On direct and indirect probabilistic reasoning in legal proof

Abstract

In the academic literature three approaches to rational legal proof are investigated, broadly speaking based, respectively on Bayesian statistics, on scenario construction and on argumentation. In this paper these approaches are discussed in light of a distinction between direct and indirect probabilistic reasoning. Direct probabilistic reasoning directly reasons from evidence to hypotheses, while indirect probabilistic reasoning reasons from hypotheses to evidence (and then back to the hypotheses). While statistical and story-based approaches usually model indirect probabilistic reasoning, argumentation-based approaches usually model direct probabilistic reasoning. It has been suggested that all legal probabilistic reasoning should be indirect, but in this paper it is argued that direct probabilistic reasoning has a rational basis and is, moreover, sometimes easier to perform for judges than indirect probabilistic reasoning. Moreover, direct probabilistic reasoning can be analysed in terms of standard probability theory, resulting in an alternative, non-Bayesian use of the terms prior and posterior probability and without the need to estimate unconditional probabilities of the hypotheses.