Game theory has also been used in philosophy. Responding to two papers by W.V.O. Quine from 1960 and 1967, used game theory to develop a philosophical account of convention {norm}. With this, he provided the first analysis of common knowledge and used it to analyze play in coordination games. In addition, he first suggested that it is possible to understand meaning in terms of signaling games. This suggestion has been pursued by several philosophers since Lewis. Edna Ullmann-Margalit (1977) and Bicchieri (2006) developed theories of social norms. They define them as Nash equilibria which arise from transforming a mixed-motive game into a coordination game.