Representing Explicit Exceptions

Abstract

The structure of the rest of this book requires some explanation. As a consequence of the conclusion of Chapter 3 that legal reasoning is defeasible, some logics for nonmonotonic reasoning were discussed in Chapter 4. However, the discussion was still at a general level; in the next two chapters these logics will be applied to defeasible reasoning in law. The investigations will be based on a distinction between two conceptual methods of dealing with exceptions. The first method, using explicit exception clauses1 to obtain unique answers, will be discussed in this chapter, while the second method, leaving exceptions implicit and preferring the most specific of two conflicting conclusions, is the subject of Chapter 6. However, a complication is that the second method is not merely a way of dealing with exceptions, but also one possible application of more general techniques of reasoning with inconsistent information, which is the second major topic of this book. Therefore, Chapter 6 can not only be regarded as the second chapter on dealing with exceptions, but also as the first chapter on inconsistency handling. Chapters 7 and 8 then continue the discussion of this topic, and in one of the sections of Chapter 10 I return to the application of inconsistency handling to defeasible reasoning, in a general comparison of the two methods of representing exceptions.