relevance theory

"In this conceptual model, the author takes into account the context
of the communication *and the mutual cognitive environment* between
the author and the audience. (That is what the author/speaker thinks
that audience already knows). They then say just enough to communicate
what they intend - relying on the audience to fill in the details that
they did not explicitly communicate." --
http://en.wikipedia.org/wiki/Relevance_theory

(my emphasis)