What Is the Error Theory? Mackie's Moral Skepticism

Direct Answer

The error theory is the metaethical view that moral judgments are systematically and uniformly false. Its most famous defender is J.L. Mackie, who set it out in Ethics: Inventing Right and Wrong (1977). The theory has a two-part structure. The conceptual claim is that our moral judgments presuppose the existence of objective values — values that are part of the fabric of the world, independent of human attitudes, and that carry "objective prescriptivity": they do not merely describe how things are but command how things ought to be. When we say "torture is wrong," we take ourselves to be stating a fact about an objective wrongness that exists in the world. The ontological claim is that there are no such things. The world is a world of natural facts, and the "objective prescriptivity" that moral language presupposes is nowhere to be found. Therefore, every positive moral judgment is false: not because we sometimes get morality wrong, but because the very subject matter of morality does not exist. Moral discourse is a systematic error.

Historical Context

The error theory is the culmination of a skeptical tradition within modern ethics. David Hume had argued that moral distinctions are grounded in sentiment rather than reason — a view that already threatened the objectivity of morals. The theory's immediate ancestor is the is-ought problem: if no "ought" can be derived from any "is," then the normative element of moral claims cannot be a feature of the natural world. G.E. Moore had argued that "good" is a non-natural property; Mackie agreed with Moore that moral properties are not natural properties but drew the opposite conclusion — if moral properties are not natural, and there is nothing beyond the natural, then there are no moral properties at all. Mackie's error theory thus occupies a distinctive place in the map of metaethics: it is cognitivist (moral judgments are beliefs capable of truth and falsehood), realist in its analysis of moral language (moral claims purport to state objective facts), but anti-realist in its ontology (there are no such facts). The theory made moral nihilism a respectable philosophical position and generated a vast literature of responses.

Key Arguments & Debates

Mackie offered two main arguments. The argument from relativity (or disagreement) observes that moral codes vary enormously across cultures and eras, and argues that this diversity is best explained by the hypothesis that moral beliefs are projections of cultural practices rather than perceptions of objective facts — people approve of what their society has taught them to approve. The argument from queerness is more famous. Objective values, Mackie argued, would have to be "queer" entities: utterly unlike the natural properties science studies, they would have to be intrinsically prescriptive — commanding us, as it were — and we would need a strange faculty of moral intuition to perceive them. Since we have no reason to believe in such entities or such a faculty, we should conclude that objective values do not exist. The arguments have drawn powerful responses. Realists such as Peter Railton and Thomas Nagel argue that the naturalist can accommodate moral facts without queerness, or that normativity is not queer at all but is central to practical reason. Intuitionists reply that non-natural normative knowledge is no queerer than mathematical knowledge. Critics also point out that the error theory faces its own problems: it must explain how moral discourse could be so systematically mistaken, and what we should do with a morality that is false but indispensable.

Contemporary Relevance

The error theory matters because it is the starkest form of the claim that morality is an illusion. If true, it would have radical consequences: moral responsibility, human rights, and moral criticism would all rest on false presuppositions, and the practical question would become what to do with a false but useful moral discourse. Mackie himself suggested a "second-order" solution: we might continue to use moral language as a useful fiction. Contemporary philosophers continue to debate whether error theory is true, whether "moral fictionalism" is coherent, and whether some moral claims survive the error-theoretic purge. The theory also sharpens the popular intuition that "morality is an invention" — showing exactly what would follow if that intuition were right, and exactly what it would cost.

Related Concepts

The error theory is the paradigmatic form of moral nihilism and the most radical member of the anti-realist family. It is closely tied to moral skepticism and to the is-ought problem. It inverts Moore's non-naturalism: both agree moral properties are not natural; Moore concluded they exist, Mackie concluded they do not.

Further Learning

The Stanford Encyclopedia of Philosophy's entry on moral skepticism covers the error theory in depth. The Internet Encyclopedia of Philosophy's entry on moral realism situates it in the realism debate. Mackie's Ethics: Inventing Right and Wrong (Penguin, 1977) is the primary text.