Saturation, nonmonotonic reasoning and the closed-world assumption
Artificial Intelligence
Nonmonotonic reasoning, preferential models and cumulative logics
Artificial Intelligence
Theoretical foundations for non-monotonic reasoning in expert systems
Logics and models of concurrent systems
What does a conditional knowledge base entail?
Artificial Intelligence
General patterns in nonmonotonic reasoning
Handbook of logic in artificial intelligence and logic programming (vol. 3)
Conditional Logics for Default Reasoning and Belief Revision
Conditional Logics for Default Reasoning and Belief Revision
Conditional logics of normality as modal systems
AAAI'90 Proceedings of the eighth National conference on Artificial intelligence - Volume 1
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Our subject is the representation and analysis of simple first-order default statements of ordinary language, such as “normally, birds fly”. There are, among other approaches, two kinds of analysis, both semantic in style. One interprets “normally, birds fly” along the lines of “for every item x in the domain of discourse, the most normal models of “x is a bird” are models of “x flies””. This is the preferential models approach, first outlined by Bossu/Siegel and Shoham, and studied by Kraus, Lehmann, Magidor and others. The other interprets “normally, birds fly” along the lines of “there is an important subset of the birds, all of whose elements fly”. This is the generalized quantifier approach, formulated and developed by the author. The purpose of the present paper is to show how the two approaches may usefully be combined into a single two-stage approach, and how such a combination provides an elegant account of certain problematic examples.