Lexical Marking And The Recovery Of Discourse Structure

In the theory presented here, discourse relations are equated with coherence relations. The relata are taken to be sets of events or entities introduced into the discourse, as in SDRT (Asher, 1993). Our empirical studies of commentary, narrative and news texts have shown that coherence relations are frequently signaled syntactically or semantically rather than lexically. In a full natural language understanding design, this much discourse structure can be recognized computationally. However, there remain discourses in which the coherence relations are unmarked even by syntax, tense or aspect. Some of these relations cannot be recognized computationally because they require extensive world knowledge. Ultimately any relation between events or objects which is common knowledge among discourse participants can form the basis for a felicitous request for an unmarked coherence inference. In order to recognize all coherence relations, a computational system needs full world knowledge.