The article examines the work of the French social philosopher and feminist Jenny P. d'Héricourt, who, in the mid-nineteenth century, debated the writings of contemporary `master-thinkers' such as Auguste Comte, Pierre-Joseph Proudhon and Jules Michelet. Usually ranged exclusively as a contribution to feminist thought, d'Héricourt's writing has also to be understood as a contribution to the conceptual outlines and defining questions of emerging sociology. The stated objective of her main work, La femme affranchie , was not to explain society but to claim equality for women. However, it was precisely her critique of contemporary theories of sexual difference and gender inequality that led d'Héricourt into the territory of sociological thinking — the very same territory her opponents had left by devoting themselves to the creation of a dualistic and asymmetrical concept of gender relations which relied upon women's supposed adversity towards modernity. In her effort to render women's role as agents of modernization visible, d'Héricourt developed, albeit in fragments, a theorem of social integration in modern society that anticipates Émile Durkheim's concept of organic solidarity.