This chapter turns to recent efforts within anthropology and sociology to challenge traditional assumptions regarding purposeful action and shared understanding. A point of departure for the challenge is the idea that commonsense notions of planning are not inadequate versions of scientific models of action, but rather are resources for people's practical deliberations about action. As projective and retrospective accounts of action, plans are themselves located in the larger context of some ongoing practical activity. And as commonsense notions about the structure of that activity, plans are part of the subject matter to be investigated in a study of purposeful action, not something to be improved on or transformed into axiomatic theories of action.

The premise that practical reasoning about action is properly part of the subject matter of social studies is due to the emergence of a branch of sociology named ethnomethodology. This chapter describes the inversion of traditional social theory recommended by ethnomethodology and the implications of that inversion for the prowler of purposeful action and shared understanding.