The Decisional Nature of Probability and Plausibility Assessments in Juridical Evidence and Proof

Abstract The quantification of uncertainty is a key topic in different theories and accounts of the legal process, ranging from probabilism to explanationism. These accounts invoke probability to various extents. For legal probabilism, probability is the single core concept, whereas other accounts, such as the relative plausibility theory, give it a more limited role, as one consideration among others. At the same time, controversies persist about the nature of probability and the value it may add to the understanding of the broad range of aspects that characterise the legal process. These controversies arise, in part, from the fact that probability itself is the object of confusing debates in many scientific disciplines. In view of these intricacies, this paper argues that the critical analysis and clarification of how to understand and use probability meaningfully remains a topic worthy of investigation across different theoretical perspectives. The first part of this paper critically examines a selection of persisting misconceptions about probability and objections against its use, based on discussions presented in recent evidence law literature. Part II of this paper will blend this discussion with a particular view of probability, interpreted as a personal decision, rarely acknowledged in legal literature. Using a multidisciplinary perspective and a thorough review of historical sources, we illustrate and discuss how the understanding of probability assertion as a decision promotes transparency, honesty, accountability and justifiability. This decisional perspective is further developed and discussed in Part III to show that its logical ingredients underpin key concepts of different theoretical accounts, in particular the assertion of degrees of belief, assessments of relative plausibility and verdicts about ultimate issues at trial. Overall, the paper makes the point that the isolated debates over probability, legal probabilism and reasoning under uncertainty misconceive the primary problem of the legal process, which is decision-making under uncertainty. The proposed decisional perspective clarifies these issues both analytically and descriptively, and resolves divergencies between ostensibly competing concepts such as probability and relative plausibility.