How many justices must agree to grant a writ of certiorari?

The requirement for a majority of four justices to agree in order to grant a writ of certiorari is grounded in the practice of the Supreme Court. A writ of certiorari is a formal request to the Supreme Court to review a lower court's decision. The rationale behind needing four justices is often referred to as the "rule of four." This rule ensures that not just a simple majority is needed to hear a case, but rather that a substantial minority feels strongly enough about the importance of the case to warrant the Court's attention. This mechanism serves to protect minority viewpoints within the Court and encourages thorough consideration of which cases are worthy of review, as the Supreme Court has a limited capacity to hear cases.

The number reflects a balance between allowing access to the Court while managing its docket effectively. In contrast, a simple majority of justices would risk ignoring significant legal issues that may arise in only a few cases. This context clarifies why the answer is indeed that four justices must agree to grant certiorari.