  We  briefly mention three contributions to this area. Building on the fact that the rules governing conversation are exception-ridden, Alex Lascarides and Nicholas Asher have developed techniques for formalizing discourse phenomena based on nonmonotonic logic; see  Asher &amp; Lascarides 1994,  Asher &amp; Lascarides 1997.  Jerry Hobbs and various co-workers look at the inference processes used in discourse as abductive, and propose to formalize abduction as a search for a proof in which certain “low-cost” assumptions may be made which serve as data or additional axioms for the proof.  Hobbs et al. 1993  shows how an impressive range of discourse phenomena can be formalized using this idea. In practice, this abductive account looks rather similar to that of Lascarides and Asher, because it involves deploying axioms about discourse (in the form of Horn clause rules supplemented with weights giving the assumption costs of premises) that in effect are nonmonotonic.