A Logical Analysis of Burdens of Proof

The legal concept of burden of proof is notoriously complex and ambiguous. Various kinds of burdens of proof have been distinguished, such as the burden of persuasion, burden of production and tactical burden of proof, and these notions have been described by different scholars in different ways. They have also been linked in various ways with notions like presumptions, standards of proof, and shifts and distributions of burdens of proof. What adds to the complexity is that different legal systems describe and treat the burden of proof in different ways. For instance, in common-law jurisdictions the just-mentioned distinction between three kinds of burden of proof is explicitly made while in civil law systems it usually remains implicit. This paper aims to clarify matters concerning burden of proof from a logical point of view. We take a logical point of view since, although some differences in notions and treatments might reflect legitimate legal differences between jurisdictions, we think that to a large extent the burden of proof is an aspect of rational thinking and therefore subject to a logical analysis. In particular, we claim that the burden of proof can be adequately analysed in terms of logical systems for defeasible argumentation, i.e., logics for fallible (but not fallacious!) reasoning. The grounds for this claim are fourfold. Firstly, since legal proof almost always has an element of uncertainty, we cannot impose a deductive form onto real legal evidential reasoning. Secondly, while this reason still leaves open the use of other approaches, such as story-based or statistical approaches, we think that the notion of argumentation and related notions such as counterargument, rebuttal and dispute, are very natural to legal thinking. Thirdly, (and a special case of the second reason), logics for defeasible argumentation are arguably suitable as a formal underpinning of much work of the influential New Evidence scholars, such as Anderson, Tillers, Twining and Schum (e.g. Anderson et al. 2005, who revived and modernised Wigmore’s famous charting method for making sense of legalevidential problems. (See Prakken 2004 for a defence of the thesis that argument-based logics can be a formal underpinning of this work). Finally, logics for defeasible argumentation have a firm theoretical basis both in philosophy (especially in argumentation theory) and in logic (especially in its applications in artificial