Genre-dependent interaction of coherence and lexical cohesion in written discourse

We investigate the interaction between coherence and lexical cohesion in expository and persuasive texts using seven encyclopedia texts and seven fundraising letters. We describe genre structure in terms of genre-specific moves and coherence structure with Rhetorical Structure Theory. For lexical cohesion, we identify repetitions, systematic semantic relations and collocations across discourse units, modeled as weighted multigraphs. By comparing the prominence of discourse units in the coherence structure with the centrality in the lexical cohesion structure in the two genres, we show that lexical cohesion is closely aligned with coherence in the expository texts, but not in the persuasive texts.