Formal Models of Balancing in Legal Cases

A JURIX 2014 tutorial

Cracow (Poland), 10 December 2014

Lecturers:

  • Henry Prakken, Department of Information and Computing Sciences, Utrecht University & Faculty of Law, University of Groningen, The Netherlands.
  • Giovanni Sartor, European University Institute, Fiesole, Florence & CIRSFID, University of Bologna, Italy.

Abstract:

Many legal cases involve the comparison, or balancing, or sets of reasons pro and con a decision. Reasons can be either boolean or multi-valued. In the past ten years various formal models of balancing reasons in legal cases have been proposed. This tutorial aims to give an introduction to these models, focussing especially on argument-scheme and reason-based approaches. This work is theoretically interesting as a contribution to AI & Law and legal theory but it can also be the basis for teaching reasoning and argumentation skills to legal decision makers and advocates who want to improve their practical reasoning skills in balancing problems.

Tutorial slides:

Henry Prakken
Giovanni Sartor (to be added)

Content and motivation:

Many legal cases involve the comparison, or balancing, or sets of reasons pro and con a decision. Reasons can be of different kinds: they can be boolean factors pro or con a decision (as in Aleven & Ashley's CATO system), many-valued dimensions relevant to a decision (as in Ashley & Rissland's HYPO system), goals achieved or violated by a decision, or values promoted or demoted by a decision. In the past ten years various formal models of balancing reasons in legal cases have been proposed and it is now timely to introduce their essentials and interrelations to a wider audience, to systematize and consolidate the state-of-the art. Moreover, formal models of balancing reasons in legal cases are also practically relevant, since many court cases involve some or other kind of balancing, and insight into the nature of balancing may help legal decision makers and advocates to improve their practical reasoning skills.

This tutorial will give an overview of the following models:

  • Argument scheme-based models. Some models adopt the argument-scheme paradigm, formulating argument schemes plus critical questions for balancing reasons and embedding their use in a formal system for argumentation, such as Dung's abstract argumentation frameworks, Bench-Capon's extension of these frameworks with values, or the ASPIC+ framework for structured argumentation. Discussed work will include the recent series of papers by Atkinson, Bench-Capon, Prakken and Wyner.
  • Reason-based models. Other models do not take arguments but reasons as the basic notion, and directly provide models of balancing reasons. Two models will be discussed: Horty's recent theory of precedential constraint in common law and Sartor's account of the logic of proportionality in teleological reasoning.

Outline of topics:

  1. History of AI & Law research on case-based reasoning
  2. Basic elements of formal models of argumentation
  3. Argument scheme approaches
  4. Yes-or-no factors
  5. Dimensions
  6. From factors to values
  7. A formal theory of precedential constraint in common law
  8. A logical account of proportionality in teleological reasoning

Intended audience:

Formal models of balancing in legal case-based reasoning are theoretically interesting as a contribution to AI & Law and legal theory. Moreover, they are also practically relevant, since many court cases involve some or other kind of balancing, and insight into the nature of balancing may help legal decision makers and advocates to improve their practical reasoning skills. Accordingly, the intended audience is twofold: researchers in AI & Law or legal theory interested in formal models of legal reasoning and legal argument; and lecturers interested in teaching legal reasoning and argument.

Prerequisite knowledge:

An analytical mind and familiarity with legal reasoning should suffice to follow most of the tutorial. Introductory knowledge of standard propositional logic is beneficial, as well as elementary knowledge of set theory and the theory of relations and functions. Knowledge of formal models of argumentation is also beneficial but not necessary; the tutorial will contain a brief introduction to such models.

Bibliography:

Trevor Bench-Capon has an excellent bibliography on Arguing with cases. The most relevant sections for this tutorial are Reconstructing factor-based reasoning, Values and Argumentation schemes. Some additional papers relevant to our tutorial are:

  • R. Alexy, On balancing and subsumption: a structural comparison. Ratio Juris 16 (2003): 3349.
  • G. Sartor, Reasoning with factors. Argumentation 19 (2005): 417432. [PDF]
  • G. Sartor, Doing Justice to Rights and Values: Teleological reasoning and proportionality. Artificial Intelligence and Law 218 (2010): 175-215. [PDF]
  • G. Sartor, The logic of proportionality: reasoning with non-numerical magnitudes. German Law Journal 14 (2013): 1419-1456. [PDF]
  • G. Sartor, Reasoning with Values: Quantitative Assessments Without Numbers. In K. Atkinson, H. Prakken & A. Wyner (eds.) From Knowledge Representation to Argumentation in AI, Law and Policy Making. A Festschrift in Honour of Trevor Bench-Capon on the Occasion of his 60th Birthday, pp. 213-234. College Publications, Londen, 2013. [PDF]
  • J.C. Hage, Comparing alternatives in the law. Artificial Intelligence and Law 12 (2005): 181-225.
  • J.C. Hage, B. Verheij & H.J. van den Herik, An integrated view on rules and principles. Artificial Intelligence and Law 6 (1998): 3-26. [PDF]
  • J. Horty, Rules and reasons in the theory of precedent. Legal Theory 17 (2011):1-33. [PDF]