Burden of Persuasion in Argumentation

This paper provides a formal model for the burden of persuasion in dialogues, and in particular, in legal proceedings. The model shows how an allocation of the burden of persuasion may induce single outcomes in context in which the assessment of conflicting argument would, without such an allocation, remain undecided. Our approach is based on a two-stage labelling. The first stage labelling determines whether arguments are accepted, rejected or undecided regardless of the allocation of the burden. The second stage labelling revises the dialectical status of first-stage undecided arguments according to whether the burden of persuasion is on the conclusion of such arguments, or rather on its complements. The labelling is then extended in such a way as to possibly obtain a complete labelling. Our model merges two ideas that have emerged in the debate on the burden of proof: the idea that allocation of the burden of proof enables the decision of conflicts between arguments, and the idea that its satisfaction depends on the dialectical statuses of the concerned arguments. The step further of our approach is to provide a way to resolve conflicts between different burdens (such as when there are two arguments, each attacking a subargument of the other, the conclusions of such subarguments being the object of burdens of persuasion) and to be able to deal with cases in which there is an inversion of the proof.