The Rule of Four

The rule of four is not found in the Constitution, any statute, or the Court's written rules. It became known when Justices described it to Congress while lobbying for the Judiciary Act of 1925, which gave the Court broad discretion to choose its cases, as an assurance that the new power would not be used to shut out cases a substantial minority thought deserving. Under the practice, a petition for certiorari is granted if four Justices vote for it, even though five votes are needed to decide the case.

Votes on petitions are taken at the Justices' private conferences and are generally not announced, though individual Justices sometimes note their dissent from a denial. The Court has related customs: it often holds petitions that raise the same issue as a pending case and then sends them back to lower courts in light of the decision, and five votes are needed to grant a stay or an emergency injunction. Occasionally the Court grants review and later dismisses the case as improvidently granted, which can happen when a majority concludes it should not have taken the case.

Defenders say the rule of four protects the Court's legitimacy by ensuring that significant questions supported by a substantial minority get a hearing, and that it guards against the majority ignoring important cases. Some Justices and scholars have questioned whether a minority should be able to force the full Court to decide a case, especially when the majority would prefer to let an issue develop further in the lower courts, and others note that strategic voting can keep a case off the docket when a minority fears the likely outcome.