If Harlan is right, the Court’s argument has a false premise, so the statute in Plessy should have been found unconstitutional even if the Court was right about what was necessary to find a law unconstitutional.
We can summarize this discussion by listing various ways in which argu- ments from precedents can fail:
1. The precedent and the present case might not truly resemble each other in the ways that the argument claims.
2. The respects in which the cases resemble each other might not be important enough to justify the same decision in the present case.
3. The precedent and the present case might also differ from each other in important respects that justify distinguishing the precedent.
4. The precedent might be mistaken or immoral enough to be overturned.
5. There might be other, stronger precedents that conflict with the precedent in the argument.
Whenever you evaluate or present any argument from a precedent, you need to ask whether the argument fails in any of these ways.