Britz, KVarzinczak, I2013-06-182013-06-182013-01Britz, K and Varzinczak, I. 2013. Defeasible modalities. In: Fourteenth conference on Theoretical Aspects of Rationality and Knowledge (TARK), Chennai, India, 7-9 January 2013http://www.cair.za.net/sites/default/files/outputs/TARK-DefModalities.pdfhttp://hdl.handle.net/10204/6801Fourteenth conference on Theoretical Aspects of Rationality and Knowledge (TARK), Chennai, India, 7-9 January 2013. Published in Centre for Artificial Intelligence ResearchNonmonotonic logics are usually characterized by the presence of some notion of `conditional' that fails monotonicity. Research on nonmonotonic logics is therefore largely concerned with the defeasibility of argument forms and the associated normality (or abnormality) of its constituents. In contrast, defeasible modes of inference aim to formalize the defeasible aspects of modal notions such as actions, obligations and knowledge. In this work we enrich the standard possible worlds semantics with a preference ordering on worlds in Kripke models. The resulting family of modal logics allow for the elegant expression of defeasible modalities. We also propose a tableau calculus which is sound and complete with respect to our preferential semantics.enKnowledge representation and reasoningModal logicPreferential semanticsDefeasible modes of inferenceConference PresentationBritz, K., & Varzinczak, I. (2013). Defeasible modalities. Centre for Artificial Intelligence Research. http://hdl.handle.net/10204/6801Britz, K, and I Varzinczak. "Defeasible modalities." (2013): http://hdl.handle.net/10204/6801Britz K, Varzinczak I, Defeasible modalities; Centre for Artificial Intelligence Research; 2013. http://hdl.handle.net/10204/6801 .TY - Conference Presentation AU - Britz, K AU - Varzinczak, I AB - Nonmonotonic logics are usually characterized by the presence of some notion of `conditional' that fails monotonicity. Research on nonmonotonic logics is therefore largely concerned with the defeasibility of argument forms and the associated normality (or abnormality) of its constituents. In contrast, defeasible modes of inference aim to formalize the defeasible aspects of modal notions such as actions, obligations and knowledge. In this work we enrich the standard possible worlds semantics with a preference ordering on worlds in Kripke models. The resulting family of modal logics allow for the elegant expression of defeasible modalities. We also propose a tableau calculus which is sound and complete with respect to our preferential semantics. DA - 2013-01 DB - ResearchSpace DP - CSIR KW - Knowledge representation and reasoning KW - Modal logic KW - Preferential semantics KW - Defeasible modes of inference LK - https://researchspace.csir.co.za PY - 2013 T1 - Defeasible modalities TI - Defeasible modalities UR - http://hdl.handle.net/10204/6801 ER -