Jaap Hage

Reasoning with Rules

According to the semantic notion of logical validity, an argument is valid if the truth of its premises guarantees the truth of its conclusion. In chapter I, I tried to make it plausible that this semantic notion of validity is not very suitable if we are dealing with rules. The elaborate discussion in chapter II of reasons and their relation to principles, goals and rules, should have substantiated this claim.

Hard cases: a procedural approach

Much work on legal knowledge systems treats legal reasoning as arguments that lead from a description of the law and the facts of a case, to the legal conclusion for the case. The reasoning steps of the inference engine parallel the logical steps by means of which the legal conclusion is derived from the factual and legal premises. In short, the relation between the input and the output of a legal inference engine is a logical one. The truth of the conclusion only depends on the premises, and is independent of the argument that leads to the conclusion.This paper opposes the logical approach, and defends a procedural approach to legal reasoning. Legal conclusions are not true or false independent of the reasoning process that ended in these conclusions. In critical cases this reasoning process consists of an adversarial procedure in which several parties are involved. The course of the argument determines whether the conclusion is true or false. The phenomenon of hard cases is used to demonstrate this essential procedural nature of legal reasoning.Dialogical Reason Based Logic offers a framework that makes it possible to model legal dialogues. We use Dialogical Reason Based Logic to specify hard cases in dialogical terms. Moreover, we analyse an actual Dutch hard case in terms of Dialogical Reason Based Logic, to demonstrate both the possibilities and the shortcomings of this approach.It turns out that there is no one set of rational dialogue rules. There are many concurring sets of rules that govern particular types of dialogues. The rules for legal procedures are as much part of the law as the more substantial rules. As a consequence, it is not possible to offer an universal set of dialogue rules. Dialogical Reason Based Logic rather provides a framework which can be filled with dialogue rules that determine which dialogues are valid and which ones are invalid.

A theory of legal reasoning and a logic to match

This paper describes a model of legal reasoning and a logic for reasoning with rules, principles and goals that is especially suited to this model of legal reasoning. The paper consists of three parts. The first part describes a model of legal reasoning based on a two-layered view of the law. The first layer consists of principles and goals that express fundamental ideas of a legal system. The second layer contains legal rules which in a sense summarise the outcome of the interaction of the principles and goals for a number of case types. Both principles, goals and rules can be used in legal arguments, but their logical roles are different. One characteristic of the model of legal reasoning described in the first part of the paper is that it takes these logical differences into account. Another characteristic is that it pays serious attention to the phenomena of reasoning about the validity and acceptance of rules, respectively principles and goals, and about the application of legal rules, and the implications of these arguments for the use of rules, principles and goals in deriving legal conclusions for concrete cases.The second part of the paper first describes a logic (Reason-Based Logic) that is especially suited to deal with legal arguments as described in terms of the previously discussed model. The facilities of the logic are illustrated by means of examples that correspond to the several aspects of the model.The third part of the paper deals with a number of logico-philosophical reflections on Reason-Based Logic. The occasion is also used to compare these presuppositions with theories of defeasible reasoning based on the comparison of arguments.

An Integrated View on Rules and Principles

In the law, it is generally acknowledged that there are intuitive differences between reasoning with rules and reasoning with principles. For instance, a rule seems to lead directly to its conclusion if its condition is satisfied, while a principle seems to lead merely to a reason for its conclusion. However, the implications of these intuitive differences for the logical status of rules and principles remain controversial.A radical opinion has been put forward by Dworkin (1978). The intuitive differences led him to argue for a strict logical distinction between rules and principles. Ever since, there has been a controversy whether the intuitive differences between rules and principles require a strict logical distinction between the two. For instance, Soeteman (1991) disagrees with Dworkins opinion, and argues that rules and principles cannot be strictly distinguished, and do not have a different logical structure.In this paper, we claim that the differences between rules and principles are merely a matter of degree. We give an integrated view on rules and principles in which rules and principles have the same logical structure, but different behavior in reasoning. In this view, both rules and principles are considered to consist of a condition and a conclusion. The observed differences between rules and principles are, in our view, the result of different types of relations that they have with other rules and principles. In the integrated view, typical rules and typical principles are the extremes of a spectrum.We support our claim by giving an explicit formalization of our integrated view using the recently developed formal tools provided by Reason-Based Logic. As an application of our view on rules and principles, we give three ways of reconstructing reasoning by analogy.

The law as a dynamic interconnected system of states of affairs: a legal top ontology

Abstract In this paper, an abstract model of the law is presented that has three primitives: states of affairs, events and rules. The starting point of the abstract model is that the law is a dynamic system of states of affairs which are connected by means of rules and events. The abstract model can be regarded as a top ontology of the law, that can be applied to legal knowledge representation. After an elaboration of the three primitives, the uses of the abstract model are illustrated by the analysis of central topics of law. Then we discuss heuristic guidelines for legal knowledge representation that are suggested by the abstract model. The paper concludes with a comparison with related work. The appendix contains a formalism for the abstract model.

Monological reason-based logic: a low level integration of rule-based reasoning and case-based reasoning

This paper contains an informal introduction to a theory about legal reasoning (reason-based logic) that takes the notion of a reason to be central. Arguing for a conclusion comes down to first collecting the reasons that plead for and against the conclusion, and second weighing them. The paper describes how we can establish the presence of a reason and how we can argue whether the reasons for or the reasons against the conclusion prevail. It also addresses the topic of meta-level reasoning about the use of rules in concrete cases. It is shown how both rule-based reasoning and case-based reasoning are naturally incorporated in the theory of reason-based logic.

Formalizing legal coherence

This paper briefly argues for a (particular variant of) a coherence theory of legal justification and theory construction. It does so by placing coherentism in a tradition of general epistemology and practical reasoning. One part of the theory, namely the part that deals with the relation between abstract goals and concrete regulations, is described in detail, and formalized.

Dialectical models in artificial intelligence and law

Dialogues and dialectics have come to playan important role in the field of ArtificialIntelligence and Law. This paper describes thelegal-theoretical and logical background of this role,and discusses the different services into whichdialogues are put. These services include:characterising logical operators, modelling thedefeasibility of legal reasoning, providing the basisfor legal justification and identifying legal issues,and establishing the law in concrete cases. Specialattention is given to the requirements oflaw-establishing dialogues.

Law and defeasibility

The paper consists of three parts. In the first part five kinds of defeasibility are distinguished that is ontological, conceptual, epistemic, justification and logical defeasibility. In the second part it is argued that from these, justification defeat is the phenomenon that plays a role in legal reasoning. In the third part, the view is defended that non-monotonic logics are not necessary to model justification defeat, but that they are so to speak the natural way to model this phenomenon.

Legal Knowledge about What

We assume, in contrast to many legal realists, that law is a part of reality. Law exists because people believe in law, but law is not identical with beliefs. Law supervenes on human beliefs, preferences, actions, dispositions and artefacts. Moreover, the morally binding personal interpretation of the law supervenes on two things together: on the individual?s knowledge of legal institutions and on moral obligation. The first supervenes in its turn on mutual beliefs; the second supervenes on motivations and dispositions of the individual, provided that she is morally sensitive and rational. Personal interpretation of law converts into social law, if other persons on the basis of overriding reasons do not contest it. Morally binding social law supervenes on moral motivation that is triggered by institutions that supervene on mutual beliefs.