A Rule of Three

By custom, the votes of four Justices are required to grant certiorari. Nowadays the Court is often criticized for taking too few cases. This Term the Court will decide fewer than sixty cases with signed opinions, which is the lowest level since the 1860s. 

Suppose you think that the Court is taking too few cases. One option would be to urge the Justices to take more cases. Another would be for Congress to expand the Court's mandatory jurisdiction. But there is a third possibility. The Court's custom could be changed to allow a certiorari grant by only three Justices. This reform would require no action by Congress and could be done tomorrow.

What's so special about the Rule of Four? I don't know how the Justices settled on this standard back in the 1920s. If there is a good article on that, feel free to email and tell me. Maybe four Justices was the correct custom back then but is not a hundred years later.