The Supreme Court this week took another step back from its 1969 Miranda ruling, which requires police to notify criminal suspects of their right to remain silent when questioned. In a bizarre opinion by the court's conservative majority, the justices ruled 5-4 that unless a suspect explicitly invokes his right not to talk — that is, unless he talks to the police — he's not entitled to remain silent, and any statement he makes can be used against him in court.

This paradoxical interpretation of the law, as Justice Sonia Sotomayor pointed out in her first major dissent since joining the court, "turns Miranda upside down" and "bodes poorly for the fundamental principles that Miranda protects." In effect, it says to a suspect: You have the right to remain silent, but if you want to use it you'd better start talking.

The case involved a Michigan man, Van Chester Thompkins, whom police suspected of shooting another man to death outside a mall in 2000. When Mr. Thompkins was arrested a year later, police read him his Miranda rights, but he refused to sign a form acknowledging he understood them. He then remained silent through three hours of questioning until he was asked by an officer whether he thought God would forgive him "for shooting that boy down."

At that point, tears reportedly welled up in the suspect's eyes, and he expressed a belief in divine mercy. His affirmative response to the question was used as evidence at trial to convict him of first degree murder.

In his opinion for the majority, Justice Anthony M. Kennedy conceded that "some language in Miranda could be read to indicate that waivers [of the Miranda right] are difficult to establish absent an explicit written waiver or a formal, express oral statement." But, he concluded, "a suspect who has received and understood the Miranda warnings, and has not invoked his Miranda rights, waives the right to remain silent by making an uncoerced statement to the police." That is, if there's any ambiguity about whether a suspect intends to invoke his right to remain silent, police can keep asking questions as long as they like in hopes that he breaks down.

The court's ruling continued a recent trend of chipping away the protections afforded by the landmark Miranda decision, which sought to ensure criminal suspects are aware of their right to remain silent and to protect people suspected of crimes from incriminating themselves during prolonged interrogations. Earlier this year, the court ruled that police could vary the wording of the Miranda warning and that, after at least two weeks, any previous invocation of the right to remain silent was no longer valid.

This week's decision overturned a federal appeals court ruling that threw out Mr. Thompkins' murder conviction on the grounds his Miranda rights had been violated, but the principle involved transcends his actual guilt or innocence. What the court signaled this week was a determination to turn back the clock on a long-standing right that protects Americans from being coerced into confessions by lengthy interrogations. The right to remain silent should be just that, not an excuse for police to demand that suspects speak up.