Nine justices sit on the Supreme Court, and to most people that number feels fixed, almost carved in stone. It is easy to assume the founders wrote it into the Constitution and locked it there forever. They did not. The Constitution creates the Court but never says how many justices should serve on it. That choice was left to Congress, which sets the number by ordinary law. Over the country's history that number has moved up and down more than once.
The story starts in 1789, the same year the new government took shape. The first Congress passed the Judiciary Act and set the Court at six members, a chief justice and five others. Six may sound odd today, but the Court had a lighter load then and rode circuit across the country. In those early years justices spent much of their time hearing cases in the regions, not just in the capital. The size fit the work of the day. It was a practical call, not a grand rule.
From there the number bounced around for decades. In 1807 Congress raised it to seven as the country added new territory and courts. In 1837 it grew to nine to match a rising number of judicial circuits out west. During the Civil War, in 1863, it climbed to ten. Each change tracked the growth of the nation and the caseload the justices had to carry. The point is that the size was a moving target for most of the 1800s.
The number also moved for reasons that had little to do with caseload. In 1866 Congress shrank the Court from ten toward seven, in part to deny President Andrew Johnson the chance to fill seats. Johnson was at war with Congress over how to rebuild the South, and the size of the Court became a bargaining chip in that fight. A few years later, with a new president in office, the mood changed again. This was one of the clearest cases of the Court's size being shaped by raw politics. It showed how tightly the question could tie to the mood of the moment.
The number we know today arrived in 1869. That year Congress passed a new Judiciary Act and set the Court at nine members, where it has stayed ever since. Nine matched the number of judicial circuits at the time, so there was a tidy logic to it. What began as a practical fit slowly hardened into tradition. More than a century and a half later, nine feels like the natural size even though no law of nature requires it. Custom, not the Constitution, is what holds it in place.
The most famous attempt to change the number came in 1937. President Franklin Roosevelt was frustrated that the Court kept striking down parts of his New Deal. He proposed a plan that would let him add a justice for each one over the age of seventy, which could have grown the Court to as many as fifteen. Critics called it court packing and warned it would bend the Court to the president's will. Even members of his own party balked, and the plan died in Congress. The fight left a lasting wariness about touching the number.
Because the size sits in statute, changing it does not take a constitutional amendment. Congress could pass a law to add or remove seats with a simple majority and a president's signature. That is a far lower bar than the long process an amendment demands. The reason the number holds is not legal difficulty but political caution and long habit. Both parties have generally treated nine as settled ground. Proposals to change it surface from time to time, but none has passed since 1869.
So the short answer is that nine is a choice, not a command. Congress set the number, moved it several times, and landed on nine in 1869 for reasons of circuits and convenience. It has stayed there through custom and a shared reluctance to reopen the question. Knowing that history makes the debates you hear today far easier to follow. The number is fixed by tradition and law, and either could shift if the political will ever lined up. For now, nine remains the number, held in place more by habit than by the founding document.
