The trouble with standards of proof

Abstract

The “beyond a reasonable doubt” standard of proof, currently used in criminal trials, is notoriously vague and undermotivated. This paper discusses two popular strategies for justifying our choice of a particular precise interpretation of the standard: the “ratio-to-standard strategy” identifies a desired ratio of trial outcomes and then argues that a certain standard is the one that we can expect to produce our desired ratio, while the “utilities-to-standard strategy” identifies utilities for trial outcomes and then argues that a certain standard maximizes expected utility. I argue that both strategies fail on their own terms, by requiring us to perform calculations that we simply cannot perform. No version of either strategy can be performed by jurors or legislators in our actual epistemic position, in which, since we do not know which of the defendants in our trial system are genuinely innocent and which are genuinely guilty, we cannot determine the extent to which our trial system tends to produce evidence that misleadingly incriminates the innocent or misleadingly exonerates the guilty. But we would need to determine this in order to perform the calculations required by any possible version of the ratio-to-standard or utilities-to-standard strategies. I then suggest some empirical reasons to be pessimistic about the evidence produced by our actual trial system. The upshot is that the “beyond a reasonable doubt” standard lacks a clear interpretation and rationale, nor do we have a promising way to identify an alternative. This is the trouble with standards of proof.