Plausibility measures and default reasoning: an overview

Nir Friedman*, Joseph Y. Halpern

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

4 Scopus citations


We introduce a new approach to modeling uncertainty based on plausibility measures. This approach is easily seen to generalize other approaches to modeling uncertainty, such as probability measures, belief functions, and possibility measures. We then consider one application of plausibility measures: default reasoning. In recent years, a number of different semantics for defaults have been proposed, such as preferential structures, possibilistic structures, and K-rankings, that have been shown to be characterized by the same set of axioms, known as the KLM properties. While this was viewed as a surprise, we show here that it is almost inevitable. In the framework of plausibility measures, we can give a necessary condition for the KLM axioms to be sound, and an additional condition necessary and sufficient to ensure that the KLM axioms are complete. This additional condition is so weak that it is almost always met whenever the axioms are sound. In particular, it is easily seen to hold for all the proposals made in the literature. Finally, we show that plausibility measures provide an appropriate basis for examining first-order default logics.

Original languageAmerican English
Title of host publicationProceedings - Symposium on Logic in Computer Science
Number of pages6
ISBN (Print)0780357701
StatePublished - 1999
EventProceedings of the 1999 14th Symposium on Logic in Computer Science, LICS'99 - Trento, Italy
Duration: 2 Jul 19995 Jul 1999


ConferenceProceedings of the 1999 14th Symposium on Logic in Computer Science, LICS'99
CityTrento, Italy


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