The definition of the situation is a fundamental concept in symbolic interactionism advanced by the American sociologist W. I. Thomas. It is a kind of collective agreement between people on the characteristics of a situation, and from there, how to appropriately react and fit into it. Establishing a definition of the situation requires that the participants agree on both the frame of the interaction (its social context and expectations), and on their identities (the person they will treat each other as being for a given situation).