Legal Taxonomy

In this post, I comment on Sherwin’s recent article Legal Taxonomy in the journal Legal Theory. It is a very lucid, thorough, and well-referenced discussion of the state-of-the-art in taxonomies of legal rules. By considering how legal taxonomies organise legal rules, we better understand current conceptions of legal rules by legal professionals. My take away message from the article is that the analysis of legal rules could benefit from some of the thinking in Linguistics and Computer Science, particularly in terms of how data is gathered and analysed.
Below, I briefly outline ideas concerning taxonomies and legal rules. Then, I present and comment on the points Sherwin brings to the fore.
Taxonomy is the practice and science of classification of items in a hierarchical IS-A relationship, where the items can be most anything. The IS-A relationship is also understood as subtypes or supertypes. For example, a car is a subtype of vehicle, and a Toyota is a subtype of car; we can infer that a Toyota is a subtype of vehicle. Each subtype has more specific properties than the supertype. In some taxonomies, one item may be a subtype of several supertypes; for example, a car is both a subtype of vehicle and a subtype of objects made of metal, however, not all vehicles are made of metal, nor are all things made from metal vehicles, which indicates that these types are distinct. Taxonomies are more specific than the related term ontologies, for which a range of relationships beyond the IS-A relationship may hold among the items such as is owned by or similar. In addition, ontologies generally introduce properties of elements in the class, e.g. colour, engine type, etc. Classifications in scientific domains such as Biology or Linguistics is intensely debated and revised. It would be expected that this would be even more so true in the legal domain which is comprised of intellectual evidence rather than empirical evidence as in the physical sciences and where the scientific method is not applied.
Legal Rules
First, let us be clear about what a legal rule is with a clear example following Professor David E. Sorkin’s example . A legal rule is a rule which determines whether some proposition holds (say of an individual) contingent on other propositions (the premises). For example, the state of Illinios assault statute specifies: “A person commits an assault when, without lawful authority, he engages in conduct which places another in reasonable apprehension of receiving a battery.” (720 ILCS 5/12-1(a)). We can analyse this into the legal rule:

    A person commits assault if

      1. the person engages in conduct;
      2. the person lacks lawful authority for the conduct;
      3. the conduct places another in apprehension of receiving a battery; and
      4. the other person’s apprehension is reasonable.

Optimally, each of the premises in a rule should be simple and be answerable as true or false. In this example, where all four premises are true, the conclusion, that the person committed assault, is true.
There are significant issues even with such simple examples since each of the premises of a legal rule may itself be subject to further dispute and consideration; the premises may be subjective (e.g. was the conduct intentional), admit degrees of truth (e.g. degree of emotional harm), or application of the rule may be subject to mitigating or aggravating circumstances. The determination of the final claim follows the resolution of these subsidiary disputes and considerations. In addition, some legal rules need not require all of the premises to be true, but allow a degree of counterbalancing evaluation of the terms.
The Sources of Legal Rules
Sherwin outlines the sources of the rules:

      Posited rules, which are legal rules as explicitly given by a legal authority such as a judge giving a legal decision.
      Attributed rules, which are legal rules that are drawn from a legal decision by a legal researcher rather than by a legal authority in a decision. The rule is implicit in the other aspects of the report of the case.
      Ideal rules, which are rules that are ‘ideal’ relative to some criteria of ideality, say morally or economically superior rules.

Purposes of Classification
In addition, we have the purposes or uses of making a classification of legal rules.

      Facilitating the discussion and use of law.
      Supporting the critical evaluation of law
      Influencing legal decision-making

In the first purpose, the rules are sorted into classes, which helps to understand and manage legal information. In Sherwin’s view, this is the most basic, formal, and least ambitious goal, yet it relies on having some taxonomic logic in the first place. The second purpose, the rules are evaluated to determine if they are serving the intended purpose as well as to identify gaps or inconsistencies. As Sherwin points out, the criteria of evaluation must then also be determined; however, this then relates to the criteria which guides the taxonomy in the first place, a topic we touch on below. The final purpose is a normative one, where the classification identifies the normal circumstances under which a rule applies, thereby also clarifying those circumstances in which the rule does not apply. Sherwin points out that legal scholars vary in which purpose they find attractive and worth pursuing.
While I can appreciate that some legal scholars might not find the ‘formal’ classification of interest, I view it from a different perspective. First, any claim concerning the normative application of one rule instead of another rest entirely on the intuitive presumption that the rules are clearly different. This is a distinction that the first level can help to clarify. Similar points can be made for other relationships among rules. Second, focusing on the latter stage does not help to say specifically why one rule means what it does and has the consequences as intended; yet surely this is in virtue of the specific ‘content’ of the rule, which again is clarified by a thorough going analysis at the first stage. Third, if there is going to be any progress in applied artificial intelligence and law, it will require the analytical elements defined at the first stage. Fourth, as the study of Linguistics has shown, close scrutiny at the first stage can help to reveal very issues and problems that are fundamental to all higher stages. Fifth, providing even a small, clear sample of legal arguments analysed along other lines of the first stage can give the community of legal scholars a common ‘pool’ of legal arguments to fruitfully consider at the later stages; along these lines, it is notable how few concrete, detailed examples Sherwin’s paper discusses. Not surprisingly, some of the issues Sherwin raises about the purposes of different ‘levels’ of analysis also appear in the linguistic literature. In my view, though the first stage may not be interesting to most legal professionals, there are very good reasons why it should be.
Criteria of Taxonomy
Several different criteria which guide the taxonomy of legal rules are discussed.

      Intuitive similarity: whether researchers claim that two rules are subtypes of one another.
      Evolutionary history: the legal rule is traced in the history of the law.
      Formal classification: the logical relations among categories of the law.
      Function based: a function from the problem to a set of solutions.
      Reason based: the higher-level reasons that explain or justify a rule.

Sherwin criticises judgements based on intuitive similarity since the taxonomers may be relying on false generalisations rather than their own intuitions and that intuition can be arbitrary and without reason. This is also the sort of criticism leveled at large segment of linguistic research and which has been shown to be misleading. Of course, one must watch false classifications and try to provide a justification for classifying one element in one class and not another. One way to do this is, as in psycholinguistics, is to provide tests run over subjects. Another way is to refine the sorts of observations that lead to classifications. In general, all that we currently know about language, from dictionaries, to grammars, to inference rules is based on linguistic intuitions. Some, such as the rules of propositional logic, have been so fixed that they now seem to exist independent of any linguistic basis.
The issue here is somewhat related to classification by formal logical relations. It is unclear what Sherwin thinks logical relations are and how they are applied. What we do have more clarity on are some of the criteria for such a formal taxonomy: accounting for all legal materials, a strict hierarchy, consistent interpretation of classes, and no overlap of categories. This is but one way to consider a formal hierarchy; indeed, there is a separate and very interesting question about what formal model of classification best suits a legal taxonomy. Yet, this issue is not explored in the article.
The function based approach seems to have meta categories. For example, the rule above can be seen as a function from circumstances to a classification of a person as having committed an assault. However, this is not what appears to be intended in Sherwin’s discussion. Rather, there are meta-functional categories depending on higher level problems and solutions. The examples given are Law as a Grievance-Remedial Instrument and Law as an Administrative-Regulatory Instrument. For me, this is not quite as clear as Sherwin makes it appear.
The reason approach organises rules according to an even higher-level of the rule — the justification or explanation of the rule. Some of the examples are that a wrongful harm imposes an obligation for redress, deterring breaches of promises facilitate exchange, or promoting public safety. In my view, these are what people (e.g. Professor Bench-Capon) in AI and Law would call values which are promoted by the legal rule. Sherwin discusses several different ways that reason based classification is done: intended, attributed, and ideal rationales. In my view, the claimed differences are not all that clear or crucial to the classification. In some cases, the rationale of a legal rule is given by the adjudicator. However, where this is not so, the rationale is implicit and must be interpreted, which is to give the intended rationale. In other cases, legal researchers examine a body of law and provide rationales, which is the attributed rationale. In this sense, the intended and attributed rationales are related (both interpreted), but achieved by different methods (study of one case versus study of a body of cases and considerations about the overall purpose of the law). Finally, there are ideal rationales, which set out broad, ideal goals of the legal rule, which may or may not be ‘ideally’ achievable. In this, the difference between intended/attributed and ideal is whether the rationale is analysed out of cases (bottom-up) or provided legislatively (top-down). In the end, the result is similar — legal rules are classified with respect to some rationale. The general problem with any such rationale is just how it is systematically given and itself justified so as to be consistent and not to yield conflicting interpretations of the same legal rule. Finally, Sherwin seems to think that there is some intrinsic conflict or tension between formal classification and reason based classification. I don’t agree. Rather, the difference is in the properties and methods being employed to make the classification, which are not inherently in conflict. Likely, a mixed approach will yield the most insights.
Copyright © 2009 Adam Wyner

AI and Law contacts in Boston, MA

On a recent visit to Boston, Massachusetts USA, I had the opportunity to visit the Berkman Center for Internet and Law. It so happened that Kevin Ashley of the University of Pittsburgh was visiting the center for a meeting about legal document assembly. Kevin is a well-known expert in AI and Law, specialising in case based systems for legal reasoning that are geared towards helping law students learn to reason about the law. Kevin and I have met before and have a shared interest in ontologies and case based reasoning. We discussed research trends in legal case based reasoning, funding sources, and lines of collaborative research. I also found out that Richard Susskind, author of The End of Lawyers? was giving a talk at the Berkman center the same day, so I attended that talk, which was a distillation of his recent book. As it turned out Edwina Rissland of the University of Massachusetts at Amherst, another key figure in AI and Law (and Kevin’s former thesis advisor), was also at Susskind’s talk and also participating in the legal document assembly meeting. I’d not met her before, so it was a treat to have a brief chat. Finally, I met with Carole Hafner of Northeastern University, another central figure in legal case based reasoning. Carole was particularly helpful in drawing my attention to some of the earlier key articles on these topics by her and by Edwina. I meet with Carole every time I’m in the Boston area to get her views on AI and Law. In all, a very sociable and informative series of discussions.
Copyright © 2009 Adam Wyner