The key words in Justice Anthony Kennedy's Guantanamo opinion do not involve the history of habeas corpus, the territorial status of Guantanamo Bay or the accountability of the executive branch to the rule of law. They appear on the opinion's penultimate page and are unlikely to attract much attention amid the chatter the decision has already generated. "(O)ur opinion does not address the content of the law that governs petitioners' detention," Kennedy wrote. "That is a matter yet to be determined."

Yes, habeas corpus has been grandly re-established at Guantanamo. But, as the court majority made clear in this brief passage, that does not mean the government is holding a single person illegally at the base. Nor did the court have a whole lot to say about what procedures the government needs to use to determine whom to detain. Most important, it didn't require that anyone at the base walk free.

The result is that 6 1/2 years after the Sept. 11 attacks, America still faces many of the fundamental questions about detentions that it faced the day the military brought its first captives to Cuba.

It's long past time to answer them. Indeed, Congress and the executive branch — whether the Bush administration or its successor — desperately need to enact a comprehensive legislative solution to the problem of detentions in the war against terrorism, both clearly defining "the content of the law" and creating appropriate procedures for making those judgments.

The Guantanamo population has never been a monolith. Some detainees the military has held at the base are extremely dangerous — proud military enemies of this country whom no society with an instinct for self-preservation would set free. One, for example, told a review panel: "I do pose a threat to the United States and its allies. I admit to you that it is my honor to be an enemy of the United States. I'm a Muslim jihadist." Other detainees admit facts that clearly render them subject to detention under the laws of war, though they may not be al-Qaida or Taliban terrorists.

The majority of detainees, meanwhile, either deny the allegations against them — with varying degrees of plausibility — or choose not to address them in the primitive review mechanisms the government has set up. These detainees often present complex and murky issues of fact that any adjudicatory system has to resolve.

Guantanamo also houses a substantial group of detainees whom the government has long since cleared for release or transfer but whom it cannot send home for fear they might be tortured and whom other countries are not itching to take in. Some of them pose little or no threat to the United States. Additionally, the base houses a substantial group the military intends eventually to put on trial for war crimes.

The current system — at least in public — labels all these groups "enemy combatants." But they present different problems. What's more, because the government's review processes are so anemic, the Supreme Court showed those processes little deference, and one can expect that lower courts, in the habeas cases this decision will bring back to life, will show little more to the detention decisions that resulted. A better system would cause courts to show more respect when habeas review rolls around.

A reasonable system would do as much adjudication as possible in public, creating for each detainee a rigorous set of factual findings and a record evaluating the decision to detain. For detainees of the type held at Guantanamo, whom the laws of war fit uncomfortably, the detention decision ought not to reside in the military but in a civilian federal court, assigned by statute to assess whether each detainee meets a legislatively prescribed standard.

In this proceeding, detainees should have real rights, starting with representation by competent counsel, cleared to see all evidence — even classified evidence — against their clients. Detainees themselves need a more detailed summary of the evidence against them and a more meaningful opportunity to present evidence of their own. Judicial supervision of these decisions must persist as long as the detentions persist, ensuring that the detentions are humane and remain necessary.

Congress, in short, needs to design a system open enough for the public to know how scary some detainees really are and adversarial enough to credibly separate the wheat from the chaff.

If it fails again to create such a system, the result of Thursday's decision will not be a resolution of the dispute over Guantanamo. It will be endless litigation over the hard questions all of these court battles have managed so assiduously to avoid: Whom does America want to detain outside its criminal justice apparatus? What procedures does it want to employ for evaluating a given captive? And what rights should that captive have?

The court has narrowed Congress' latitude to answer these questions, but it thankfully has not relieved the political system of its burden. Congress cannot afford to shirk that burden any longer.

Benjamin Wittes, a former Washington Post editorial writer, is a fellow and research director in public law at the Brookings Institution. He wrote this commentary for The Washington Post.