, Volume 176, Issue 2, pp 243–274 | Cite as

Well-founded semantics for defeasible logic

  • Frederick MaierEmail author
  • Donald Nute


Fixpoint semantics are provided for ambiguity blocking and propagating variants of Nute’s defeasible logic. The semantics are based upon the well-founded semantics for logic programs. It is shown that the logics are sound with respect to their counterpart semantics and complete for locally finite theories. Unlike some other nonmonotonic reasoning formalisms such as Reiter’s default logic, the two defeasible logics are directly skeptical and so reject floating conclusions. For defeasible theories with transitive priorities on defeasible rules, the logics are shown to satisfy versions of Cut and Cautious Monotony. For theories with either conflict sets closed under strict rules or strict rules closed under transposition, a form of Consistency Preservation is shown to hold. The differences between the two logics and other variants of defeasible logic—specifically those presented by Billington, Antoniou, Governatori, and Maher—are discussed.


Defeasible reasoning Nonmonotonic logic Well-founded semantics Ambiguity propagation Floating conclusions Cut Cautious monotony Consistency preservation 


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Copyright information

© Springer Science+Business Media B.V. 2009

Authors and Affiliations

  1. 1.Florida Institute for Human and Machine CognitionPensacolaUSA
  2. 2.Institute for Artificial IntelligenceThe University of GeorgiaAthensUSA

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