Relating Defeasible and Default Logic

Abstract

Defeasible reasoning is a simple but efficient approach to nonmonotonic reasoning that has recently attracted considerable interest and that has found various applications. Defeasible logic and its variants are an important family of defeasible reasoning methods. So far no relationship has been established between defeasible logic and mainstream nonmonotonic reasoning approaches.

In this paper we will compare an ambiguity propagating defeasible logic with default logic. In fact the two logics take rather contrary approaches: defeasible logic takes a directly deductive approach, whereas default logic is based on alternative possible world views, called extensions. Computational complexity results suggest that default logics are more expressive than defeasible logics. This paper answers the opposite direction: an ambiguity propagating defeasible logic can be directly embedded into default logic.