Modal Default Reasoning

Abstract

The aim of my paper is, to provide a simple version of default reasoning which can be hosted in modal logics. The default logic should be capable to represent generic sentences of natural language, but also sentences where explicit reference to gem "normal" objects is made. I will not be concerned with nonmonotonic instanciations of generic sentences, though. I maintain that speakers' defeasible inferences about assumedly normal objects take place at a different level than the representation of ass knowledge about normal objects. I will first list a number of desirable properties which the target formalism should have, and which were reason to turn down other existing approaches. I will next present my answer to these needs, Modal Default Logic (MDL). A final discussion will conclude the paper.