A Default-logic Paradigm for Legal Fact-finding

Unlike research in linguistics and artificial intelligence, legal research has not used advances in logical theory very effectively. This article uses default logic to develop a paradigm for analyzing the reasoning behind legal fact-finding. The article provides a formal model that integrates legal rules and policies with the evaluation of both expert and nonexpert evidence—whether the fact-finding occurs in courts or administrative agencies, and whether in domestic, foreign, or international legal systems. This paradigm can standardize the representation of fact-finding reasoning, guide empirical research into the dynamics of such reasoning, and help prepare such representations and research results for automation through artificial intelligence software. This new model therefore has the potential to transform legal practice and legal education, as well as legal theory. CITATION: Vern R. Walker, A Default-Logic Paradigm for Legal Fact-Finding, 47 Jurimetrics J. 193–243 (2007). Legal scholarship and practice have made too little use of logical theory, and as a result are making too little progress in understanding the formal structure of legal fact-finding, in developing effective methods of searching legal information, and in automating legal reasoning through artificial intelligence (AI). Although legal theorists have long acknowledged the relevance of traditional *Professor of Law, Hofstra University. The author is grateful for the financial support provided by a research grant from Hofstra University and for the comments on the article by the peer reviewers and by Matthew Buschi. 1. Logical theory studies those patterns of reasoning that ought to be persuasive to a reasonable person seeking knowledge. Logic therefore studies reasonable inference, even when it is performed by artificial agents. Logical research is distinct from research into the patterns of reasoning that are in fact persuasive to human beings—research in such fields as psychology, rhetoric, and cognitive science. See, e.g., DOUGLAS WALTON, LEGAL ARGUMENTATION AND EVIDENCE 347 (2002) (contrasting logical uses of argument with psychological or rhetorical uses).