Abstract

We address problems of conflicting evidence--ambiguity--in nonmonotonic reasoning. In particular, we provide a unified framework for studying such ambiguity and for identifying principles that may aid in resolving it. This framework clarifies the issues that underlie particular ambiguity problems. It unifies existing approaches by providing a common description language. And it suggests new solutions by shifting the focus to underlying principles, rather than particular procedures. We analyze three specific examples of ambiguity--in inheritance, temporal reasoning, and counterfactual reasoning--in terms of this unified framework, and provide systems for reasoning about these ambiguities based on the principles of specificity, causation, and similarity of worlds