  The problem is that default logic does not provide for more specific defaults to override ones that are more general. This principle of specificity has been discussed at length in the literature. Incorporating it in a nonmonotonic logic can complicate the theory considerably; see, for instance,  Asher &amp; Morreau 1991  and  Horty 1994.  And, as  Elkan 1995  points out, the Qualification Problem raises computational issues. 