When the Constitutional Convention opened in Philadelphia, the very existence of a national judiciary was at issue. Delegates who favored state power argued that national laws could be enforced by state courts, whereas others, such as James Madison, foresaw the need for national judicial power. The “one supreme Court” created by the Constitution reflected ambivalence over the nature and scope of this power, and the Framers left to Congress significant discretion to determine the number of Supreme Court justices; the establishment, structure and jurisdiction of a lower federal judiciary; and the ability to make exceptions to the Court’s appellate jurisdiction.

While considering the question of a unitary executive, the delegates to the Constitutional Convention concluded that the judiciary was to be a legal rather than a political body. The Convention rejected the notion that the judicial branch should be any part of a proposed “council of revision,” which would have overseen the executive power to exercise a veto or to revise laws. Elbridge Gerry remarked that it was foreign to the nature of the judicial office to judge the policy of public measures. Rufus King argued that judges have to consider laws afresh, without having participated in making them.

Following the implicit command of the Constitution, Congress created a Supreme Court in the Judiciary Act of 1789 and set the number of justices at six. The Judiciary Act also established a subordinate federal judicial structure of several district and three circuit courts, each of the latter including two “riding” Supreme Court justices(reduced to one in 1793). The act also gave the Supreme Court appellate jurisdiction over federal questions growing out of litigation in state courts, thus cementing national power, while at the same time allowing state courts to make determinations on federal questions prior to final appeal. However, the act also confined the Supreme Court to questions of law rather than fact—an appellate limitation unusual for the time. This innovation was aimed at calming residual fears of national judicial power overturning local jury findings.

The first chief justice, John Jay, confirmed the intention of the Framers by insisting on the legal, rather than political, function of the Court and its justices. In Hayburn’s Case (1792), he wrote on circuit that Congress could assign only properly judicial tasks to the judiciary, thus upholding federal judges’ refusal to act as pensions claims adjudicators. Jay, speaking for the Court in a letter to President George Washington, also declined to render an advisory opinion Washington had requested concerning treaty interpretation.

In Marbury v. Madison (1803), Chief Justice John Marshall deftly reinforced both federal judicial power and the notion of the Court as a legal body. He did so by refusing to enter into a political dispute on the grounds that Congress could not constitutionally grant to the Court powers not authorized by the Constitution—in this case, original jurisdiction to issue a writ of mandamus. Underlying Marshall’s reasoning is the idea that the Constitution itself is a law to be interpreted by courts, and that courts cannot decide “questions, in their nature political,” or force coequal branches to perform political or discretionary acts.

The Federalist Congress reduced the number of justices sitting on the Supreme Court to five by the Judiciary Act of 1801, hoping to prevent incoming President Thomas Jefferson from appointing a justice when the sixth sitting justice retired. The 1801 act also established separate circuit court judgeships, obviating the need for Supreme Court justices to ride circuit. But such riding—and a Supreme Court of six—were quickly reinstituted in the Judiciary Act of 1802 under Jefferson, who was suspicious of national judicial power and desirous of keeping justices in expanded, so did the number of circuits and the number of Supreme Court justices to sit on them. The number of justices also expanded and contracted because of the politics of the Civil War and its aftermath, first from nine to ten to support President Abraham Lincoln’s war policies, then to seven to deprive President Andrew Johnson of several appointments. Since 1869, Congress has set the number of justices at nine, despite an unsuccessful effort by President Franklin D. Roosevelt to increase the Court’s size to suit his political agenda.

There has been a vigorous debate among scholars whether the vesting of judicial power in “one supreme Court” creates a “unitary judiciary” analogous to the idea of a “unitary executive” under Article II, Section 1, Clause 1 (Executive Vesting Clause). The “unitary judiciary” concept has two parts. The first is related to the Supreme Court’s jurisdiction and the extent of its ability to have the final word on all federal question matters. The second part relates to the Supreme Court’s supervisory authority over inferior courts.

Regarding the range of the Supreme Court’s jurisdiction, David Engdahl has argued that the use of the terms “supreme” and “inferior” in relation to courts, unlike the use of “inferior officers” in Article II, does not carry any connotation of hierarchy of authority. At the time of the founding, the terms “supreme” and “inferior” described the breadth of a tribunal’s jurisdiction, geographic scope, or some other status. A “supreme” court did not necessarily have appellate review or ultimate authority to have a final say concerning legal interpretations.

In contrast, Laurence Claus finds it important that the Framers used the lower-case “supreme” instead of the upper-case “Supreme” and that they included only one, instead of several supreme courts. The word “supreme,” he argues, is used as a description, not a title, signifying that the Court has the “last word” on all matters concerning “the judicial Power of the United States.” In the same way that the Constitution, federal law, and national treaties are “the supreme Law of the Land” taking precedence over state constitutions and state laws, the Supreme Court is “supreme” and its rulings take precedence over all “inferior” courts.

James Pfander also declares that the term “supreme” relates to the Supreme Court’s ability to review the decisions of courts “inferior” to it in the federal judicial hierarchy, but he asserts that “inferior” courts may include state courts that Congress may constitute as “inferior tribunals” under Article I, Section 8, Clause 9 (Inferior Courts). But Jason Mazzone notes that under the Judiciary Act of 1789, both inferior federal courts and, to some extent, state courts could reach decisions independent of and unappealable to the Supreme Court.

Steven Calabresi and Gary Lawson also argue, on the basis of the Constitution’s text and structure, that the Supreme Court has ultimate authority over any inferior courts. Significant is the fact that the word “inferior” is only used elsewhere in the Constitution in relation to “inferior officers,” and they conclude that the Supreme Court has authority over inferior courts in the same way the president has authority over inferior officers.

But Amy Barrett counters that the Constitution does not grant the Supreme Court nomination or appointment powers over inferior courts in the way that the president can nominate and appoint inferior officers in the executive branch. Moreover, the Constitution explicitly protects all judges with life tenure during period of good behavior, removing the possibility of Supreme Court judges removing or otherwise punishing inferior judges. Thus, “[i]nferior courts are capable of exercising judicial power wholly independently of the Supreme Court’s direction. They do not depend on the Supreme Court to give them the power, and the Supreme Court cannot take it away.”

The second part of the unitary judiciary concept relates to the supervisory authority of the Supreme Court—not only its ability to have appellate review of decisions of inferior courts, but also to issue procedural, evidentiary, and other types of rules that inferior courts must follow. Congress has granted the Supreme Court some rule-making authority by statute, but the Supreme Court has issued supervisory rules on inferior courts outside of these statutory bounds on the basis of its “inherent authority” that stems from “the judicial Power.” The issue and the history are complex. Scholars similarly argue whether the Court has either explicit or implicit power to make rules for lower federal courts, and to what extent Congress, under the Necessary and Proper Clause, can displace the Supreme Court in making such procedural or evidentiary rules.