A Formal Model of Adjudication

This article presents a formal dialogue game for adjudication dialogues. Existing AI & law models of legal dialogues and argumentation-theoretic models of persuasion are extended with a neutral third party, to give a more realistic account of the adjudicator’s role in legal procedures. The main feature of the model is a division into a pleadings phase, where the adversaries plea their case and the adjudicator has a largely mediating role, and a trial phase, where the adjudicator decides the dispute on the basis of the claims, arguments and evidence put forward in the pleadings phase. The model allows for explicit decisions on admissibility of evidence and burden of proof by the adjudicator in the pleadings phase. Adjudication is modelled as putting forward arguments, in particular undercutting and priority arguments, in the trial phase. The model reconciles logical aspects of burden of proof induced by the defeasible nature of arguments with dialogical aspects of burden of proof as something that can be allocated by explicit decisions on legal grounds.