"God! what darkness here!" cries Florestan in Beethoven's Fidelio, speaking alone to the audience from the underground cell in which he has been imprisoned. Beethoven's youthful Jacobinism has not aged well, but many of the causes that animated his politics are as worthy now as they were in his own era. This is true not least of his evident horror of solitary confinement, which he shared with Dumas, Dickens, and many other 19th-century worthies. It is the moral seriousness of the uncompromising revolutionary that makes the famous "Prisoners' Chorus" among the most stirring moments in the history of Western art music:

Oh what joy, in the open air
Freely to breathe again!
Up here alone is life!
The dungeon is a grave. [Fidelio]

I was recently surprised to find myself thinking that Justice Sonia Sotomayor has done something worthy, politically if not aesthetically, of the great composer. Sotomayor deserves a nation's gratitude for her statement issued Tuesday following the Supreme Court's refusal to hear the case of prisoners — one now dead — who had been held in solitary confinement at the Colorado State Penitentiary. "A punishment need not leave scars to be cruel and unusual," Sotomayor wrote. "To deprive a prisoner of any outdoor exercise for an extended period of time in the absence of an especially strong basis for doing so is deeply troubling — and has been recognized as such for many years." According to filings, the men were allowed to leave their cells for only one hour five days a week in order to visit an "exercise area," apparently in keeping with state regulations concerning prisoners' right to be outdoors. This is what the state believed compliance looked like:

[The exercise room] has two vertical "windows," approximately five feet by six inches in size, which are not glassed but instead are covered with metal grates. The grates have holes approximately the size of a quarter that open to the outside. The inmate can see through the holes, can sometimes feel a breeze, and can sometimes feel the warmth of the sun. This is his only exposure of any kind to fresh air. [Anderson v. Colorado]

One of the petitioners in the case spent 11 years living in such conditions. He died in May, three years after his release. "While we do not know what caused his death," Sotomayor wrote, "we do know that solitary confinement imprints on those that it clutches a wide range of psychological scars."

The petitioners were not alone. As many as 100,000 American prisoners now live in indefinite solitary confinement. While it is heartening that this figure is much lower than the total even half a decade ago, long-term solitary confinement is actually becoming more common in a handful of states. In Louisiana, where nearly one fifth of the prison population lives in isolation, Albert Woodfox spent 43 years in a six by nine foot cell deprived of any contact with other human beings. Woodfox also died not long after his release from prison.

The continued practice of indefinite solitary confinement is a failure of administration, whether the Supreme Court chooses to correct it or not. I say "failure" because it does not succeed in its stated aims. Solitary confinement fails to make prisoners less violent. It exacerbates mental illness in some prisoners and is the cause of it for many others; a recent study revealed that at present some 4,000 inmates suffering from mental illness are being held in solitary confinement in American prisons. In New Mexico, 64 percent of inmates who are mentally ill are in "the shoe."

Solitary confinement is also something far more serious than an administrative failure. Putting men away in cells for weeks, months, and years at a time is a failure of the moral imagination, and a typically modern one. Unable to conceive of a fate worse than death for the very wicked, we have convinced ourselves that it is more merciful to torture a man for decades than to execute him swiftly.

Our wisest ancestors knew better. I have very few kind words for the legacy of the recently retired Justice Anthony Kennedy, but his concurrence in Davis v. Ayala, a death penalty case, was one of the most memorable things written recently by an American judge. "It is likely [that the respondent] has been held for all or most of the past 20 years or more in a windowless cell no larger than a typical parking spot for 23 hours a day; and in the one hour when he leaves it, he likely is allowed little or no opportunity for conversation or interaction with anyone," Kennedy wrote. "Too often, discussion in the legal academy and among practitioners and policymakers concentrates simply on the adjudication of guilt or innocence. Too easily ignored is the question of what comes next. Prisoners are shut away — out of sight, out of mind." Even poor Dr. Manette in A Tale of Two Cities, he added, "had a work bench and tools to make shoes, a type of diversion no doubt denied many of today's inmates."

In her statement on Tuesday, Sotomayor revived the proud tradition of bringing the greatest novelist in our language to bear upon judicial questions, observing that Dickens' portrayal of Manette was inspired by his first-hand knowledge of solitary confinement in a Philadelphia prison, a subject he treated in American Notes:

[The prisoner] is led to the cell from which he never again comes forth, until his whole term of imprisonment has expired. He never hears of wife and children; home or friends; the life or death of any single creature. He sees the prison-officers, but with that exception he never looks upon a human countenance, or hears a human voice. He is a man buried alive; to be dug out in the slow round of years; and in the mean time dead to everything but torturing anxieties and horrible despair. [American Notes]

I am not suggesting that inmates ought never to be separated for a time from the rest of the prison population — a 12-hour cool-down period after a fight or some other serious disciplinary infraction is perfectly reasonable. And there are certainly some prisoners — homicidal maniacs, serial rapists, cannibals, torturers — whose liberty would pose a danger to both staff and other inmates, though in such cases the death penalty seems more fitting and far less cruel.

But men like Jonathan Apodaca and Joshua Virgil are not Hannibal Lecters. They have argued that there was no compelling reason of security for their solitary detention, only the caprice of their jailers. If this is true — thanks to the Supreme Court's official incuriosity we may never know — it is a monstrous crime. To have denied them sunlight and open air and the company of their fellow men was as barbarous as denying them food or water or medicine. It was a denial of their humanity. No earthly judge has the right to issue a spiritual, as opposed to a physical, sentence of death.

Solitary confinement is torture. It no more deserves a place in a civilized society than the thumbscrew or the rack.