On the Comparison of Theories: Preferring the Most Specific Explanation

Abstract

Default reasoning is reasoning with generalised knowledge which we want to use if there is no more specific knowledge also applicable . This paper presents a formal, model-theoretic characterisation of default reasoning. Defaults are treated as possible hypotheses in a "scientific" theory to explain the results. One of the problems with systems that reason with defaults occurs when two answers can be produced, and one is preferred. In terms of our default logic, we define a semantic characterisation of the notion of the more specific theory. This overcomes many of the problems which motivated non-normal defaults, and provides a semantics for correct inheritance in inheritance systems, where we want choose the result supported by the most specific knowledge. We also show how to produce a general computational mechanism in terms of normal first order predicate calculus deduction systems.