Philosopher Judith Butler's 1990 work, Gender Trouble, shook the foundations of feminist theory and changed the conversation about gender. While many thinkers already accepted that "gender" was a category constructed by society rather than defined by one's genitalia, Butler went further and argued that gender is performative - it exists only in the acts that express it. Society determines that wearing makeup is "feminine" - but some men wear makeup. Are they "women"?
Even as recently as the 1920s the historical lack of great female writers was often considered as evidence of women's inferiority. Virginia Woolf disagreed. In her 1929 essay A Room of One's Own, she argues that creativity is impossible without privacy and freedom from financial worries - and that throughout history women have had neither. As a result, no tradition of great female writing existed to inspire women. Woolf's focus on the everyday suppression of women was a turning point.