Ruth Barcan Marcus was born in New York City to a secular European Jewish family. Her father was a printer and contributing writer at the Jewish Daily Forward, as well as a member of the Socialist Party and the Workman’s Circle. Ruth and her sisters attended the Workman’s Circle’s Yiddish-language neighborhood schools in the afternoons. She went to public school, including Herman Ridder Junior High School for intellectually gifted students, and Evander Childs High School. She earned a B.A. in mathematics and philosophy from New York University in 1941, graduating Phi Beta Kappa, and a Ph.D. in philosophy from Yale University in 1946. During her college years, she edited a literary magazine, ran the mathematics and philosophy societies, and was an outstanding fencer. In 1942, she married Jules A. Marcus, a physicist, with whom she had four children. Ruth Barcan Marcus held several fellowships and visiting positions. She was appointed head of the Philosophy Department at the University of Illinois at Chicago in 1964. She also was a professor at Northwestern University and then at Yale University. She retired as Reuben Post Halleck Professor at Yale in 1992. Early in her career, she proposed the Barcan formula in quantified modal logic. She published papers in the philosophy of logic and language, epistemology, and ethics, and several books, including a collection of her essays, Modalities (1993).