Jaap Hage, Reasoning with Rules: An Essay on Legal Reasoning and Its Underlying Logic. Law and Philosophy Library

Jaap Hage is one of the mysterious members of the AI and Law community: someone capable of significant insights lost in insignificant prose, someone who delivers scholarship and erudition through burbling lines of symbols. It is therefore with eagerness and fear that one approaches his major work to date, Reasoning with Rules (Kluwer, 1997). A good book is an image of its author, and this book is in fact a faithful portrait of Jaap Hage’s thought. It is an important addition to the Law and Philosophy Library series because it addresses important issues in an accessible way. The surprise is that the book is not really written for the AI and Law community, which has been the cauldron for the themes that emerge in the book. It is a book for the wider philosophical legal readership, an exporting of the ideas of AI to the philosophy of law. It is a book that I am happy to say AI and Law researchers will be quick to recommend to outsiders. The book is a meditation on the formal modeling of rule application. It begins by arguing for defeasibility, then brushes through Raz (exclusions), Toulmin (argumentation), and Naess (balancing reasons), while commenting on some philosophy of rules (Anscombe and Searle). The book is preoccupied with distinctions: between rules that explain and rules that justify, brute facts and institutional facts, constitutive and normative rules, rules and reasons, social rules and social reasons, social reasons and personal reasons, goals and reasons, principles and rules, and so forth. The resulting map is the kind of thing that would result from a survey course in the philosophy of rules. It is unfortunate that Hage chooses to be glib in his treatment of these distinctions, taking a common language philosophy approach, rather than delving into the formal distinctions that modelers might make that would reflect philosophical differences. One important topic for Hage is deontic collapse, which refers to the way