Yick Wo

This argument is not very good as it stands, so we need to add some sup- pressed premises.

The first step is to construct a list of the respects in which the cases are similar. That is not always easy. When we are evaluating someone else’s ar- gument, we can focus on the similarities that he or she mentions. But when we are constructing our own legal arguments, we have to be more creative; we have to formulate the respects in which the cases are supposed to be sim- ilar. Some similarities do not matter: It is clearly irrelevant that the laws in Yick Wo and Plessy both contain more than ten words or that both apply to large cities. This much is assumed by both sides in the case, and legal rea- soning would be impossible without assuming that many such similarities are irrelevant. Likewise, not all differences matter: It is not important, even if true, that Yick Wo was married and over fifty years old, but Plessy was not. To discount or distinguish the precedent, one must show that some dif- ference between Yick Wo and Plessy is important enough to justify reaching different decisions in these cases. The central question, then, asks which fac- tors—similarities and differences—do matter. In general, the answer is that a factor is relevant when it is needed to justify the decision in the precedent. These factors are often called the ratio decidendi—the reason for the decision.

Incorporating the doctrine of precedents as a suppressed premise, the argument from Yick Wo to Plessy can now be reconstructed as follows:

(1) The ordinance in Yick Wo was declared unconstitutional. (2) The ordinance in Yick Wo is similar to the statute in Plessy in several

respects (A, B, C, D, and so on). (3) These are the features that justified declaring the ordinance in Yick Wo unconstitutional. (4) There are no important enough differences between Yick Wo and Plessy to justify distinguishing the precedent.

(5) Yick Wo ought not to be overturned. (6) If a precedent is similar to a present case in the respects that

justified the decision in the precedent, and if the precedent ought not to be either overturned or distinguished, then the present case ought to be decided in the same way as the precedent.

(7) The statute in Plessy ought to be declared unconstitutional.

This argument is now valid, but validity does not get us very far. We still need to know whether its premises are true.