Commonsense entailment: A modal theory of nonmonotonic reasoning

Abstract

In this paper, we use the Stalnaker-Lewis semantics for conditional logic to construct a truth conditional semantics for generic sentences. The resulting notion of logical entailment captures intuitively valid argument forms involving generics. A dynamic semantics is built on top of the truth conditional one, and the resulting inference notion captures nonmonotonic argument patterns familiar from the artificial intelligence literature. The theory developed here extends that of Asher and Morreau (1991). That theory enables specific information to prevail over more general information by using techniques familiar from prioritized circumscription; this theory uses a constraint on modal frames to achieve the same effect.

We would like to thank Michel Bras, Greg Carlson, Peter Gardenfors, Matt Ginsberg, Jeff Horty, Bob Stalnaker, Rich Thomason, and Frank Veltman for helpful conversations. This reasearch was supported by the ESPRIT Basic Research Action 3175, DYANA, and by Sonderforschungsbereich 340.