⚡ 10-Second Rule
When a valid federal law and a state law truly clash, the federal law wins and the state law stops working.
🧒 ELI-10 Scene
Mom leaves written rules for the babysitter, Priya. Mom's notes always beat Priya's rules when they clash. Sometimes Mom writes it plainly: "Bedtime is my call alone — no babysitter bedtime rules." Then Priya's bedtime ideas are out, period. Sometimes Mom writes pages of detailed rules about dinner, covering every single food. That thoroughness shows dinner is entirely Mom's territory. Sometimes the rules collide head-on: Priya says "dessert first," Mom says "dessert never." Priya loses. But if Mom says "brush teeth at least one minute" and Priya says "two minutes," the kids can obey both. And for things babysitters have always handled, assume Priya's rules survive unless Mom clearly canceled them.
⚖️ Actual Rule
The Supremacy Clause, Article VI, Clause 2, provides: "This Constitution, and the Laws of the United States which shall be made in Pursuance thereof; and all Treaties made, or which shall be made, under the Authority of the United States, shall be the supreme Law of the Land; and the Judges in every State shall be bound thereby, any Thing in the Constitution or Laws of any State to the Contrary notwithstanding." Preemption takes two forms. Express preemption exists where a federal statute explicitly displaces state law. Implied preemption has three branches: (1) field preemption, where the federal regulatory scheme is so pervasive that Congress left no room for state supplementation (Rice v. Santa Fe Elevator Corp., 331 U.S. 218 (1947); Arizona v. United States, 567 U.S. 387 (2012)); (2) conflict preemption by impossibility, where compliance with both federal and state law is a physical impossibility (Florida Lime & Avocado Growers, Inc. v. Paul, 373 U.S. 132 (1963)); and (3) obstacle preemption, where state law "stands as an obstacle to the accomplishment and execution of the full purposes and objectives of Congress" (Hines v. Davidowitz, 312 U.S. 52 (1941)). In fields traditionally occupied by the states, courts presume "the historic police powers of the States were not to be superseded by the Federal Act unless that was the clear and manifest purpose of Congress" (Rice).
ELI-10 translation: federal law erases state law only when Congress says so, fills the whole field, or the two rules cannot live together.
🔍 Ask These Questions
- Is there a valid federal law on point? (Federal law only wins if Congress had the power to pass it.)
- Does the statute contain an express preemption clause — or a savings clause preserving state law? (Read Congress's own words first — eviction notice or welcome mat?)
- Field: is the federal scheme so pervasive that Congress left no room for states? (Did the federal rules fill every shelf in the cabinet?)
- Impossibility: can a person obey both laws at once? (If following one rule forces breaking the other, the state rule falls.)
- Obstacle: does the state law frustrate what Congress was trying to accomplish? (A state roadblock on the federal path gets cleared away.)
- Is this a traditional state domain — health, safety, family, land? (Assume state rules survive there unless Congress spoke clearly.)
⚠️ Bar Trap
Exam language: Examiners suggest that any federal regulation in an area automatically displaces state law, offering choices like "invalid, because the federal government has regulated this field." Mere overlap is not preemption: where the federal statute sets a floor — a minimum standard — a stricter state requirement usually survives, because a party can comply with both and Congress's purpose is not obstructed.
ELI-10: Federal rules and state rules can share a room. The state rule leaves only if Congress kicked it out, hogged all the space, or the two rules truly fight.
🧪 Question
A federal statute establishes minimum labeling requirements for bottled spring water, requiring each label to disclose the water's source and bottling date. The statute provides: "Nothing in this Act shall be construed to limit the authority of any State to impose additional labeling requirements for bottled water sold within its borders." The state of Meridia subsequently enacts a law requiring bottled-water labels sold in Meridia to also disclose the water's mineral content. A national bottler, which sells identical products in all fifty states, sues to enjoin the Meridia law, arguing it is preempted.
Is the Meridia law preempted?
(A) Yes, because Congress has occupied the field of bottled-water labeling by enacting comprehensive federal requirements. (B) Yes, because the Supremacy Clause makes any federal regulation of a subject exclusive of state regulation. (C) No, because the bottler can comply with both laws and Congress expressly preserved state authority to add requirements. (D) No, because product labeling is a matter reserved exclusively to the states under the Tenth Amendment.
Answer: (C). The federal statute sets a floor, and its savings clause is the clearest possible evidence that Congress did not intend to occupy the field. A bottler can print source, date, and mineral content on one label, so compliance with both is possible, and the state addition obstructs no federal purpose.
💡 Why the Wrong Answers Are Wrong
- (A) finds field preemption despite a savings clause expressly inviting state supplementation — the opposite of pervasive exclusivity.
- (B) overstates the Supremacy Clause; supremacy resolves actual conflicts, it does not make every federal statute exclusive.
- (D) inverts the error — labeling is not exclusively state territory, since Congress can plainly regulate goods sold in interstate commerce.
- ELI-10: The misconception is thinking one federal rule empties the whole shelf. Extra state rules stack fine on top of a federal minimum.
