[Woman] is simply what man decrees; thus she is called "the sex," by which is meant that she appears essentially to the male as a sexual being. For him she is sex -- absolute sex, no less. She is defined and differentiated with reference to man and not he with reference to her; she is incidental, the inessential as opposed to the essential. He is the Subject, he is the Absolute -- she is the Other.
Simone de Beauvoir, The Second Sex
feminism, gender, philosophy