One of the central concerns of a theory of pra~atics is to explain what actions language users per fo rm by making u t t e r a n c e s . Th is concern i s a lso r e l e v a n t to the d e s i g n e r s o f c o n v e r s a t i o n a l language unde rs tand ing systems, e s p e c i a l l y those i n tended to coope ra te w i t h a user in the e x e c u t i o n o f some t ask ( e . g . , t he Computer C o n s u l t a n t t ask d iscussed in Walker [1978]).