A robust 8-1 majority of the Supreme Court ruled today that, contrary to folk belief, ignorance of the law is a perfectly good excuse—as long as it's a cop who's claiming ignorance. The case, Heien v. North Carolina, dealt with a car owner who ended up charged with cocaine trafficking after a police officer, who thought the driver looked "nervous," followed the car and stopped it because it had only one working brake light.

The North Carolina state court of appeals had concluded that because state law says a car must have "a stop lamp," singular, it's not illegal to operate a car that's down to one functioning brake light. But the Supreme Court decided that even though the car was legal, the arresting officer's "mistaken understanding of the law was reasonable."

"To be reasonable is not to be perfect, and so the Fourth Amendment allows for some mistakes on the part of government officials,," the majority wrote.

The majority explained that this ruling, upholding an incorrect act of law enforcement, will not encourage the police to enforce laws incorrectly:

An officer may, however, also be suddenly confronted with a situation requiring application of an unclear statute. This Court's holding does not discourage officers from learning the law. Because the Fourth Amendment tolerates only objectively reasonable mistakes, cf. Whren v. United States, 517 U. S. 806, 813, an officer can gain no advantage through poor study. Finally, while the maxim "Ignorance of the law is no excuse" correctly implies that the State cannot impose punishment based on a mistake of law, it does not mean a reasonable mistake of law cannot justify an investigatory stop.

Here was the Court's trademark, cross-partisan detachment from ordinary American experience on full display. Surely the cops would never pull anyone over on bogus grounds, out of malice, and blame it a law that doesn't apply.

As for the problem of how officers might grapple with suddenly encountering a legally confusing situation, it's hard to imagine a less esoteric law-enforcement question than whether or not the police are allowed to stop your car for having some of its brake lights out. Cops make, or don't make, such stops every day.

The mystery is how North Carolina's law had gone unclarified before this. But as the lone dissenter, Sonia Sotomayor, argued, the majority's line of reasoning effectively moots future questions about what such a law would mean:

One wonders how a citizen seeking to be law-abiding and to structure his or her behavior to avoid these invasive, frightening, and humiliating encounters could do so.

In addition to these human consequences—including those for communities and for their relationships with the police—permitting mistakes of law to justify seizures has the perverse effect of preventing or delaying the clarification of the law. Under such an approach, courts need not interpret statutory language but can instead simply decide whether an officer's interpretation was reasonable. Indeed, had this very case arisen after the North Carolina Supreme Court announced its rule, the North Carolina Court of Appeals would not have had the occasion to interpret the statute at issue.

"One is left to wonder," Sotomayor wrote, "...why an innocent citizen should be made to shoulder the burden of being seized whenever the law may be susceptible to an interpretive question."

[Image via AP]