One example occurs in the case of Plessy v. Ferguson, 163 U.S. 537. Louisiana passed a statute that required blacks and whites to use “separate but equal” cars in trains. Plessy refused to comply, and he claimed that the Louisiana law violated the Fourteenth Amendment to the Constitution, which forbids states to deprive anyone of “the equal protection of the laws.”
In his argument for this claim, Plessy cited the precedent of Yick Wo v. Hopkins, 118 U.S. 356. That case was about an ordinance in San Fran- cisco that required a permit from the Board of Supervisors for any public laundry not operated in a brick or stone building. On its face, this ordinance was supposed simply to prevent fires. In practice, however, the Board of Supervisors granted permits to all but one of the non-Chinese applicants and denied permits to all the Chinese applicants. Because of this practice, Yick Wo claimed that the ordinance violated the equal protection clause. The Supreme Court agreed and declared the ordinance unconstitutional, at least insofar as it gave the city power to grant and refuse permits “without regard to the competency of the persons applying, or the propriety of the places selected for the carrying on of business.”
The argument from a precedent to a decision in a present case is often presented as an argument from analogy. In this form, the argument empha- sizes similarities between the cases, and then concludes that the decision in the present case should be the same as in the precedent. Plessy’s argument then appears to run something like this:
(1) The ordinance in Yick Wo was declared unconstitutional. (2) The ordinance in Yick Wo is similar to the statute in Plessy in several
(3) The statute in Plessy also ought to be declared unconstitutional.