Too Vague to Be Constitutional Two indecipherable criminal laws passed in the 1980s now face scrutiny at the Supreme Court.

The legal philosopher Lon Fuller once invented an earnest monarch named Rex who discovered many wrong ways to make law. First, Rex wrote a detailed code of laws, but, to avoid confusing the public, kept it secret. “To Rex’s surprise this sensible plan was deeply resented by his subjects. They declared it was very unpleasant to have one’s case decided by rules when there was no way of knowing what those rules were,” Fuller wrote. So Rex refined his code even further and made it public. But its detail and precision made it “a masterpiece of obscurity.” Soon “a picket appeared before the royal palace carrying a sign that read, ‘How can anybody follow a rule that nobody can understand?’”

Next week the Supreme Court will look at cases in which two criminal defendants make similar pleas. On Monday, a violent neo-Nazi contends that he is facing 15 years in prison under a law that not only he but some of the most learned judges in the country find incomprehensible; the next day, a dealer in “designer drugs,” claims that he is facing prison under a law so complex that its prohibitions are effectively ecret from anyone except skilled chemists.

The neo-Nazi, Samuel Johnson, faces a 15-year minimum sentence under theArmed Career Criminal Act. ACCA provides that any person convicted in federal court of a firearms offense will receive a minimum 15-year sentence if he or she has previously been convicted three times in state or federal court of “a violent felony or a serious drug offense.” As originally passed in 1984, the Act limited the “violent felonies” to crimes in which force was actually used or threatened, or to any robbery or burglary; two years later, Congress made the law even “tougher.” It now specifies that any offense is a “violent felony” if it “is burglary, arson, or extortion, involves use of explosives, or otherwise involves conduct that presents a serious potential risk of physical injury to another.”

The last part is called the “residual clause.” With admirable restraint, Justice Antonin Scalia wrote a decade ago that the clause “is, to put it mildly, not a model of clarity.” In fact, it has tied the federal courts in knots. In the past decade, the Supreme Court has had to settle disputes over whether “violent felony” applies to attempted burglary (no), driving under the influence (no), failure to report for incarceration (no), and intentional flight from law enforcement in a motor vehicle (yes). But confusion persists, with different standards prevailing in different appellate-court jurisdictions. For example, in the Fifth Circuit, reckless assault is “violent,” while in the Sixth, reckless homicide is not. In the Fourth Circuit, battery of a police officer is not “violent,” in the Tenth it is. In the Fifth, Sixth, Seventh, and Tenth Circuits, fleeing law enforcement on foot is “violent”; in the Eighth, Ninth, and Eleventh it is not.

As these crazy results piled up, the Court’s cries for help have grown louder. In 2006, Scalia, dissenting in the attempted burglary case, argued that the Act “violates ... the constitutional prohibition against vague criminal laws.” In 2008, Justice Alito wrote that “only Congress can rescue the federal courts from the mire into which ACCA’s draftsmanship” has thrust it. In 2011, Scalia again urged the Court to admit that ACCA “is a drafting failure and declare it void for vagueness.”

Against this backdrop, Johnson v. United States reached the Court last November. As the head of something called the Aryan Liberation Movement, Johnson boasted to FBI informants that he had, and planned to use, napalm, explosives, an AK-47, 1,100 rounds of ammunition, and silencers. He was convicted of being a “felon in possession” of firearms and ammunition; the district court promoted him to career status because of two previous convictions of robbery and one of possession of a short-barrel (“sawed-off”) shotgun. Before the Court, his federal defender argued that mere “possession” of an illegal weapon was not “purposeful, violent, and aggressive” enough to qualify as a “violent felony.” She asked the Court to add short-barrel possession to the list of felonies that aren’t “violent”; if it did so, she said, “this Court need not get into whether [ACCA] is unconstitutionally vague and the baby should go out with the bath water.”