Abstract

Sidgwick argued that utilitarianism and egoism were in conflict, that neither theory was better justified than the other, and concluded that there was a and all that remained to him was. The dualism argument introduced by Sidgwick is an extremely powerful sceptical argument that no theory of ethics is rationally required: it cannot be shown that a moral sceptic or an egoist ought to accept the moral theory, otherwise she is unreasonable. I explain two ways in which the significance of the dualism argument has been underestimated. First, I suggest that a hybrid theory such as utilitarianism with an egoist bias is not a solution to the dualism. Second, I argue that the dualism argument is not restricted to a conflict between hedonic egoism and utilitarianism, but applies to any attempt to show that a theory of ethics is rationally required