Ruth Barcan Marcus (1921–) was educated at Yale, received a Guggenheim fellowship in 1952, and was a founding chair of the philosophy department at the University of Illinois at Chicago. After working as a professor at Northwestern University, she was Halleck Professor of Philosophy at Yale University from 1973 to 1991. She worked in the formal subjects of quantification theory and modal logic, sometimes in disagreement with W.V.O. Quine (1908–2000).

One of her most striking achievements was an early formulation of the new causal theory of reference, made famous by Hilary Putnam (1926–) and Saul Kripke (1940–). The causal theory of reference held that words for things have a history from the first time someone used a specific word to stand for a specific object or idea. For example, we call apples “apples” because that word was the first at some time, in some specific place, to be used to name the fruit. As proponents of the causal theory of reference put it, apples were baptized “apples.”

Marcus’ ground-breaking journal articles are collected in Modalities: Philosophical Essays (1993). She received the American Philosophical Association Quinn Prize for service to the profession in 2007.