Linguistic symbols are conventionalized behavioral expressions that human beings use to manipulate one another’s attention, including everything from words to complex syntactic constructions to narrative genres. Conventionalization is only a distillation of past uses, of course, and so it is of limited help when language users face novel communicative exigencies – which they do on a regular basis since, at some level of detail, each and every communicative event is unique. An essential component of human linguistic competence, therefore, is a speaker’s ability to use her conventionalized linguistic inventory in flexible ways depending on a number of parameters of the communicative context. Perhaps of special importance in this process is the speaker’s assessment of the knowledge and expectations of the listener at the current moment, including a characterization of the nature and degree of their ‘common ground’ (Clark 1996). Effective communication requires that the speaker make an accurate assessment of this common ground and then make appropriate linguistic choices in light of this assessment.