In ordinary life, silence can be golden. Sensible and courteous people sometimes hold their tongues, especially on highly divisive questions. As the recent U.S. Supreme Court arguments over same-sex marriage attest, silence also plays a role in constitutional law.

Consider a little episode from Supreme Court history. In Poe v. Ullman, decided in 1961, the court was asked to strike down a Connecticut law forbidding the use of contraceptives. It declined to do so. But it also refused to rule that the law was constitutional.

Instead it said that the case wasn't "justiciable," in the technical sense that it wasn't appropriate for judicial review. The court's reason was that the law had hardly been enforced. The people who were challenging it (two married women and a male physician) didn't face the kind of immediate threat that would justify judicial intervention.