Discourse Models and Language Comprehension

Higher o rder s t r u c t u r e s such as ndiscourseH a n e "intent'ionfi must be included i n any complete t h e o r y of language u n d e r s t a n d i n g . This paper coEpares two approaches t o modeling discourse, The first centers on the c o n c e ~ t of a wdiscourse grammarn which d e f i n e s the set of likely (i.e. easily understood) d l scourse structures, A second approach is a tldemand process ingtr model in which u t t k r a n c e s create demands on both the speaker and the h e a r e r . Res.ponses t o these demands are based o n t h e i r r e l a t i v e vimportancen. bhe length of time they have been a r o u n d , and conditions attached to each demand. The flow of responses provides a n o t h e r l e v e l of e x p l a n a t i o n f o r t h e discourse s t r u e ture. These two approaches are d i s c u s s e d in terms of f l e x i b i l i t y , efficiency, and of t h e i r role i n a more complete t h e o r y of discourse u n d e r s t a n d i n g , As has been s a i d many times, understanding a n y t h i n g a problenr, an acticn, a word demands some knowledge of t h e context fn which it appears. Certainly this is t r u e of language, uhere an utterance s meaning may depend upon who the speaker is, when he i s ta lk ing , what has j u s t been sa id , who the l i s t e n e r s are, what the Durpose of the conversation is, and so on . I t i s reasonable t o d e f i n e language understanding as the process of applying contextual knowledge to a sound (or s t r i n g of symbols) to produce a change i n t h a t c o n t e x t . Successful language undkrstanding scaurs whenever the changes i n t h e hearer s c o n t e x t (model of t h e wor ld ) coincides w i t h changes t h e speaker i n t e n d e d . O f course, s t a t i n g a problem i n a d i f f e r e n t way does n o t solveit, I n s t e a d it suggests a series o f s u b s i d i a r y q u e s t f o n s