Simone de Beauvoir
One is not born, but rather becomes, a woman.
Misconceptions
Beauvoir is only Sartre's disciple.
Her texts show a dialogue, not a copy. She takes up the vocabulary of Being and Nothingness and places herself within "existentialist morality". But she writes that Sartre insisted above all on the abortive aspect of the human adventure, and opens the perspective of an ethics only in the last pages: that ethics is what she develops in The Ethics of Ambiguity. There she argues that failure is not surpassed but "assumed", and that freedom, though given at the start, must also be willed to become moral. Finally, the Other applied to the condition of women is her own subject. Who influenced whom, our texts do not settle, and we do not use biographical facts, which lie outside our corpus.
"One is not born a woman, one becomes one" means that the body or sex do not exist, and that everything is a matter of choice.
She speaks of "the human female" and writes that "the division of the sexes is a biological given". What she rejects is destiny: no biological destiny defines the social figure of "woman". And it is not an individual choice: the becoming goes through "the mediation of another", and so-called feminine passivity is "a destiny imposed by teachers and by society". The full discussion of biology (volume I) is not in our corpus.
"One is not born a woman, one becomes one" is the first sentence of The Second Sex.
The book opens on hesitation: "I hesitated a long time before writing a book on woman". The famous line opens volume II, Part One, chapter "Childhood", which begins by explaining what it means. And the translation matters: H. M. Parshley (1953) writes "becomes a woman", Borde and Malovany-Chevallier (2009) "becomes, woman", closer to the French, with no article.