This paper explores two questions central to understanding the nature of formulaic sequences: (1) What are they for? and (2) What determines how many there are? The “Communicative Impact” model draws into a single account how language is shaped by cognitive processing on the one hand and socio-interactional function on the other: Formulaic sequences play a range of coordinated roles in neutralizing unanticipated perturbations in the cognitive management of language, so the speaker's socio-interactional goals can still be achieved. One role (...) involves compensatory actions to sustain fluency. However, these actions are themselves context-sensitive, so the balance of types of formulaic sequence will vary according to situation. The model applies equally to temporary cognitive pressure and chronic problems such as dementia and limited linguistic competency in a foreign language. (shrink)