---
title: "Cooper v. Aaron — Definition & Meaning | Model Diplomat"
description: "Cooper v. Aaron (1958) affirmed that states must follow federal court rulings on the Constitution, crucial for Model UN and civil service studies."
url: "https://modeldiplomat.com/learn/glossary/cooper-v-aaron"
---

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Model Diplomat Research Team · Last reviewed June 22, 2026

TL;DR

- Cooper v.
- Aaron (1958) is the U.
- What constitutional principle does Cooper v. Aaron establish?
- How does Cooper v. Aaron differ from Marbury v. Madison?
- Why was Cooper v. Aaron signed by all nine Justices?

[Civil Service & Diplomatic Exams](https://modeldiplomat.com/learn/civil-services/glossary)Updated June 22, 2026

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## Positions at a glance

### Supporters

The Court unanimously rejected the delay, holding that the constitutional rights of the children "are not to be sacrificed or yielded to the violence and disorder" engineered by state officials. The opinion's enduring significance lies in its forceful articulation of judicial supremacy: it declared that Marbury v. Madison (1803) established the federal judiciary as "supreme in the exposition of the law of the Constitution," and that this principle "has ever since been respected by this Court and the Country as a permanent and indispensable feature of our constitutional system." The interpretation of the Fourteenth Amendment in Brown was therefore "the supreme law of the land," binding on state officials under Article VI's Supremacy Clause and the oath every legislator and executive officer swears to support the Constitution. State authorities could not nullify a federal constitutional ruling "openly and directly" or "by evasive schemes."

### Opponents

A distinctive feature of Cooper v. Aaron is that all nine Justices individually signed the opinion — an unprecedented gesture underscoring the Court's collective resolve against the doctrines of "interposition" and "nullification" then being revived across the segregationist South in resistance to Brown. The decision rejected the argument that the Governor and legislature of a state were not bound by Brown because they had not been parties to that litigation. Its reasoning has since anchored the modern understanding that the Supreme Court's constitutional interpretations bind coordinate branches and the states alike, a position later invoked in debates over "departmentalism" and decisions such as United States v. Nixon (1974) and City of Boerne v. Flores (1997).

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Example

In September 1957, President Dwight D. Eisenhower federalized the Arkansas National Guard and sent the 101st Airborne to escort the Little Rock Nine into Central High School, the confrontation that produced Cooper v. Aaron in 1958.

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