Daniel Carey examines afresh the fundamental debate within the Enlightenment about human diversity. Three central figures - Locke, Shaftesbury, and Hutcheson - questioned whether human nature was fragmented by diverse and incommensurable customs and beliefs or unified by shared moral and religious principles. Locke's critique of innate ideas initiated the argument, claiming that no consensus existed in the world about morality or God's existence. Testimony of human difference established this point. His position was disputed by the third Earl of Shaftesbury who reinstated a Stoic account of mankind as inspired by common ethical convictions and an impulse toward the divine. Hutcheson attempted a difficult synthesis of these two opposing figures, respecting Locke's critique while articulating a moral sense that structured human nature. Daniel Carey concludes with an investigation of the relationship between these arguments and contemporary theories, and shows that current conflicting positions reflect long-standing differences that first emerged during the Enlightenment.