Setting the number of justices on the United States Supreme Court and judges on the New York State Court of Appeals
Response to an inquiry from a NYPPL reader
The short answer to your question concerning determining the number of justices on the United States Supreme Court is the number of justices is set by Act of Congress as the Constitution of the United States does not provide for the number of justices sitting on the Court.
§1 of the Judiciary Act of 1789 provided that "That the supreme court of the United States shall consist of a chief justice and five associate justices, any four of whom shall be a quorum", i.e., six justices.
From time to time the number of justices on the Supreme Court has been modified by Acts of Congress to reflect the growth of the United States and the increasing number of judicial circuits.
For example, the "Seventh Circuit Act of 1807" statutorily increased the size of the Court from six Justices to seven.
Subsequently the number of justices was increased to 9 in 1837 and then to 10 in 1863. In 1869, however, the Circuit Judges Act set the number of justices of the Supreme Court back to 9, and it has since remained 9 notwithstanding former President Franklin D. Roosevelt's attempt to increase the number of justices to "not to exceed 15."
In contrast, §2 of Article VI - Judiciary - of the Constitution of the State of New York, in pertinent part, provides:
a. The court of appeals is continued. It shall consist of the chief judge and the six elected associate judges now in office, who shall hold their offices until the expiration of their respective terms, and their successors, and such justices of the supreme court as may be designated for service in said court as hereinafter provided. The official terms of the chief judge and the six associate judges shall be fourteen years.
Five members of the court shall constitute a quorum, and the concurrence of four shall be necessary to a decision; but no more than seven judges shall sit in any case. In case of the temporary absence or inability to act of any judge of the court of appeals, the court may designate any justice of the supreme court to serve as associate judge of the court during such absence or inability to act. The court shall have power to appoint and to remove its clerk. The powers and jurisdiction of the court shall not be suspended for want of appointment when the number of judges is sufficient to constitute a quorum.
b. Whenever and as often as the court of appeals shall certify to the governor that the court is unable, by reason of the accumulation of causes pending therein, to hear and dispose of the same with reasonable speed, the governor shall designate such number of justices of the supreme court as may be so certified to be necessary, but not more than four, to serve as associate judges of the court of appeals.