 What is perhaps the most famous line of The Second Sex, “On ne naît pas femme: on le devient” (1949, 13), translated in 1953 as  “One is not born but becomes a woman” (1953, 267) and in 2010 as “One is not born but becomes woman”, is credited by many as alerting us to the sex-gender distinction. Whether or not Beauvoir understood herself to be inaugurating this distinction, whether or not she followed this distinction to its logical/radical conclusions, or whether or not radical conclusions are justified are currently matters of feminist debate. What is not a matter of dispute is that The Second Sex gave us the vocabulary for analyzing the social constructions of femininity and a method for critiquing these constructions. By not accepting the common sense idea that to be born with female genitalia is to be born a woman this most famous line of The Second Sex pursues the first rule of phenomenology: identify your assumptions, treat them as prejudices and put them aside; do not bring them back into play until and unless they have been validated by experience.