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On the graded acceptability of arguments in abstract and instantiated argumentation

Research output: Contribution to journalArticle

Davide Grossi, Sanjay Modgil

Original languageEnglish
Pages (from-to)138-173
Number of pages36
JournalARTIFICIAL INTELLIGENCE
Volume275
Early online date10 May 2019
DOIs
Accepted/In press3 May 2019
E-pub ahead of print10 May 2019
Published1 Oct 2019

King's Authors

Abstract

The paper develops a formal theory of the degree of justification of arguments, which relies solely on the structure of an argumentation framework, and which can be successfully interfaced with approaches to instantiated argumentation. The theory is developed in three steps. First, the paper introduces a graded generalization of the two key notions underpinning Dung's semantics: self-defense and conflict-freeness. This leads to a natural generalization of Dung's semantics, whereby standard extensions are weakened or strengthened depending on the level of self-defense and conflict-freeness they meet. The paper investigates the fixpoint theory of these semantics, establishing existence results for them. Second, the paper shows how graded semantics readily provide an approach to argument rankings, offering a novel contribution to the recently growing research programme on ranking-based semantics. Third, this novel approach to argument ranking is applied and studied in the context of instantiated argumentation frameworks, and in so doing is shown to account for a simple form of accrual of arguments within the Dung paradigm. Finally, the theory is compared in detail with existing approaches.

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