea behind supervenience is old, though the term is modern. The intuition that moral evaluation must track the facts of the case — that a change in moral assessment requires a change in the facts — is implicit in virtually all ethical theorizing from Aristotle onward. The explicit concept of supervenience was imported into philosophy from the moral philosophy of the mid-twentieth century, where it was used to characterize the relation between moral and non-moral properties, and then generalized across philosophy of mind and metaphysics in the 1970s. In metaethics, supervenience became central through the work of R.M. Hare, who argued that the supervenience of moral properties on non-moral properties is a logical feature of moral language: to call something good is to commit oneself to calling anything relevantly similar good. The thesis acquired new significance in the debate over non-naturalism: if moral properties are non-natural, their necessary dependence on natural properties stands in need of explanation. Contemporary discussion, following Saul Kripke and Hilary Putnam's work on natural kinds, treats supervenience as a core tool for analyzing the relation between the normative and the natural.

Key Arguments & Debates

Supervenience is not itself a theory of morality; it is a constraint that any theory must satisfy, and the interesting debates concern what follows from it. The first debate asks whether supervenience entails realism. It does not: anti-realists can accept supervenience. A non-cognitivist can say that moral judgments supervene on non-moral judgments because it is a rule of moral discourse that moral assessment must be grounded in facts; an error theorist can accept supervenience as part of the (false) presuppositions of moral discourse. The second debate concerns the explanation of supervenience. Naturalists explain it by reduction: moral properties are natural properties, so their dependence on the natural is trivial. Non-naturalists cannot take this route, and critics such as J.L. Mackie argue that the unexplained supervenience of non-natural properties on natural ones is part of what makes them "queer." Non-naturalists respond that supervenience is an irreducible but intelligible feature of normative reality, or that it follows from the conceptual connection between moral and natural descriptions. The third debate concerns the supervenience base: exactly which non-moral properties fix the moral properties — only intrinsic natural properties, or also relational ones such as history, consequences, and social context? The answer varies with one's normative theory.

Contemporary Relevance

Moral supervenience is a workhorse of contemporary metaethics. It is invoked in arguments about moral explanation (do moral properties causally explain anything?), about the reducibility of the normative to the natural, and about the possibility of a "morally inverted world." It also connects metaethics to metaphysics and the philosophy of science, where supervenience relations are used to analyze emergence and dependence. For the practicing ethicist, supervenience expresses a basic demand of rationality: consistent moral judgment requires treating relevantly similar cases alike. The thesis thus underlies arguments from analogy and the requirement of impartiality that run through all of normative ethics.

Related Concepts

Moral supervenience bears directly on moral non-naturalism, for which it is both a constraint and a challenge, and on moral naturalism, which explains it by reduction. It plays a role in the realism vs anti-realism debate, since both sides accept the thesis but explain it differently. Its home is metaethics, and its tools come from metaphysics.

Further Learning

The Stanford Encyclopedia of Philosophy's entry on supervenience provides the formal and historical background. The Internet Encyclopedia of Philosophy's entry on moral non-naturalism discusses supervenience as it bears on the non-naturalist program. R.M. Hare's The Language of Morals (Oxford University Press, 1952) contains the classic statement of the thesis.