Jaap Hage

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.

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.

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.

This article argues that it is possible to hold autonomous agents themselves, and not only their makers, users or owners, responsible for the acts of these agents. In this connection autonomous systems are computer programs that interact with the outside world without human interference. They include such systems as ‘intelligent’ weapons and self-driving cars. The argument is based on an analogy between human beings and autonomous agents and its main element asserts that if humans can be held responsible, so can, in principle, autonomous agents, as humans are more like autonomous agents than is often assumed.

This article describes how the facts in social reality take an intermediate position between objective facts and purely subjective ‘facts’. In turn, these social facts can be subdivided into constructivist and non-constructivist facts. The defining difference is that non-constructivist facts are completely determined by an approximate consensus between the members of a social group, while constructivist facts are founded in such a consensus but can nevertheless be questioned. Ought fact are such constructivist facts. Because they are founded in social reality, a naturalistic theory of ought facts is attractive. Because constructivist facts are always open to questioning, we can explain why the facts in social reality may found ought facts but are nevertheless not the final word about them.

This paper develops the theory that a set of rules is consistent if it is not possible that (1) the conditions of the rules in the set are all satisfied, (2) there is no exception to either one of the rules, and (3) the consequences of the rules are incompatible. To this purpose the notion of consistency is generalised to make it cover rules and is relativised to some background of constraints.This theory is formalised by means of Rule Logic, in which rules are treated as constraints on the possible worlds in which they exist. Rule Logic itself is introduced by giving a model-theory for it. It is characterised by means of constraints on worlds that are possible according to Rule Logic.

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 Dworkin's opinion, and argues that rules and principles cannot be strictly distinguished, and do not have a different logical structure.

This book features essays that investigate the nature of legal validity from the point of view of different traditions and disciplines. Validity is a fascinating and elusive characteristic of law that in itself deserves to be explored, but further investigation is made more acute and necessary by the production, nowadays, of soft law products of regulation, such as declarations, self-regulatory codes, and standardization norms. These types of rules may not exhibit the characteristics of formal law, and may lack full formal validity but yet may have a very real impact on people's lives. The essays focus on the structural properties of hard and soft legal phenomena and the basis of their validity. Some propose to redefine validity: to allow for multiple concepts instead of one and/or to allow for a gradual concept of validity. Others seek to analyze the new situation by linking it to familiar historical debates and well-established theories of law. In addition, coverage looks at the functions of validity itself. The discussion considers both international law as well as domestic law arrangements. What does it mean to say that something is valid? Should we discard validity as the determining aspect of law? If so, what does this mean for our concept of law? Should we differentiate between kinds of validity? Or, can we say that rules can be "more" or "less" valid? After reading this book, practitioners, scholars and students will have a nuanced understanding of these questions and more. Chapter 6 is available open access under a Creative Commons Attribution 4.0 International License via link.springer.com.

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.

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.

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 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.

This paper deals with two issues in the field of reasoning by analogy in the law. The one issue is whether there exists such a thing as analogous rule application, or whether there is only the ‘normal’ application of a broadened rule. It is argued that if rules, as the entities made by a legislator, are distinguished from generalised solutions for cases, the idea of analogous application of rules makes sense. It is also shown how the so-called ‘reason-based model of rule application’, in contrast to the traditional modus ponens or subsumption model, makes it easy to give a logical account of analogous rule application. The other issue is how to argue logically about whether two cases are sufficiently similar to adopt the outcome of the one case for the other case. Section 3 provides a general logical model to establish this. The model is based on the comparison of the reasons for and against a particular solution in the two cases.

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.

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.

Are the cognitive sciences relevant for law? How do they influence legal theory and practice? Should lawyers become part-time cognitive scientists? The recent advances in the cognitive sciences have reshaped our conceptions of human decision-making and behavior. Many claim, for instance, that we can no longer view ourselves as purely rational agents equipped with free will. This change is vitally important for lawyers, who are forced to rethink the foundations of their theories and the framework of legal practice. Featuring multidisciplinary scholars from around the world, this book offers a comprehensive overview of the emerging field of law and the cognitive sciences. It develops new theories and provides often provocative insights into the relationship between the cognitive sciences and various dimensions of the law including legal philosophy and methodology, doctrinal issues, and evidence.

Brouwer argued against a vision of the law in which moral considerations partly determine the contents of the law. He did this for moral reasons, mainly because of the uncertainty such a vision would cause. This seems a strange view because it means that the nature of the law would depend on moral considerations concerning legal certainty. Most of the present paper is devoted to exploring two conceptions of the law, law as social fact and law as practical reason. It is argued that a view like Brouwer’s fits in the law as practical reason conception and is therefore not so strange as might seem at first sight

This book is exceptional in the sense that it provides an introduction to law in general rather than the law of one specific jurisdiction, and it presents a unique way of looking at legal education. It is crucial for lawyers to be aware of the different ways in which societal problems can be solved and to be able to discuss the advantages and disadvantages of different legal solutions. In this respect, being a lawyer involves being able to reason like a lawyer, even more than having detailed knowledge of particular sets of rules. Introduction to Law reflects this view by focusing on the functions of rules and on ways of arguing the relative qualities of alternative legal solutions. Where 'positive' law is discussed, the emphasis is on the legal questions that must be addressed by a field of law, and on the different solutions which have been adopted by, for instance, the common law and civil law tradition. The law of specific jurisdictions is discussed to illustrate possible answers to questions such as when the existence of a valid contract is assumed.