How Government Works

The Supremacy Clause

Have you ever wondered what happens when a federal law says one thing and a state law says another? The answer to the question lies in Article 6, Paragraph 2, of the United States Constitution, which is commonly known as the “Supremacy Clause.” Under the Supremacy Clause, federal laws, which apply to the entire country, are supreme over state laws, which apply only to particular states (like Arizona).

The Supremacy Clause

Article 6, Paragraph 2 of the United States Constitution says the following:

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.

What the Supremacy Clause basically says, in plain language, is that the United States Constitution and federal law (including foreign treaties) are supreme over state constitutions and state law. This is a very important part of the American political structure because it ensures that, where the United States Constitution grants power to the national government, laws enacted by that national government outrank – or take precedence – over laws enacted by state governments. If the United States Constitution did not include the Supremacy Clause, the various states and the federal government probably would be arguing constantly over whose laws should apply in every situation. The federal government also would find it much harder to exercise its own constitutional powers in the overall national interest. Without the Supremacy Clause, the United States of America might not be so “united.”

The doctrine of preemption

Whenever a state and a federal law disagree, the federal law will prevail. But how is it determined in the first place whether the federal law and a state law are in conflict? The determination is made through the use of a legal principle known as the “doctrine of preemption.”

In its ordinary use, to “preempt” (or “pre-empt”) means to “take action in order to prevent an expected event from happening.” In the constitutional context, to “preempt” has a similar meaning: Whenever a federal law exists in an area in which the United States Constitution grants authority to the national Congress under the “enumerated powers,” that federal law prevents any state law – whether it comes from the state’s constitution, the state’s legislature, a state court, or one of the state’s administrative agencies – from having effect. The state law is “preempted.”

Under the American federal system of government, all powers not expressly granted by the United States Constitution to the national Congress are reserved to the states. Consistent with this arrangement, what the doctrine of preemption says is that unless evidence exists that the national Congress intended that a federal law would “preempt” a state law, the presumption is  that Congress had no such intention, and the state law will stand.

So what counts as evidence of Congressional intent to preempt a state law? Congress can show its intent to preempt a state law in two ways: (1) by saying so “expressly” (directly) in the federal statute (which is known as “express preemption”) or (2) by saying so “impliedly” (indirectly) through the structure or purpose of the federal statute (which is known as “implied preemption”). Implied preemption itself takes two forms: If the structure or purpose of the federal statute would make it impossible to comply with the federal law and a state law simultaneously, then Congress is presumed to have intended to preempt the state law. This is known as “conflict preemption.” If the structure or purpose of the federal statute is so extensive that the regulations it creates will occupy an entire field of law, then Congress is presumed to have intended to preempt the state law. This is known as “field preemption.”

This website has been prepared for general information purposes only. The information on this website is not legal advice. Legal advice is dependent upon the specific circumstances of each situation. Also, the law may vary from state-to-state or county-to-county, so that some information in this website may not be correct for your situation. Finally, the information contained on this website is not guaranteed to be up to date. Therefore, the information contained in this website cannot replace the advice of competent legal counsel licensed in your jurisdiction.

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