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

摘要

In common sense reasoning two typical types of defaults are encoun- tered. One is of the form "All birds can fly except b_1, b_2,.. ., and b_m (m ≥ 1)", and the other "All birds can fly, but there exist exceptions". The first type of defaults is readily formalized but the other, as some researchers have noticed, is difficult to deal with. This paper establishes a general scheme for formalizing defaults of the two types, the key to which is the introduction of a two-argument predicate ab(I, S) to represent exceptional objects.