Abstract In the wake of Locke’s Essay, empiricists faced the challenge of giving an empiricist account of the origins of moral knowledge. Locke did not rise to this challenge and relied on revelation as the source of moral knowledge. Other empiricists, including Hume and Hutcheson, opted for either emotivism or subjectivism. Clarke and others opted for rationalism and non-naturalism. In contrast, Catharine Cockburn’s meta-ethics combined Locke’s empiricism with naturalism. She held that moral good is natural good and that natural good is known just as any other matters of natural fact are known: empirically. Cockburn’s position was unusual for its time, and the full originality and appeal of her meta-ethical position have not been fully appreciated.