On Rational Jurisprudence: A Problem in Bayesian Confirmation Theory

Abstract

This paper is concerned with the epistemic question of confirming a hypothesis -- the guilt of a defendant -- by way of testimony heard by a juror over the course of an American-style criminal trial. In it, I attempt to settle a dispute between two strands of the legal community over the issue of whether the methods of Bayesian rationality are incompatible with jurisprudential principles such as the Presumption of Innocence. To this end, I prove a representation theorem that shows that so long as a juror would not convict the defendant having heard no testimony (the Presumption of Innocence) but would convict upon hearing some collection of testimony (Willingness to Convict), then this juror's disposition to convict the defendant is representable as the disposition of a Bayesian threshold juror in Posner's sense. This result indicates that relevant notion of a Bayesian threshold juror is insufficiently specified to render this debate a substantive one.