Background knowledge as used by ethnomethodologists refers to commonsense reasoning. Members of society, and sociologists, use background knowledge of culture and social structure as an unstated source of guidance in their reasoning.
Commonsense reasoning is also referred to as mundane reasoning. Commonsense reasoning is a term used by ethnomethodologists, derived from Alfred Schutz (1899-1959), referring to the practical or everyday reasoning used by members of society to create and sustain a sense of social reality as being objective, factual, predictable and external to themselves.
Since the objectivity of the world as a practical accomplishment is the focus of ethnomethodology this kind of reasoning is a primary topic of investigation.
Background knowledge is also information that is needed to understand a situation or problem.