Commonsense Entailment: A Modal Theory of Non-monotonic Reasoning

In this paper, we construct a truth conditional semantics for generic sentences, which treats arbitrarily deep nestings of 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 by exploiting constraints on modal frames alone, without the use of ordering principles on rules, abnormality or "relevance" predicates.