Sentencing theory

Sentencing theory is the philosophy governing the determination of what response should be taken against an aggressor of justly held life, liberty or property after he has been apprehended and it has been proven that he committed the crime. Sentencing theories include retribution (punishment), restitution, deterrence, and rehabilitation. In practice (and in theory) law has a tendency to implement a mixture of several or all of the theories. According to Murray Rothbard, "The libertarian believes that a criminal loses his rights to the extent that he has aggressed upon the rights of another, and therefore that it is permissible to incarcerate the convicted criminal and subject him to involuntary servitude to that degree." Ludwig von Mises writes: Liberalism neither wishes to nor can deny that the coercive power of the state and the lawful punishment of criminals are institutions that society could never, under any circumstances, do without. However, the liberal believes that the purpose of punishment is solely to rule out, as far as possible, behavior dangerous to society. Punishment should not be vindictive or retaliatory. The criminal has incurred the penalties of the law, but not the hate and sadism of the judge, the policeman, and the ever lynch-thirsty mob.

Public good
Deterrence and incapacitation are sometimes described as public goods since they are indivisible and nonexcludable. John Hasnas argues that like lighthouses, television, and internet, crime prevention can be supplied non-politically.

Optimal crime rate
Economic calculation problems arise in sentencing, as with other government services. The "parsimony provision" of provides, for instance, that "The court shall impose a sentence sufficient, but not greater than necessary, to comply with the purposes" of sentencing. The parsimony provision does not specify how much deterrence, protection of the public, and rehabilitation courts should strive to impose a sentence that is sufficient to provide. No cost-benefit analysis is prescribed. Laurent Carnis notes that the classical school of crime "searches for the optimal number of crimes for society (Becker 1968; Ehrlich, 1996). This optimal number is reached when the government authorities have minimized the social cost: the marginal cost equals the marginal revenue. It is supposed that the marginal cost for society of suffering the crime is the same as the cost to avoid it. For this optimal level of crime, the authorities, on behalf of society, define a level of tolerance. Society must tolerate this amount of crime to avoid waste."

Neoclassical theory holds that losses from crime will be perceived differently among social and economic groups within any society. Therefore, it is up to the political process to determine how the interests of various groups will be reconciled or which groups will be able to impose their will on the rest of society. Libertarian theory holds that in a free market, people would voluntarily decide what resources should be allocated to crime prevention, and that the resulting allocation would more closely approximate what is optimal for maximizing utility.

Practices of governmental judicial systems
In governmental judicial systems, it is deemed important for the courts to at least pay lip service to the parsimony provision. In Ministro-Tapia, No. 05-5101 (2d Cir. Nov. 28, 2006), the appellate court stated that "if a district court were explicitly to conclude that two sentences equally served the statutory purpose of § 3553, it could not, consistent with the parsimony clause, impose the higher." In U.S. v. Rosa, the district court was reversed after it stated that the sentence it was imposing was harsher than necessary. The upshot of this is that courts will have to be careful not to explicitly make such statements.