Working Paper – Do Not Cite or Quote without Author’s Written Permission Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning

In modern legal systems, the litigated issues are numerous, the reasoning is complex, and the decision-making processes are highly regulated. Moreover, the decision-making integrates legal rules and policies with expert and non-expert evidence. What is needed is a means of representing, studying, and partially automating such complex legal reasoning. This paper presents a visual framework for modeling that reasoning, based on a many-valued, predicate, default logic. It first presents those elements of the logic model that help visualize the reasoning on the two sides of the rule/evidence interface: rulebased deductions and evidence evaluation. It then explores ways to visualize certain dynamics around that interface. Within a single case, the topics are visualization of evidentiary relevance, of findings based on the evidence, of process decision-making about motions, of policy-based reasoning about rules, and of relevant-factor reasoning generally. The paper then concludes with the topic of visualizing dynamics across multiple cases, and briefly discusses one pathway by which new legal rules might emerge from the factfinding process. The paper therefore presents a visual working environment for people who litigate or decide actual cases, or who study judicial or administrative reasoning, or who teach law. INTRODUCTION In modern legal systems, the litigated issues are numerous, the reasoning is complex, and the decision-making processes are highly regulated. Moreover, the decision-making integrates legal rules and policies with expert and non-expert evidence. What is needed is a means of representing, studying, and partially automating such complex legal reasoning. The goal of this ∗ Professor of Law, Hofstra University School of Law. This paper is based on a presentation at the Conference on Graphic and Visual Representations of Evidence and Inference in Legal Settings, at the Cardozo School of Law in New York City on January 28, 2007. The author is grateful for the research support provided by Hofstra University. Vern R. Walker Page 2 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite paper is to visualize elements of one solution to this problem – a default-logic framework based on a many-valued, predicate, default logic. Details of the logic of this framework have been published elsewhere. The purpose here is to visualize the logical landscape as seen from this default-logic perspective, not to provide a detailed map of that terrain. The paper first identifies the two sides of the “rule/evidence interface,” and then discusses the basic dynamics that occur around that interface. Part I presents visualizations for legal rules and the deductions based on them, as well as for evidence and the reasoning that evaluates it. Part II then discusses five aspects of the dynamics around that interface in a single case: the visualization of evidentiary relevance, of findings based on the evidence, of process decision-making about motions, of policy-based reasoning about rules, and of relevant-factor reasoning generally. Part III introduces the topic of visualizing dynamics across multiple cases, and briefly discusses one pathway by which new legal rules might emerge from the factfinding process. I. VISUALIZING THE TWO SIDES OF THE INTERFACE This part of the paper introduces the logic model for the two sides of the rule/evidence interface. It first visualizes the “rules side” of the interface, and models the reasoning that consists of deductions based on legal rules. The second section visualizes the “evidence side” of 1 Vern R. Walker, A Default-Logic Paradigm for Legal Factfinding, 47 JURIMETRICS: THE JOURNAL OF LAW, SCIENCE, & TECHNOLOGY [] (forthcoming, Spring 2007) (hereinafter “Default-Logic Paradigm”); Vern R. Walker, Challenges for a Representational Logic of Legal Factfinding, in ARGUMENTATION, LOGIC, AND LAW [] (forthcoming, 2007) (hereinafter “Challenges”). Vern R. Walker Page 3 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite the interface, and models the reasoning involved in evaluating evidence. The extended examples throughout this part are drawn from the federal compensation system established by the National Childhood Vaccine Injury Act (the “Vaccine Act”). A. VISUALIZING RULE-BASED DEDUCTIONS It is common to model legal rules as conditional propositions, and to visualize a set of related legal rules as having a tree-like structure. The “implication tree” shown in Figure 1 is a drawing of the high-level rules that govern compensation awards under the Vaccine Act. The ultimate issue to be determined is whether compensation should be awarded under the National Vaccine Injury Compensation Program (the proposition at the top of the tree). The conjunction below this conclusion shows that compensation should be awarded if several conditions are met: first, that “the person who suffered the injury or who died received a vaccine set forth in the 2 42 U.S.C. §§ 300aa-10 et seq. 3 See, e.g., Scott Brewer, Exemplary Reasoning: Semantics, Pragmatics, and the Rational Force of Legal Argument by Analogy, 109 HARV. L. REV. 923, 972 (1996) (defining “rule” in a “logically spare manner” as “a prescriptive proposition that has a logical structure the most abstract form of which is reflected in the standard conditional proposition, either propositional (‘if P then Q’) or predicate (‘for all x, if x is an F then x is a G’)”). 4 See, e.g., TERENCE ANDERSON & WILLIAM TWINING, ANALYSIS OF EVIDENCE: HOW TO DO THINGS WITH FACTS BASED ON WIGMORE’S SCIENCE OF JUDICIAL PROOF 108-55 (1991) (concluding that “Wigmorean charts are a species of what today are sometimes described as ‘directed acyclic graphs’”); JOSEPH B. KADANE & DAVID A. SCHUM, A PROBABILISTIC ANALYSIS OF THE SACCO AND VANZETTI EVIDENCE 66-74 (1996) (developing inference networks as directed acyclic graphs with the root node – the ultimate issue to be proved – at the top, and the chains of reasoning extending from the evidence at the bottom upward to the root node); DAVID A. SCHUM, EVIDENTIAL FOUNDATIONS OF PROBABILISTIC REASONING 156-94 (1994) (interpreting Wigmorean evidence charts as “directed acyclic graphs whose nodes indicate propositions and whose arcs represent fuzzy probabilistic linkages among these nodes”); DOUGLAS WALTON, LEGAL ARGUMENTATION AND EVIDENCE 338-48 (2002) (discussing argument diagramming). Vern R. Walker Page 4 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite Vaccine Injury Table” of the Vaccine Act; second, that “there is a causal relationship between the vaccination and the injury”; and finally, that other conditions are met, concerning where the vaccination occurred, etc. (In this drawing, as in all the other drawings in this paper, the implication tree shown is only a partial tree. The complete tree incorporating all related rules would be quite extensive.) The model also shows that the second condition (causation) can be established in turn if either “there is a statutorily prescribed presumption of causation” or “there was ‘causation in fact’ between the vaccination and the injury.” Finally, this entire line of reasoning can be defeated by proof that “the injury is due to ‘factors unrelated to the administration of the vaccine.’” This defeating possibility is shown by the connective “UNLESS,” inserted just below the ultimate issue at the top. Figure 1: Partial Implication Tree for the Vaccine Act Vern R. Walker Page 5 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite In general, therefore, an implication tree is an inverted tree with the root node at the top (representing the ultimate issue of fact to be proved) and branches extending downward (representing all of the legally recognized lines of proof that can support a finding of that ultimate issue). The set of all “terminal propositions” at the ends of the branches of the implication tree contains all of the issues of fact relevant to proving the ultimate issue. Logical connectives link the levels within such trees – connectives such as conjunction, disjunction, and defeater (shown in Figure 1 as “AND,” “OR,” and “UNLESS,” respectively). When two levels of the tree are connected by “AND,” then the conclusion (the upper level) is true if all of the premises (the propositions on the lower level) are true. For the connective “OR,” the conclusion is true if one or more of the premises is true. When the connective is “UNLESS,” then the conclusion is false if the defeater premise is true. When courts decide cases and interpret the statutory wording of the Vaccine Act, they add new legal rules, and therefore modify the branches of the implication tree. For example, one issue of fact identified by the implication tree in Figure 1 is whether there was “causation in fact” between the vaccination and the injury. The case of Althen v. Secretary of Health and Human Services interpreted this issue as involving a conjunction of the three premises shown in Figure 2. Causation in fact is proved by establishing three propositions: “an acceptable ‘medical theory’ causally connects the vaccination and the injury”; “a ‘logical sequence of cause and effect’ 5 For a discussion of the logical properties of these truth-functional connectives, see Walker, “Default-Logic Paradigm,” supra note 1, at [10-13]. 6 418 F.3d 1274, 1278 (Fed.Cir. 2005). Vern R. Walker Page 6 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite shows that the vaccination was ‘the reason for’ the injury”; and “there is a ‘proximate temporal relationship’ between the vaccination and the injury.” When courts extend the statutory tree, they add new terminal propositions to the set of issues of fact – presumably, new issues that provide needed guidance to courts and factfinders in future cases. It is the combination of legislative and judicial authority, therefore, that creates the legal rules modeled by an implication tree. Figure 2: The Causation Rule of Althen Whereas traditional logic operates with two truth-values (“True / False”), it is more natural to model legal rules as having one of three truth-values (“True / Undecided / False”). When a legal case begins, all of the propositions in the implication tree are undecided. As the case proceeds, the parties might stipulate certain issues to be either true or false, or the judge may determine truth or falsehood as a matter of law, or the parties might introduce evidence and try to convince the trier of fact to evaluate particular issues as being true or false. These three Vern R. Walker Page 7 of 33 Visualizing the Dynamics around the Rule/Evidence Interface in Legal Reasoning Draft: Please Do Not Quote or Cite truth-values could be visualized in many ways, such as by coloring the outlines or fills of the