Proceedings, Eleventh International Conference on Principles of Knowledge Representation and Reasoning (2008) Default Theory of Defeasible Entailment

We suggest a new representation of defeasible entailment and specificity in the framework of default logic. The representation is based on augmenting the underlying classical language with the language of conditionals having its own (monotonic) internal logic. It is shown, in particular, that nonmonotonic inheritance reasoning can be naturally represented in this framework, and generalized to the full classical language. The problem of nonmonotonic, defeasible inference can be seen as the main objective, as well as the main problem of the general theory of nonmonotonic reasoning. An impressive success has been achieved in our understanding of it, in realizing how complex it is, and, most importantly, how many different forms it may have. Many formalism