(1) Computer/Law Institute (2) Section Law and Informatics
Vrije Universiteit Amsterdam Department of Metajuridica
The Netherlands Universiteit Maastricht
email@example.com, and firstname.lastname@example.org
(The second author gladly acknowledges the financial support by the Dutch National Programme Information Technology and Law (ITeR) for the research reported in this paper (project number 01437112) .)
Versions of this paper have been presented at the 13th BILETA Conference [Lodder and Verheij 1998] and at the 2nd French-American Conference on Artificial Intelligence and Law [Verheij and Lodder 1998].
This is a refereed article published on: 30 June 1999
Citation: Lodder A et al, 'Computer-Mediated Legal Argument: Towards new Opportunities in Education', 1999 (2) The Journal of Information, Law and Technology (JILT).
Argumentation is a key activity of lawyers. Therefore in law school teaching argumentation is essential. Information technology can provide useful support in argumentation courses. New opportunities come from a recent topic of research in the field AI & Law, viz. computer-mediated legal argument (e.g., Gordon, Lodder, Loui). In this paper, we suggest how computer-mediated legal argument can provide opportunities for teaching legal argument. The main part of the paper is devoted to a description of two experimental systems for computer-mediated legal argument, viz. Lodder's DiaLaw and Verheij's Argue!.
The starting point for the research on computer-mediated legal argument is that a computer system can support lawyers by mediating the process in which they draft and generate arguments: the system can administer and supervise the argument process by keeping track of the reasons adduced and the conclusions drawn, and by checking whether the users of the system obey the pertaining rules of argument, e.g., those related to the division of burden of proof.
Computer-mediated legal argument poses a new problem: how should an argument be presented to the users of the mediating system? Especially with regards to recently developed logical tools (e.g., Hage, Prakken, Sartor, Verheij), there is little experience with argument presentation. There is a natural division of approaches to argument presentation in two classes: the verbal and the graphical approaches. In the verbal approach, the argument is mainly presented in a verbal style, for instance in the form of a text or a written-out dialog. In the graphical approach, the argument is mainly presented in a graphical style, for instance in the form of a tree of sentences.
In the paper, we reconstruct elements of a Dutch Supreme Court case on tort law (March 20, 1992) and its sequel at the Court of Justice of The Hague (September 15, 1994) in two prototypical systems for the mediation of legal argument, viz. DiaLaw by Lodder and Argue! by Verheij. The first system takes the verbal approach; the second system takes the graphical approach.
The two approaches to argument presentation are discussed against the background of teaching legal argument. We speculate on the possible uses of computer-mediated legal argument in teaching argumentation skills. We expect that neither of the two approaches can be fully satisfactory for teaching legal argument if it is taken to its extreme, and recommend that a hybrid combination of verbal and graphical elements is striven for.
Keywords: computer-mediated legal argument, legal education, legal IT, AI and law
Argumentation is a key activity of lawyers. Therefore in law school teaching argumentation is essential. Information technology can provide useful support in argumentation courses. For instance, recently Aleven and Ashley  have shown that instructing case-based argumentation skills by their CATO system led to improvement in students' basic argumentation skills that was comparable to the improvement realised by an experienced legal writing instructor.
One could also think of systems teaching classical logic, such as first-order predicate logic. Several systems are available. An example is the acclaimed Tarski's World by Barwise and Etchemendy , that teaches the meaning of the language of first-order predicate logic by depicting a block's world on screen, in which sentences can be interpreted.
Notwithstanding their availability, systems meant for teaching classical logic are hardly used in law school, since only the basic elements of classical logic are considered essential for lawyers. Certainly, classical logic can be used to analyse the argument structure of legal texts and discourse. However, the resulting analysis is (by the very nature of classical logic) rather limited. Probably, the main reason for teaching elements of classical logic in law school (if taught at all) is that it serves the purpose of training general analytical skills, which is useful for anyone.
Recently, much research has been devoted to legal logic.1 In this research program, attempts are made to include legal argument forms into logic. Some of the topics addressed are exceptions, the weighing of conflicting reasons, rule applicability and the division of burden of proof. Arguments using these have long been adopted by lawyers, but in an intuitive way and without a systematic basis. Legal logic attempts to provide this basis. Verheij, Hage and Lodder  provide an overview of the recent research on legal logic with examples from Dutch tort law.
Supposedly, legal logic has more to offer that is readily useful for law school than classical logic,2 since the argument forms that can be analysed by legal logic, occur regularly in actual legal argument. The question arises how the findings of legal logic could be taught in an effective way.
New opportunities come from a recent topic of research in the field AI & Law, viz. computer-mediated legal argument (e.g., Loui , Gordon , Lodder , Verheij [1998a, 1998b]). The starting point for the research on computer-mediated legal argument is that a computer system can support lawyers by mediating the process in which they draft and generate arguments: the system can administer and supervise the argument process by keeping track of the reasons adduced and the conclusions drawn, and by checking whether the users of the system obey the pertaining rules of argument, e.g., those related to the division of burden of proof.
A difficulty for such systems is the presentation of arguments. There is a natural distinction between two approaches to argument presentation, viz. the verbal and the graphical approach. The first presents arguments in a verbal way. The chosen language can be natural language (or a fragment of natural language) or a formal language, for instance, that of predicate logic. Gordon's Pleadings Game  is an example of the verbal approach, using a formal language. The second approach presents arguments in a graphical way. The structure of arguments is somehow reflected in its graphical layout. An example is Loui et al.'s Room 5 (1997) , where sentences are shown in boxes. If one box is inside another box, the sentence in the first box expresses a reason for the conclusion in the second box.
As far as legal systems for teaching argumentation-like skills are concerned, besides the already mentioned CATO-system only few of them are really used in practice or have left the stage of a prototype. Examples of legal systems for training students are OBLIGATIO by Fernhout et al.  (that was used in the early nineties to train law students in Maastricht), the LITES system by Span , the STATUTOR system (Routen , Centinia et al. ), the PROSA-system by Muntjewerff & Groothuismink , the system for international tax law by Lodder , and, recently, Bench-Capon et al. .
In this paper, we describe two mediation systems that have been developed at the Universiteit Maastricht that can serve as the starting point for future systems for teaching students legal argumentation. We will be brief about the argumentation theory behind the systems. The interested reader is referred to the work of Hage [1996, 1997], Lodder , and Verheij [1996, 1998a].
The first system, called DiaLaw, takes the verbal approach. It is a Prolog implementation of the dialog game for legal justification DiaLaw [Lodder & Herczog, 1995; Lodder, 1998]. The second system, called Argue!, takes the graphical approach. It is a Delphi implementation of the procedural model of argumentation with arguments and counterarguments CumulA [Verheij, 1996]. Both systems are prototypes for the mediation of legal argument. In our discussion of the two systems, we suggest opportunities for teaching legal argument.
In the following, we discuss an interesting case of Dutch tort law (section 2). The case is used to illustrate the two prototypical systems for the mediation of legal argument. First the system that takes the verbal approach is described (section 3), then the system that takes the graphical approach (section 4).