... We are so used to the Court deciding a case by a divided vote—with a majority opinion, one or more concurrences, and one or more dissents (there are some cases in which all nine justices have written opinions)—that we forget that until the 1940s over 90 percent of the cases decided each term, sometimes as many as 200 cases, were decided unanimously. Much of the credit for that goes to two early chief justices, Oliver Ellsworth and John Marshall. Between them they did away with the English practice of seriatim, in which each member of the court wrote an opinion. While one might tally the votes to see who had won, it proved far more difficult to determine the jurisprudential theory behind the opinion. Marshall especially believed that if the Court spoke in one voice, its decisions would have greater influence—an idea that many judges on both the federal and state benches still share.

At least until the late 1920s, unanimity proved fairly easy because a majority of the cases before the court had little significance to anyone other than the litigants. Today, nearly all of these cases would be heard by lower—much lower—state courts. As Justice Louis Brandeis said in 1923, “It is more important that these cases be decided than that they be decided right.” But there were dissents that proved more influential than the majority decisions. In a series of cases challenging the emerging Jim Crow regime in the former Confederate states, especially the infamous decision in Plessy v. Ferguson (1896) upholding the doctrine of “separate but equal,” Justice John Marshall Harlan dissented over and over again, famously declaring, “Our Constitution is color-blind, and neither knows nor tolerates classes among its citizens.” It took over six decades before Harlan’s view became the law of the land, starting with Brown v. Board of Education in 1954. (In an interesting twist, conservatives on the Court led by the Chief Justice have used Harlan’s words as a rationale to oppose affirmative action as well as efforts by various school districts to prevent re-segregation.)

In the 1920s, Oliver Wendell Holmes Jr. and Brandeis frequently dissented together. The theories of these two men, especially regarding the First Amendment’s protection of speech, eventually became the standard by which modern courts evaluate free speech questions. Of especial note is the Brandeis opinion in Whitney v. California (1927), which although technically a concurrence, has been hailed by many scholars as the greatest dissent ever written. In it, Brandeis eloquently explained why free speech mattered, not as the abstraction of Holmes’s often cited free market of ideas, but as an integral part of the democratic process by which citizens could learn all sides of important policy discussions. It took nearly four decades before the Court fully adopted Brandeis’s view, but he understood that such might be the case. “My faith in time,” he said, “is great.”...