Abstract
An account of legal change in a common law system is developed. Legal change takes place incrementally through court decisions that are constrained by previous decisions in other courts. The assumption is that a court’s decision has to be consistent with the rules set out in earlier court decisions. However, the court is allowed to make add new distinctions and therefore make a different decision based on factors not present in the previous decision. Two formal models of this process are presented. The first model is based on refinement of (the set of factors taken into account in) the set of previous cases on which a decision is based. In the second model the focus is on a preference ordering on reasons. The court is allowed to supplement, but not to revise the preference ordering on reasons that can be inferred from previous cases. The two accounts turn out to be equivalent. A court can make a consistent decision even if the case base is not consistent; the important requirement is that no new inconsistencies should be added to the case base.
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Notes
- 1.
- 2.
The term “derogation” is often used to refer only to limitation of a norm, while its full removal is described as an “abrogation”. My terminology here follows that of Alchourrón and Makinson (1981).
- 3.
Alchourrón and Makinson (1981).
- 4.
Alchourrón and Makinson (1982).
- 5.
Alchourrón, Gärdenfors, and Makinson (1985).
- 6.
- 7.
- 8.
- 9.
Aleven (1997) has analyzed 147 cases from trade secrets law in terms of a factor hierarchy that includes 5 high-level issues, 11 intermediate-level concerns, and 26 base-level factors. The resulting knowledge base is used in an intelligent tutoring system for teaching elementary skills in legal argumentation, which has achieved results comparable to traditional methods of instruction in controlled studies; see Aleven and Ashley (1997).
- 10.
Both of the assumptions mentioned in this paragraph are discussed in Horty (2011).
- 11.
For the purpose of this paper, I simplify by assuming that the rule underlying a court’s decision is plain, ignoring the extensive literature on methods for determining the rule, or ratio decidendi, of a case. I will also assume that a case always contains a single rule, ignoring situations in which a judge might offer several rules for a decision, or in which a court reaches a decision by majority, with different judges offering different rules, or in which a judge might simply render a decision in a case without setting out any general rule at all.
- 12.
See Horty (2013).
- 13.
The most straightforward way in which the negation of the reason for the opposite decision would be entailed by the rule supporting the original, of course, is by being contained explicitly among the exceptions to that rule; but speaking more generally of entailment allows for other encodings as well.
- 14.
Makinson (2003).
- 15.
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Horty, J. (2014). Norm Change in the Common Law. In: Hansson, S. (eds) David Makinson on Classical Methods for Non-Classical Problems. Outstanding Contributions to Logic, vol 3. Springer, Dordrecht. https://doi.org/10.1007/978-94-007-7759-0_15
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