An Introduction to Legal Reasoning [Paperback]

The author describes his book as an attempt to give a general description of the process of legal reasoning in case law and in statutorial and constitutional interpretation. He emphasizes right at the beginning that the law should not be viewed as a known system of rules that are applied by a judge, that legal rules are never clear, and that a requirement for such clarity would make society impossible. Ambiguity in the rules he says, allows collective participation to resolve the ambiguity. Such a characterization of legal rules by Levi prohibits an axiomatic or formal approach to legal reasoning, and this will make the problem of creating automated legal reasoners much more difficult.

Interestingly, Levi quotes Aristotle in asserting that the pattern of legal reasoning consists of reasoning by example, and that it follows a three-step process: With the doctrine of precedent assumed throughout, a proposition describing a particular case is made into law and then this rule is applied to a situation that is similar to these. Thus: 1. The cases are shown to be similar. 2. The rule of law in the first case is announced 3. This rule is then applied to the second case. It is the finding of similarity in both cases that would entail, in the context of a legal reasoning machine, the use of data mining techniques coupled with a formalization of the Aristotelian "reasoning by example" that is discussed by Levi.

An interesting part of Levi's discussion on the determination of similarity (or difference) is that this determination is dependent on the judge. When a statute does not exist, and case law is being considered, the judge is free to dismiss teh facts that the prior judge may have considered important. The doctrine of "ratio decidendi" in legal philosophy, and has been the subject of intense investigation. A formal or computational model of ratio decidendi must come to terms with this tension between precedent and judicial discretion.

In addition, Levi argues, the rules are discovered in the process of determining the similarities (or differences). This dynamism in legal reasoning is not too different from what happens in scientific research, for in the latter new laws (rules) are discovered in the process of interpreting new data that has been acquired by new experiments. The data may then have to be re-interpreted in the light of the new laws (rules) that are formulated. Future data that is similar to this data will then be interepreted under these new rules. Future data that is very different from this may entail a new set of rules be invented (discovered) to deal with this difference.

The issue then, Levi explains, is to when one must view different cases as the same. An intersection of the set of facts of two cases entails a general rule be applied. This "reasoning" is imperfect, Levi argues, since the conclusions were arrived at by a process that was not transparent. Levi summarizes this as a process in which the classification changes as the classification is made, i.e., the rules change as they are applied. This might seem troubling to some, but Levi explains that such a situation is desirable since without it, new ideas could not enter into the legal process. Thus a static view of the legal process where consequences are derived from a closed system of rules is not useful in legal reasoning. In addition, Levi argues, fairness to the parties involved in litigation is served best by this ambiguity in legal categories. The commonality of the ideas of society coupled with the contributions made by legal experts both serve to shape the law.

Levi also discusses the role that reasoning by example has in the interpretation of case law, statutes, and the Constitution. The intent of the legislature enters into the consideration of the statute by subsequent judges, and so these judges have less flexibility in applying a statute than they would in the consideration of case law. Interestingly, Levi argues that the case for constitutional law is different, in that the judge has more freedom than was the case for statutorial or case law. The court can be inconsistent in this case, says Levi, but this freedom is masked under the guise of a search for the intent of the framers of the Constitution or as a characterization of the Constitution as a "living document".