Reasoning with cases has been a primary focus of those working in AI and law who have attempted to model legal reasoning. In this paper we put forward a formal model of reasoning with cases which captures many of the insights from that previous work. We begin by stating our view of reasoning with cases as a process of constructing, evaluating and applying a theory. Central to our model is a view of the relationship between cases, rules based on cases, (...) and the social values which justify those rules. Having given our view of these relationships, we present our formal model of them, and explain how theories can be constructed, compared and evaluated. We then show how previous work can be described in terms of our model, and discuss extensions to the basic model to accommodate particular features of previous work. We conclude by identifying some directions for future work. (shrink)

This paper contributes to our formal understanding of the common law — especially the nature of the reasoning involved, but also its point, or justification, in terms of social coordination. I present two apparently distinct models of constraint by precedent in the common law, establish their equivalence, and argue for a perspective according to which courts are best thought of, not as creating and modifying rules, but as generating a social priority ordering on reasons through a procedure that is piecemeal, (...) distributed, and responsive to particular circumstances. (shrink)

This article argues that legal precedents do not create rules, but rather create a special type of reason in favour of a decision in later cases. Precedents are often argued to be analogous to statutes in their law-creating function, but the common law practice of distinguishing is difficult to reconcile with orthodox accounts of the function of rules. Instead, a precedent amounts to a decision on the balance of reasons in the case before the precedent court, and later courts are (...) required to decide cases on the basis that the earlier decision was correctly decided. (shrink)

This paper describes one way in which a precise reason model of precedent could be developed, based on the general idea that courts are constrained to reach a decision that is consistent with the assessment of the balance of reasons made in relevant earlier decisions. The account provided here has the additional advantage of showing how this reason model can be reconciled with the traditional idea that precedential constraint involves rules, as long as these rules are taken to be defeasible. (...) The account presented is firmly based on a body of work that has emerged in AI and Law. This work is discussed, and there is a particular discussion of approaches based on theory construction, and how that work relates to the model described in this paper. (shrink)

The doctrine of precedent, as it has evolved within the common law, has at its heart a form of reasoning—broadly speaking, alogic—according to which the decisions of earlier courts in particular cases somehow generalize to constrain the decisions of later courts facing different cases, while still allowing these later courts a degree of freedom in responding to fresh circumstances. Although the techniques for arguing on the basis of precedent are taught early on in law schools, mastered with relative ease, and (...) applied on a daily basis by legal practitioners, it has proved to be considerably more difficult to arrive at a theoretical understanding of the doctrine itself—a clear articulation of the underlying logic. (shrink)

This paper addresses the two extensional objections to the Humean Theory of Reasons—that it allows for too many reasons, and that it allows for too few. Although I won’t argue so here, manyof the other objections to the Humean Theoryof Reasons turn on assuming that it cannot successfully deal with these two objections.1 What I will argue, is that the force of the too many and the too few objections to the Humean Theorydepend on whether we assume that Humeans are (...) committed to a thesis about the weight of reasons—one I call Proportionalism. In particular, I’ll show how a version of the Humean Theorythat rejects Proportionalism can reasonablyhope to escape both the too many and the too few objections. This will constitute my defense of this version of the Humean Theory. But then, separately, I will argue that this defense of the Humean Theoryis not ad hoc. I’ll argue that Humeans have no reason to accept Proportionalism in the first place. Or at least, no weightyone. There are three parts to the paper. In Part 1 we introduce the Humean Theoryand the too few reasons objection. I’ll first layout the objection, and then layout the basis for a response on behalf of myfavored version of the Humean Theory. There will be an obvious objection to my defense— but it will turn out to depend on the assumption of Proportionalism. This will constitute myargument that the susceptibilityof the Humean Theoryto.. (shrink)

This paper takes up Berman and Hafner's (1993) challenge to model legal case-based reasoning not just in terms of factual similarities and differences but also in terms of the values that are at stake. The formal framework of Prakken and Sartor (1998) is applied to examples of case-based reasoning involving values, and a method for formalising such examples is proposed. The method makes it possible to express that a case should be decided in a certain way because that advances certain (...) values. The method also supports the comparison of conflicting precedents in terms of values, and it supports debates on the relevance of distinctions in terms of values. (shrink)

This paper shows how two models of precedential constraint can be broadened to include legal information represented through dimensions. I begin by describing a standard representation of legal cases based on boolean factors alone, and then reviewing two models of constraint developed within this standard setting. The first is the “result model”, supporting only a fortiori reasoning. The second is the “reason model”, supporting a richer notion of constraint, since it allows the reasons behind a court’s decisions to be taken (...) into account. I then show how the initial representation can be modified to incorporate dimensional information and how the result and reason models can be adapted to this new dimensional setting. As it turns out, these two models of constraint, which are distinct in the standard setting, coincide once they are transposed to the new dimensional setting, yielding exactly the same patterns of constraint. I therefore explore two ways of refining the reason model of constraint so that, even in the dimensional setting, it can still be separated from the result model. (shrink)

This paper gives an account of dimensions in the reason model found in Horty : 1–33, 2011), Horty and Bench-Capon and Rigoni :133–160, 2015. doi: 10.1007/s10506-015-9166-x). The account is constructed with the purpose of rectifying problems with the approach to incorporating dimensions in Horty, namely, the problems arising from the collapse of the distinction between the reason model and the result model on that approach. Examination of the newly constructed theory revealed that the importance of dimensions in the reason model (...) lies in their ability to establish weighings between reasons/factors of the same polarity. This permits past cases to constrain future cases in ways they could not on the reason model with just factors. The paper then discusses how dimensions might be established from a case base and how dimensions that are incomplete in various aspects might be dealt with in the theory. It closes with comparisons to other work in the literature on AI and Law and suggestions for further improvement of the reason model. (shrink)

The result model of precedent holds that a legal precedent controls a fortiori cases—those cases, that is, that are at least as strong for the winning side of the precedent as the precedent case itself. This paper defends the result model against some objections by Larry Alexander, drawing on ideas from the field of Artificial Intelligence and Law in order to define an appropriate strength ordering for cases.

Studies the principles which govern decision making under common law.

In this short note, we discuss several aspectsof dimensions and the related constructof factors. We concentrate on those aspectsthat are relevant to articles in this specialissue, especially those dealing with the analysisof the wild animal cases discussed inBerman and Hafner's 1993 ICAIL article. We reviewthe basic ideas about dimensions,as used in HYPO, and point out differences withfactors, as used in subsequent systemslike CATO. Our goal is to correct certainmisconceptions that have arisen over the years.