The U.S. Supreme Court this week heard oral arguments in two cases, United States v. Black and United States v. Weyhrauch, which offer the court a chance to limit a dangerous legal development. Traditionally, only those who freely choose to commit wrongful acts should be punished as criminals:“All are entitled to be informed as to what the state commands or forbids,” the court announced in 1939. But in recent decades, Congress passed thousands of vague and sweeping new criminal laws, and the court has done little to limit their reach. As a result, ordinary Americans are now criminally charged for inadvertently violating hopelessly vague statutes or for making the kinds of reasonable mistakes that we all sometimes make in our professional lives.The Supreme Court’s decision to hear Black and Weyhrauch is a hopeful sign that help may be on the way. Both cases concern the scope of the federal mail and wire fraud laws. Unlike traditional state fraud laws, these federal statutes criminalize deceitful conduct even if no one is actually deceived, even if no harm is actually caused, and even if the perpetrator received no benefit. These laws carry draconian penalties of up to 20 years in federal prison, and they apply broadly to any “scheme or artifice to defraud” that involves, even indirectly, use of the U.S. Postal Service, e-mail or telephone.Congress amended these already-broad statutes in 1988 to extend their reach to “the intangible right to honest services” owed, for example, by an employee to a company or by an elected official to a state government. The “honest services fraud” amendment has led federal courts to effectively rewrite — on the fly — the rules of engagement for almost all fiduciary relationships. The cost of this approach is that no one knows, anymore, just what those rules are.Black is a very technical case involving the adequacy of certain jury instructions, but Weyhrauch illustrates this danger well. Bruce Weyhrauch is a former Alaska state legislator who is in prison for federal mail fraud pending the outcome of his Supreme Court appeal. In 2006, Weyhrauch mailed his résumé to an oil and gas company called VECO Corp. in order to be considered for a job when his term in office was over. Weyhrauch was convicted of mail fraud for afterward voting on bills that affected VECO’s interests without disclosing his potential conflict of interest as an applicant for a future job with the company.