Butler's 1990 work 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 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"? Following Butler's argument, they are if they say they are. Butler frees gender from the age-old binary construct and demonstrates that it is indefinable, at least by society. Her approach gives each of us the power to define our gender.