The study presented in this book was entered upon by me from a legal point of view. 'Legal logic' has been known for a long time, concerning itself with the methodology of legal and in particular judicial reasoning. In modern days, however, this 'legal logic' is sometimes also connected with modern formal logic, as it has been developed in the works of G. Boole, A. de Morgan, G. Frege, C.S. Peirce, E. Schroder, G. Peano, A.N. Whitehead, B. Russell and others. For me this gave rise to the as yet not very specific question about the meaning of modern symbolic logic for law. Already in an early stage it appeared that, although traditional legal logic and modern symbolic logic both concern logic, this may not create the misapprehension that a similar matter is at issue. Both concern themselves (among other things) with reasonings and reasoning. Traditional legal logic is, however, as it was said by the German legal theoretician K. Engisch: "a material logic that wants us to reflect on what we have to do if we -within the limits of actual possibility- wish to reach true, or at least correct judgements" (Engisch, 1964, p.5). Modern symbolic logic on the other hand is not concerned with the truth or correctness of the result of an argument, but with its validity, i.e. the question when or under which conditions the truth (correctness) of the conclusion is guaranteed by the truth (correctness) of the premisses.

At least since plato and Aristotle, thinkers have pondered the relationship between philosophical arguments and the "sophistical" arguments offered by the Sophists -- who were the first professional lawyers. Judges wield substantial political power, and the justifications they offer for their decisions are a vital means by which citizens can assess the legitimacy of how that power is exercised. However, to evaluate judicial justifications requires close attention to the method of reasoning behind decisions. This new collection illuminates and explains the political and moral importance in justifying the exercise of judicial power.

Use of argumentation methods applied to legal reasoning is a relatively new field of study. The book provides a survey of the leading problems, and outlines how future research using argumentation-based methods show great promise of leading to useful solutions. The problems studied include not only these of argument evaluation and argument invention, but also analysis of specific kinds of evidence commonly used in law, like witness testimony, circumstantial evidence, forensic evidence and character evidence. New tools for analyzing these kinds of evidence are introduced.

This book presents the current state of the art regarding the application of logical tools to the problems of theory and practice of lawmaking. It shows how contemporary logic may be useful in the analysis of legislation, legislative drafting and legal reasoning concerning different contexts of law making. Elaborations of the process of law making have variously emphasised its political, social or economic aspects. Yet despite strong interest in logical analyses of law, questions remains about the role of logical tools in law making. This volume attempts to bridge that gap, or at least to narrow it, drawing together some important research problems—and some possible solutions—as seen through the work of leading contemporary academics. The volume encompasses 20 chapters written by authors from 16 countries and it presents diversified views on the understanding of logic (from strict mathematical approaches to the informal, argumentative ones) and differentiated choices concerning the aspects of law making taken into account. The book presents a broad set of perspectives, insights and results into the emerging field of research devoted to the logical analysis of the area of creation of law. How does logic inform lawmaking? Are legal systems consistent and complete? How can legal rules be represented by means of formal calculi and visualization techniques? Does the structure of statutes or of legal systems resemble the structure of deductive systems? What are the logical relations between the basic concepts of jurisprudence that constitute the system of law? How are theories of legal interpretation relevant to the process of legislation? How might the statutory text be analysed by means of contemporary computer programs? These and other questions, ranging from the theoretical to the immediately practical, are addressed in this definitive collection.

This book intends to unite studies in different fields related to the development of the relations between logic, law and legal reasoning. Combining historical and philosophical studies on legal reasoning in Civil and Common Law, and on the often neglected Arabic and Talmudic traditions of jurisprudence, this project unites these areas with recent technical developments in computer science. This combination has resulted in renewed interest in deontic logic and logic of norms that stems from the interaction between artificial intelligence and law and their applications to these areas of logic. The book also aims to motivate and launch a more intense interaction between the historical and philosophical work of Arabic, Talmudic and European jurisprudence. The publication discusses new insights in the interaction between logic and law, and more precisely the study of different answers to the question: what role does logic play in legal reasoning? Varying perspectives include that of foundational studies (such as logical principles and frameworks) to applications, and historical perspectives.

Studies in Legal Logic is a collection of nine interrelated papers about the logic, epistemology and ontology of law. All of the papers were written after the publication of the author’s Reasoning with Rules and supplement the issues addressed therein. Some of the papers are new; others have been revised substantially after the publication of their original versions. The emphasis is on analysis, not on logical technicalities. Studies in Legal Logic contains chapters about the nature of norms, the role of coherence in the law, the nature of defeasibility, the role of dialectics in law and artificial intelligence, the statics and dynamics of the law, and the consistency of rules. Moreover, it contains a new, simplified and yet more powerful version of Reason-based Logic and extensive examples of how it can be used for the analysis of legal reasoning. The examples deal with legal theory construction, case-based reasoning, and judicial proof.

This volume explores the relation between legal reasoning and logic from both a historical and a systematic perspective. The topics addressed include, among others, conditional legal acts, disjunctions in legal acts, presumptions and conjectures, conflicts of values, Jørgensen ́s Dilemma, the Rhetor ́s Dilemma, the theory of legal fictions and the categorization of contracts. The unifying problematic of these contributions concerns the conditional structures and, more particularly, the relationship between legal theory and legal reasoning in the context of conditions. The contributions in this work constitute the first results of the ANR-DFG joint research project “JuriLog” (Jurisprudence and Logic), which aims at fostering the cooperation between legal scholars and philosophers. On the one hand, lawyers and legal scholars have an interest in emphasizing the logical character of legal reasoning. In this respect, the present enquiry examines the question of how logic, especially newer forms of dialogical logic, can be made fruitful as a significant area of philosophy for jurisprudence and legal practice. On the other hand, logicians find in legal reasoning a striving towards clear definitions and inference-procedures that is relevant to their discipline. In order to fully understand such reciprocal relationships, it is necessary to bridge the gap between law, logic and philosophy in contemporary academic research. The essays collected in this volume all work towards this common goal. The book is divided in three sections. In the first part, the strong relation between Roman Law and logic is explored with respect to the analysis of disjunctive statements in legal acts. The second part focuses on Leibniz ́s legal theory. The third part, finally, is dedicated to current interactions between law and logic.

This book describes extensions of deontic logic. Deontic logic is a branch of philosophical logic involving reasoning with norms, obligations, prohibitions and permissions. The extensions concern the logical structure of legal rules and legal reasoning. Their function is to improve the representation of legal knowledge and enhance deontic logic through increased expressibility. The resulting formulas acquire new meanings, not expressible in standard deontic logic, which are subject to fresh interpretations. The author offers an extensive analysis of the representation of actors, to whom the norms are directed, and authorities who enact the norms. Moreover, a distinction is made between enactment and applicability. A modality of enactment can be used to express inconsistent enacted norms in a consistent way. An authority-hierarchy is introduced to filter out the applicable norms from the set of enacted norms. Some related philosophical questions will be discussed regarding the applications of formalisms that are intrinsic to practical science with respect to `consistency' and `universality'. The formalisms and applications considered here are relevant for law, philosophy and computer science, with a special focus on the improvement of legal expert systems and intelligent support for legal professionals.