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

A Scenario Approach to the Simonshaven Case

“…Third, some adherents of the scenario approach, and more widely of "explanationist" approaches (Allen & Pardo, 2019), have serious doubts whether formal, let alone quantitative, analyses of criminal cases as a whole can offer more valid (in the social-scientific meaning of the word) decisions than the informal and qualitative analyses that explanationist approaches offer.…”

“…An important difference between the scenario approach and other "explanationist" theories such as Thagard's (2000) and Allen and Pardo's (2019) is the central role that scenarios play. The story model of Pennington and Hastie (1993) on how people actually reason with stories in everyday life was further developed by Wagenaar, Van Koppen, and Crombag (1993), who presented it both as a descriptive and a normative theory.…”

Civil liability and the 50%+ standard of proof

“…The otherwise equal treatment of plaintiff and defendant is often justified on the grounds that, once an action has been initiated, the stakes might be regarded as equivalent for the two parties. Put differently, the two kinds of error that can be made in a civil trial—an erroneous finding in favour of the plaintiff and an erroneous finding in favour of the defendant—might be regarded as being equally costly (see, for instance, Allen, 2014: 199–200: Allen and Pardo, 2019: 9–10; Ball, 1961: 815–816; Brook, 1985: 297; Kitai, 2003: section II; In re Winship 397 U.S 358 [1970] at 371; for discussion, see Nance, 2016: section 2.2.1). Suppose a plaintiff sues a defendant for £100,000.…”

“…Consider again the claim, canvassed in the last section, that deliberation in a civil trial is largely a matter of comparing the plausibility of competing narratives. This thought lies at the heart of the relative plausibility theory of legal proof defended in a number of papers by Ronald Allen and Michael Pardo (see, for instance, Allen, 1986, 1994, 2008; Allen and Pardo, 2019; Pardo, 2019; Pardo and Allen, 2008). 16 The way I will develop this approach here owes much to Allen and Pardo’s work—though, as will emerge, there are some significant differences.…”

“…If, on the other hand, plausibility is independent of probability—is a matter of ‘telling a good story’ no matter how unlikely—then this is no basis for legal adjudication (Nance, 2016: section 2.3.2; see also Schwartz and Sober, 2017: section IIC2). As should be clear from the foregoing discussion, Allen and Pardo’s response to this is to reject the second horn of the dilemma and to tie plausibility and probability closer together, while attempting to resist the charge that the relative plausibility theory would then reduce to the 50%+ interpretation (Allen and Pardo, 2019: section IIA). 19…”