This article provides a developmental description of the language used by an academic discourse community. Casual conversations of six post-graduate students, native speakers of English, were recorded in the Applied Linguistics common room in Edinburgh University throughout the 1991-2 course. The central hypothesis was that as common knowledge of the course and shared interpersonal knowledge increase over time, there is an increase in implicit language heavily dependent on the context for its meaning. The grammatical analysis shows that the increase in knowledge over time is associated with an increase in implicit reference, but that topic is also a major influence on the form of reference. The language of course topics is more implicit than that of non-course topics. Course topics have a higher density of non-anaphoric non-modified definite referring expressions with specific referents in the assumed background knowledge. The findings may help to equip EAP students to interact better socially with their colleagues.