Jaap Hage

This paper develops the theory that a set ofrules is consistent if it is not possible that (1)the conditions of the rules in the set are allsatisfied, (2) there is no exception to either one ofthe rules, and (3) the consequences of the rules areincompatible. To this purpose the notion ofconsistency is generalised to make it cover rulesand is relativised to some background of constraints.This theory is formalised by means of Rule Logic, inwhich rules are treated as constraints on thepossible worlds in which they exist. Rule Logicitself is introduced by giving a model-theory forit. It is characterised by means of constraints onworlds that are possible according to Rule Logic.

This paper deals with the questions of whether the law should be coherent and what this coherence would amount to. In this connection so‐called “integrated coherentism” is introduced. According to integrated coherentism, an acceptance set is coherent if and only if it contains everything that should rationally be accepted according to what else one accepts and does not contain anything that should rationally be rejected according to what else one accepts. Such an acceptance set is ideally a theory of everything, including amongst others standards for rational aceptance. On the assumption that the law, as a social phenomenon, is what the best theory about the law says it is, the law must be coherent, because the best theory of the law is part of an integratedly coherent theory of everything. This view is compatible with Raz's view that the law stems from different sources that need not be coherent in the sense that they consistently elaborate the same underlying principles or policies. Raz's view is not a consequence of integrated coherentism, however.

Rule-applying legal arguments are traditionally treated as a kind of syllogism. Such a treatment overlooks the fact that legal principles and rules are not statements which describe the world, but rather means by which humans impose structure on the world. Legal rules create legal consequences, they do not describe them. This has consequences for the logic of rule- and principle-applying arguments, the most important of which may be that such arguments are defeasible. This book offers an extensive analysis of the role of rules and principles in legal reasoning, which focuses on the close relationship between rules, principles, and reasons. Moreover, it describes a logical theory which assigns a central place to the notion of reasons for and against a conclusion, and which is especially suited to deal with rules and principles.

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.

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.

This paper argues the thesis that a particular style of reasoning, qualitative comparative reasoning (QCR), plays a role in at least three areas of legal reasoning that are central in AI and law research, namely legal theory construction, case-based reasoning in the form of case comparison, and legal proof. The paper gives an informal exposition of one particular way to deal with QCR, based on the author’s previous work on reason-based logic (RBL). Then it contains a substantially adapted formalisation of RBL, to make RBL suitable for dealing with QCR. The paper concludes with a brief discussion of related work.

Doctrinal legal science seems to lack a proper method and purpose. This interpretation clarifies its value. The backbone of the argu- ment consists of two theses. The first is that coherence—in a sense unusu- al in law—plays a crucial role in legal science. The second is that doctrinal legal science is a social enterprise and this should be consid- ered in attempts to understand it. Based on these, a picture of doctrinal legal science is given consisting of parallel distributed constructions of consistent, comprehensive and ex- pansive sets of legal beliefs. Given this, seeming weaknesses of doctri- nal legal science turn out to be actual strengths.

This paper aims at providing an account of juridical acts that forms a suitable starting point for the creation of computational systems that deal with juridical acts. The paper is divided into two parts. Because juridical acts will be analyzed as intentional changes in the world of law, the ‘furniture’ of this world, that consists broadly speaking of entities, facts and rules, plays a central role in the analysis. This first part of the paper deals with this furniture and its philosophical underpinnings, and at the same time introduces most of the logical apparatus that will be used to deal with it. The focus in the first part is on static and dynamic legal rules and their interplay in constituting the world of law

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.