A Semantic Decomposition of Defeasible Logics

Abstract

We investigate defeasible logics using a technique which decomposes the semantics of such logics into two parts: a specification of the structure of defeasible reasoning and a semantics for the meta-language in which the specification is written. We show that Nute's Defeasible Logic corresponds to Kunen's semantics, and develop a defeasible logic from the well-founded semantics of Van Gelder, Ross and Schlipf. We also obtain a new defeasible logic which extends an existing language by modifying the specification of Defeasible Logic. Thus our approach is productive in analysing, comparing and designing defeasible logics. Introduction In this paper we start from Nute's Defeasible Logic (Nute, 1987; Nute 1994). This logic has an expressive syntax, a strongly skeptical semantics and a tractable computational behavior. Our interest, in this paper, is to decompose Defeasible Logic into parts, for the analysis of the logic, and also to reassemble it with different parts to create new and dif...