The Enlightenment devoted great energies to the definition of gender, so great in fact that some historians have seen this period as a watershed in European culture's attempts to define difference between the sexes. Gender, like the exotic, was an area of difference. It therefore challenged some very strong strands in Enlightenment thought, the strands that emphasised the idea of a universal human nature, and a universal human history, both validated by the possession of a single universal human form of rationality. It was no accident that by the end of the eighteenth century many thinkers such as Mary Wollstonecraft were to equate the denial of rights to slaves and the denial of rights to women. Each destabilised crucial Enlightenment assumptions. Yet in practice as well as in much Enlightenment writing, each was insisted upon. This chapter attempts to understand this contradiction.