Moral Error Theory

Core Idea

Moral error theory, associated with J.L. Mackie, holds that moral claims are genuine truth-apt propositions (unlike expressivism) but that they are all systematically false because they presuppose the existence of objective moral facts that do not exist. Moral language implicitly refers to queer, non-natural properties that could not survive Occam's razor; since nothing in the world answers to these presuppositions, every positive moral claim fails. Error theory is distinct from relativism (which makes morality relative to a framework) and from expressivism (which denies moral claims are truth-apt). A practical challenge is explaining why we should continue making and acting on moral judgments if they are all false.

How It's Best Learned

Read Mackie's chapter 'The Subjectivity of Values' in Ethics: Inventing Right and Wrong. Contrast with the expressivist response: instead of saying all moral claims are false, revise their semantics to make them non-truth-apt.

Common Misconceptions

• Error theory is not nihilism about values; it is a thesis about the truth conditions of moral language.
• Mackie was not claiming we should stop caring about ethics—he thought we should invent or construct moral systems knowing they lack objective grounding.

Explainer

From your study of metaethics and moral realism, you know the central debate: are there objective moral facts, and if so, what kind of things are they? Moral realists say yes — claims like "torture is wrong" are true in the same way "the Earth orbits the Sun" is true, independently of what anyone thinks or feels. From your study of expressivism, you know one anti-realist response: moral statements are not genuine truth-apt propositions at all — they are expressions of attitude, more like cheers or commands than factual claims. Moral error theory, associated primarily with J.L. Mackie, takes a third path that differs from both.

Mackie agrees with the moral realist about semantics: moral statements are genuine truth-apt propositions that purport to describe objective features of reality. He agrees with expressivists about the metaphysics: no such features exist. The result is a striking conclusion — every positive moral claim is *false*. Not false in the way "the Moon is made of cheese" is false (a factual error about a real domain), but systematically false because the entire domain of objective moral facts that moral language presupposes is empty. When you say "cruelty is wrong," you are implicitly claiming that cruelty has a property — wrongness — that is objective, non-natural, and intrinsically motivating. Since nothing in reality has such a property, your claim fails to refer to anything real.

Mackie's central argument for this conclusion is the argument from queerness. Objective moral facts, if they existed, would be deeply strange entities. They would be non-physical, not empirically detectable, yet somehow capable of motivating rational agents just by being perceived — a combination of metaphysical and epistemological properties that nothing else in our ontology resembles. We would need a special moral faculty to perceive them, a faculty with no clear natural explanation. Occam's razor argues against positing such entities: we can explain moral language, moral disagreement, and moral motivation without them, so we should not posit them.

The practical challenge this raises is often called the so what problem: if all moral claims are false, why should we continue making moral judgments or acting morally? Mackie's answer is important — he was not recommending the abandonment of ethics. He thought we should acknowledge that we *invent* moral systems rather than discover them, and that this invention is both necessary and worthwhile. Moral frameworks help coordinate behavior, resolve conflicts, and support human flourishing; they do not need metaphysical grounding to do that work. This distinguishes error theory from nihilism: error theory is a thesis about what moral language *presupposes*, not a recommendation for how to live. The error is in the presupposition, not in caring about ethics itself.