CrimProf Blog

Editor: Kevin Cole
Univ. of San Diego School of Law

Tuesday, October 10, 2017

Allen on Burdens of Persuasion

This brief paper presented at a celebration of the career of Michael Risinger, briefly reviews why the relative plausibility theory is to date the best explanation of juridical proof and the limits of its chief competitor, a probabilistic explanation. It is true that the legal system is structured to generate the most probable outcome as the verdict in cases; nonetheless, the conclusion of the most plausible (and thus most probable) outcome is achieved through plausible reasoning, not probabilistic reasoning, and virtually the entire procedural context supports, indeed forces the parties to pursue, this approach. A recent competitor to relative plausibility has been advanced in the form of fuzzy set theory that purportedly dissolves the “conjunction paradox,” which is taken as evidence of the inadequacies of the relative plausibility theory. This paper demonstrates that the purported intimate connection between the conjunction paradox and relative plausibility does not exist.
In part this is because the so-called “conjunction paradox” is a feature of the world rather than our thinking about the world, and any explanation of juridical proof must explain this feature of the world to have any chance of success. The apparent resolution of this paradox by fuzzy theorizing thus either must rest on the view that how we think about the world can change how the world behaves, which is unlikely, or on mistakes in the application of fuzzy sets and fuzzy logic. The latter is shown to be the case. Among other difficulties, the argument that fuzzy theorizing eliminates the conjunction paradox is shown to make at least two fundamental mistakes of mathematical logic. First, it confuses a set theoretic definition of the intersection of sets with a probabilistic measure of the probability of events occurring. Second, it confuses the elements of sets with the sets themselves. Fuzzy sets and logic are thus eliminated as competitors to the relative plausibility theory. In passing, it is pointed out that recent arguments about other non-standard methods of evaluating evidence like possibility theory make analogous mistakes of mathematical logic, and thus also are not competitors to supplant relative plausibility as the best explanation of juridical proof.

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