The Eighth Amendment to the United States Constitution prohibits the infliction of "cruel and unusual punishments." Virtually every state constitution also has its own prohibition against such penalties.
In a nutshell, the cruel and unusual punishment clause measures a particular punishment against society's prohibition against inhuman treatment. It prevents the government from imposing a penalty that is either barbaric or far too severe for the crime committed.
The English Declaration of Rights of 1689 is the source of the prohibition against cruel and unusual punishment. When the Declaration was issued, however, fairly gruesome punishment was meted out as a matter of course. For example, dozens of offenses, including those as minor as grand theft, were punishable by death. America's adoption of the ban on cruel and unusual punishment took place within a similar context—the men who wrote the Constitution were aware of harsh colonial practices such as repeatedly plunging low-level offenders under water.
While the English framers' purpose was to outlaw savage and torturous forms of punishment, modern readers may wonder how the punishments of the day escaped censure under the lofty ban. In America, many punishments survived under the cruel and unusual punishment clause simply because they had long been permissible. Courts upheld punishments such as disenfranchisement for dueling, whipping for illegal gambling, and banishment for larceny because these were acceptable English (and hence American) practices.
However, American courts considered certain historical punishments inherently cruel and unusual. For centuries, governments throughout the world had inflicted punishments like crucifixion, burning at the stake, breaking on the wheel, quartering, and the rack and thumbscrew. While the United States practiced certain lesser forms of physical punishment even after the Eighth Amendment, these practices eventually abated. Nevertheless, prisoners today continue to argue, sometimes successfully, that particular conditions cross the line.
The practical meaning of "cruel and unusual" has troubled courts for generations, because it is difficult to imagine that any punishment, no matter how barbarous, should be accepted simply because it is "usual." As long ago as 1910 the Supreme Court acknowledged that "what constitutes a cruel and unusual punishment has not been exactly decided." (Weems v. United States, 217 U.S. 349 (1910).) Today, courts have nearly read the term "unusual" out of the Amendment. Some have even suggested that the word was inadvertently included in the English Bill of Rights in the first place. (See, for example, Furman v. Georgia, 408 U.S. 238, 331 (1972) (Marshall, J., concurring).)
Hoping to give the cruel and unusual punishment clause a more workable application, the Supreme Court began to follow the "evolving standards of decency" test. In 1958 Chief Justice Earl Warren wrote that the clause "must draw its meaning from the evolving standards of decency that mark the progress of a maturing society." (Trop v. Dulles, 356 U.S. 86, 100-101 (1958).) The Court continues to follow the evolving standards approach today.
"Originalists" advocate an alternative method of determining whether a punishment is cruel and unusual. Under this view, unconstitutional punishments are limited to those that were historically unacceptable because of their inherent brutality. (John F. Stinneford, The Original Meaning of "Unusual": The Eighth Amendment as a Bar to Cruel Innovation, 102 Nw.U. L. Rev. 1739 (2008).) Interpreted strictly, this minority approach would allow for any punishment that was still in practice by 1790. (Id.)
To the originalists' dismay, public opinion is crucial in evaluating whether a punishment is cruel and unusual under the evolving standards test. The Supreme Court gauges this opinion in part by looking to the states' legislatures and juries. For example, the Court held that the death penalty is an unconstitutional punishment for the crime of rape. (Coker v. Georgia, 433 U.S. 584 (1977).) It rested its opinion in large part on the fact that only one of the 50 states authorized this sentence. It also focused on the reluctance of juries in that state to impose the death sentence for rape convictions. Similarly, the Court relied heavily on a trend toward abolition of the death penalty for the intellectually disabled and for minors . (Atkins v. Virginia, 536 U.S. 304 (2002); Roper v. Simmons, 543 U.S. 551 (2005).)
Importantly though, the Court has noted that it will not ignore its own judgment as to whether a punishment is reasonable. (Atkins, 536 U.S. at 122.)
The evolving standards approach looks not only at the nature of the punishment in each case, but also whether it fits the severity of the crime. Courts look to the sentences for other criminals in the state where the crime occurred, and the sentences for the same crime in other states. When more serious offenses result in less punishment than the punishment being examined, or when other states punish the identical crime less severely, a court is likely to conclude that the punishment does not fit the crime. However, a punishment is not unconstitutional simply because it is severe. The Eighth Amendment forbids only grossly excessive penalties.
When a court concludes that a particular sentence is disproportionate to the offense committed, it will strike the sentence. An example is a 36-year sentence for passing a series of bad checks. (Faulkner v. State, 445 P.2d 815 (Alaska 1968).) But the U.S. Supreme Court once famously held that a 25-year-to-life sentence for stealing three golf clubs under a state's "three strikes" law wasn't unconstitutional. (Ewing v. California, 538 U.S. 11 (2003).) Indeed, under the Eighth Amendment, no particular term of years in prison is forbidden, nor is the death penalty inherently cruel or unusual.
The cruel and unusual punishment clause also applies to conditions of incarceration. Prison officials may not deprive inmates of "the basic necessities of life, which include reasonably adequate food, clothing, shelter, sanitation, and necessary medical attention." (Newman v. State of Alabama, 559 F.2d 283 (5th Cir. 1977).) Nor may they "maliciously and sadistically" use force to harm inmates. (Hudson v. McMillian, 503 U.S. 1 (1992).)