Judith Butler (b. 1956) is a professor at the European Graduate School in Saas-Fee, Switzerland and Maxine Elliot Professor in the Departments of Rhetoric and Comparative Literature at the University of California, Berkeley. She is the post-feminist academic who wrote Gender Trouble in 1990 and Bodies That Matter in 1994. Both books describe what later came to be known as queer theory. One of Butler's most significant contributions to critical theory is her performative model of gender, in which the categories "male" and "female" are understood as a repetition of acts instead of natural or inevitable absolutes. Butler also argued that the feminist movement cannot use or rely on a specific immutable definition of woman, and that to do so is imperialistic and counterproductive in that it perpetuates sexism. She also examines the ways that race, gender, sexual orientation, and other identities conflict and support each other.