Relative Plausibility and its Critics

Abstract

Within legal scholarship there is a tendency to use (perhaps overuse) “paradigm shift” in ways far removed from the process famously described by Thomas Kuhn. Within the field of evidence, however, a phenomenon very similar to a paradigm shift, in the Kuhnian sense, is occurring. Although not on the scale of the transformation from Newtonian to Einsteinian physics or other tectonic shifts in science, the best understanding of juridical proof is shifting from probabilism to explanationism. For literally hundreds of years, proof at trial was assumed to be probabilistic. This assumption was given sustained scholarly attention and support beginning with the 1968 publication of John Kaplan’s path-breaking article that generated a rich literature explaining virtually all aspects of juridical proof as probabilistic, from the basic nature of relevancy through the processing of information to the final decision about the facts. Although probabilism quickly became the dominant paradigm, some analytical difficulties were detected quite early (“anomalies” or “irritants” in the words of Kuhn), beginning with L. Jonathan Cohen’s demonstration of certain proof paradoxes. These were extended by Ronald Allen, who also demonstrated the incompatibility of Bayesian reasoning with trials and proposed an analytical alternative. Again a complex literature ensued with the defenders of the dominant paradigm attempting to explain away the anomalies or to shield the probabilistic paradigm from their potentially corrosive effects (in what in fact on a very small scale is precisely what Kuhn explained and predicted with respect to paradigm shifts in science). Over the last two decades, these anomalies have become too irritating to ignore, and the strengths of the competing paradigm involving explanatory inferences (referred to as the relative plausibility theory) have become too persuasive to dismiss. Thus the paradigm shift that the field is now experiencing.

We provide here a summary of the relative plausibility theory and its improvement on the probabilistic paradigm. As Kuhn noted, not everybody gets on board when paradigms shift; there are holdouts, dissenters, and objectors. Three major efforts to demonstrate the inadequacies of relative plausibility have recently been published. We analyze them here to demonstrate that their objections are either misplaced or unavailing, leaving relative plausibility as the best explanation of juridical proof. It is interesting to note that two of the three critiques that we discuss actually agree with the inadequacies of the probabilistic paradigm (they provide alternatives). The third concedes that explanationism may provide a better overall account of juridical proof but tries to resuscitate a probabilistic interpretation of burdens of proof in light of one particular analytical difficulty (i.e., the conjunction problem, which arises from the fact that proof burdens apply to the individual elements of crimes, civil claims, and defenses). In analyzing the alternative positions proposed by our critics, we demonstrate that their accounts each fail to provide a better explanation than relative plausibility.

Keywords: evidence, juridical proof, probability, plausibility, explanations, standards of proof, inference to the best explanation, conjunction problem