It is his to interpret whose it is to enact.

Explanation

(English-origin maxim.) The authority to interpret a law belongs to the body that enacted it. In the American system, the People enacted the Constitution — and the judiciary's duty under judicial review (Marbury v. Madison) is to test statutes against that supreme enactment. No legislature may authoritatively interpret the Constitution to expand its own power; that interpretation belongs to the People and the courts they established to guard the instrument.

Where this applies

• A city council passes an ordinance, and when someone challenges it, the mayor tries to reinterpret the ordinance to mean something it never said — but the council that wrote it gets to say what it means, not the mayor.
• Congress passes a tax law, and the IRS issues a regulation that stretches the statute way beyond what Congress intended — taxpayers argue the agency can't rewrite a law it didn't enact.
• A homeowners association board tries to reinterpret a covenant that the original members drafted, giving the board powers the members never intended to grant.