Coherence structure and lexical cohesion in expository and persuasive texts

This paper reports preliminary results. from an ongoing project investigating the alignment between coherence structure and lexical cohesion in thematically organized expository texts (encyclopedia entries) and intentionally structured persuasive texts (fundraising letters) at the global level of discourse organization. A genre-specific description of the coherence structure is achieved by mapping genre-specific moves onto the top levels of Rhetorical Structure Theory (RST) trees. Networks of lexical cohesion are formed by word repetition, systematic semantic relations (e.g. hyponymy, meronymy, and synonymy) and collocation relations between lexical items. By comparing the centrality of text parts in the coherence and cohesion structures, we show that coherence is more closely aligned with lexical cohesion in the expository texts than in the persuasive texts.