The "separate but equal" principle came from the Supreme Court's ruling in the notorious case of Plessy v. Ferguson (1896). The plaintiff in this case objected to the way in which African Americans were forced to occupy a separate carriage in a passenger train. Trains were just one of many facilities segregated according to race under the so-called Jim Crow laws then in operation throughout the South. In his submission to the court, Plessy agreed that such laws constituted a violation of his civil rights under the Fourteenth Amendment to the Constitution.
In ruling against Homer Plessy, the court held that a law that implies merely a legal distinction between the races was not unconstitutional. According to the court, the Fourteenth Amendment only applied to political rights—such as voting and jury service—and not social rights, such as sitting in the train carriage of your choice.
The court further ruled that separate facilities were perfectly constitutional so long as they were of equal quality. In other words, they had to be separate, but equal. In actual fact, however, many segregated facilities were anything but equal. Public schools for African Americans were much worse than those provided for white students, for example. But the court in Plessy overlooked the substantive differences between separate facilities and held that the provision of such facilities on the basis of race did not in itself confer a badge of inferiority on African Americans.
It would be just over half a century before this pernicious doctrine was finally overturned in the landmark civil rights case of Brown v. Board of Education (1954).