A General Scheme for Formalizing Defaults Usingthe Predicate ab(I,S)

In common sense reasoning two typical types of defaults are encoun- tered. One is of the form "All birds can fly except b1, b2,…, and bm(m>1)" , and the other "All birds can fly, but there exist exceptiona" . The first type of defaults is readily formalized but the other, as some researchers have noticed, is difficult to deal witb. This paper establisbes a geaeral scheme for formalising defaults of the two typea, the key to which is the introduction of a two-argument predicate ab(I,S) to represent exception…