Argument Revision

Understanding the dynamics of argumentation systems is a crucial component in the de-velopment of computational models of argument that are used as representations of belief. To that end, in this paper, we introduce a model of Argument Revision, presented in terms of the contraction and revision of a system of structured argumentation. Argument Revi-sion is influenced by the AGM model of belief revision, but with certain key differences. Firstly, Argument Revision involves modifying the underlying model (system of argumen-tation) from which beliefs are derived, allowing for a finer-grained approach to modifying beliefs. Secondly, the richer structure provided by a system of argumentation permits a determination of minimal change based on quantifiable effects on the system as opposed to qualitative criteria such as entrenchment orderings. Argument Revision does, however, retain a close link to the AGM approach to belief revision. A basic set of postulates for rational revisions and contractions in Argument Revision is proposed; these postulates are influenced by, and capture the spirit of, those found in AGM belief revision. After specifying a determination of minimal change, based on measurable effects on the system, we conclude the paper by going on to show how Argument Revision can be used as a strategic tool by a participant in a multi-agent dialogue, assisting with commitment retraction and dishonesty. In systems of argumentation that contain even small knowledge bases, it is difficult for a dialogue participant to fully assess the impact of seemingly trivial changes to that knowledge base, or other parts of the system; we demonstrate, by means of an example, that Argument Revision solves this problem through a determination of minimal change that is justifiable and intuitive.