Tech Reports

ULCS-02-006

Added Value: Using Argumentation Frameworks for Reasoning about Problems in Ethics

Trevor J. M. Bench-Capon

Abstract

In this paper I introduce the notion of Value-Based Argumentation Frameworks (VAF). I start from a standard notion of argumentation frameworks which has been widely used to analyse logics for defeasible argument, and extend it so as to make defeat dependent on the relative importance of the values the arguments advance or protect. The idea is to re-introduce an element which has been abstracted away in standard argumentation frameworks, and which can be used to ground a rational choice between alternatives which are equally tenable from the more abstract point of view.

The key result of this paper is to show that in a VAF it may be possible to force rational acceptance of particular arguments within the VAF, irrespective of how the values are ranked. Such arguments can be seen as objectively acceptable. In addition to the definition of VAFs, and exploration of their properties, particularly for the special, but rather common, case where there are precisely two values involved, the paper gives a detailed analysis of a well-known moral dispute in terms of a VAF, and presents some heuristics for extending a given VAF to change the status of particular arguments.

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