Abstract

Contractualism and rule consequentialism both hold that whether a moral principle is true depends on what would happen if it were generally adopted as a basis for conduct. This paper argues that theories with this feature face a profound epistemic problem. The question of what would happen if different moral principles were generally adopted is a complex empirical question, comparable in difficulty to the question of what would happen if a nation adopted different laws, or if humanity had evolved different traits. Reflection on the epistemic demands of this question shows that we have no clue what would happen if different moral principles were generally adopted, and thus no clue what moral principles contractualism and rule consequentialism endorse. The only way to avoid cluelessness is to test principles on groups small enough to be epistemically tractable, which requires accepting an implausibly extreme form of moral relativism. I conclude that we must reject contractualism, rule consequentialism, and any other moral theory that entails that the truth of a moral principle depends on what would happen if it were generally adopted.