Legal cases are decided by precedent, but few precedents make thecase at bar res judicata.Instead, analogical reasoning is used, together with canons of statutoryinterpretation and theories of constitutional jurisprudence. This paperprovides a model and algorithm for analogical reasoning in the legalcontext.

The model is best explained by the example used throughout thepaper, the rule that vehicles are not allowed in a public park. How dowe reason analogically that horses are not allowed in a public park? Theanswer given by the paper is to look at the properties of a vehicle thatform the ground for the rule (being larger than a human being and beingmobile, hence being dangerous) and checking the case being considered tosee whether the properties and relations that form the ground of therule apply there, too. In the case of a horse, although it is not avehicle, it is large and mobile, hence potentially dangerous, so weconclude that it is not permitted in a public park. Since the methodseeks the reason for the rule and abstracts it out, it is calledgoal-dependent abstraction. To do this, a higher-level entity ispostulated, whose properties include all those known to be covered bythe rule. The new entity is then checked to see whether it is aninstance of the postulated entity. If it has the properties, it is takento be an instance of the higher-level entity, and the properties areassumed to have been inherited. The authors call this process“generalization and deduction.”

In addition to having an annoying number of missing articles,misplaced modifiers, and failures of agreement, the paper uses anordinance rather than cases for analogical reasoning, a practice thatmakes little sense unless the legislature is always perfectlyconsistent. Thus, buses and maintenance vehicles may be allowed, despitethe ground, and horses may have been overlooked, despite the ground.There is also an assumption that laws do not originate from pressure byinterest groups but from well-defined, broadly applicable reasons. Sucha system could not, for example, distinguish licensed vehicles fromunlicensed vehicles if the purpose of the licensing system were to raisefunds and limit competition. In summary, the paper’s methodology isappropriate for judicial reasoning from prior cases, but fails in itsapparent application as a means of interpreting ordinances andstatutes.