Simone de Beauvoir

The Second Sex (1949) supplied the movement's core idea: "One is not born, but rather becomes, a woman." Using existentialist philosophy, Beauvoir argued that men have defined themselves as the human norm and women as the "Other", so femininity is a situation imposed rather than a nature. Later feminists split over her legacy: some built on it, others objected that she treated motherhood and the female body mainly as obstacles.