Deterrence is the use of punishment as a threat to deter people from offending. Deterrence is often contrasted with retributivism, which holds that punishment is a necessary consequence of a crime and should be calculated based on the gravity of the wrong done.
The concept of deterrence has two key assumptions: the first is that specific punishments imposed on offenders will "deter" or prevent them from committing further crimes; the second is that fear of punishment will prevent others from committing similar crimes. The notion of deterrence underlines the criminal justice systems in most democratic societies, although punishment and incarceration traditionally have a variety of goals – including incapacitation, punishment, deterrence and rehabilitation. In the United States in particular (but also in other Western democracies), sentencing policy initiatives have often been enacted with the goal of enhancing the deterrent effect. Under the rubric of "getting tough on crime", policies such as "mandatory minimums", "truth in sentencing", and "three strikes and you’re out" have been designed to deter offending with the threat of substantial terms of imprisonment.
Deterrence can be divided into three separate categories.
Specific deterrence focuses on the individual in question. The aim of these punishments is to discourage the criminal from future criminal acts by instilling an understanding of the consequences.
General or indirect deterrence focuses on general prevention of crime by making examples of specific deviants. The individual actor is not the focus of the attempt at behavioral change, but rather receives punishment in public view in order to deter other individuals from deviance in the future. The argument that deterrence, rather than retribution, is the main justification for punishment is a hallmark of the rational choice theory and can be traced to Cesare Beccaria whose well-known treatise On Crimes and Punishments (1764) condemned torture and the death penalty, and Jeremy Bentham who made two distinct attempts during his life to critique the death penalty.
Incapacitation is considered by some to be a subset of specific deterrence. Incapacitation aims to prevent future crimes not by rehabilitating the individual but rather from taking away his ability to commit such acts. Under this theory, criminals are put in jail not so that they will learn the consequence of their actions but rather so that while there they will be unable to engage in crime.
Not all crime deterrence comes from a criminal justice system. Controversial academic Gary Kleck concludes evidence suggests that private gun ownership and use significantly deter crime, although several academics have since concluded otherwise.
Marginal deterrence 
Marginal deterrence is a principle in theory of criminal justice, stating that a more severe crime should be punished harder than a lesser crime, and that a series of crimes should be punished harder than a single crime of the same kind.
Marginal deterrence is intended to deter criminals to limit their criminal acts. Without marginal deterrence, a criminal could benefit from committing additional crimes, or using illegal methods to suppress law enforcement, witnesses or evidence. As an example, if robbery without force gave the same punishment as robbery by murder, a robber could make a rational choice to kill the victims, to evade their testimonies.
Research has shown that increasing the severity of a punishment does not have much effect on crime, while increasing the certainty of punishment does have a deterrent effect. "Clearly, enhancing the severity of punishment will have little impact on people who do not believe they will be apprehended for their actions.".
The use of 'heavy' punishment has been described as "the least effective and least fair principle of sentencing". A study by a Canadian criminologist Paul Gendreau brought together the results of 50 different studies of the deterrent effect of imprisonment involving over 300,000 offenders. The report said: "None of the analyses found imprisonment reduced recidivism. The recidivism rate for offenders who were imprisoned as opposed to given a community sanction was similar. In addition, longer sentences were not associated with reduced recidivism. In fact the opposite was found. Longer sentences were associated with a 3% increase in recidivism. This finding suggests some support for the theory that prison may serve as a ‘school for crime’ for some offenders".
A 2000 study by Uri Gneezy and Aldo Rustichini, A Fine Is a Price, has shown that introducing a fine for a previously unfined behavior may increase, rather than decrease, the unwanted behavior. This happens as the fine replaces a previous set of moral or ethical norms, and if it is low enough, it is going to be easier to overcome than the non-monetary criticism was. In other words, putting a price on something previously not on a market changes its perception drastically, and on occasion it can change it contradictory to what a deterrence theory would predict.
See also 
- Summerfield, Morgan (May 18, 2006). "Evolution of Deterrence Crime Theory". Retrieved 13 October 2012.
- Wright, Valerie (November 2010). "Deterrence in Criminal Justice: Evaluating Certainty vs. Severity of Punishment". The Sentencing Project. Retrieved 13 October 2012.
- Bedau, Hugo Adam (1983). "Bentham's utilitarian critique of the death penalty". The Journal of Criminal Law and Criminology (Northwestern University School of Law) 74 (3): pp. 1033–1065. JSTOR 1143143.
- Kleck, Gary (February 1988). "Crime control through the private use of armed force". Social Problems 35 (1): 1–21.
- Philip J. Cook; Jens Ludwig; David Hemenway, “The gun debate’s new mythical number: How many defensive uses per year?”, Journal of Policy Analysis and Management, 16.3, 1997
- David Hemenway, “The myth of millions of annual self-defense gun use: A case study of survey overestimates of rare events”, Chance – American Statistical Association, 10.3, 1997
- Philip J. Cook; Jens Ludwig, “Defensive Gun Uses: New Evidence from a National Survey” Journal of Quantitative Criminology, 14.2, 1998
- David Hemenway; Deborah Azrael, “The Relative Frequency of Offensive and Defensive Gun Uses: Results from a National Survey”, Violence and Victims, 15.3, 2000
- Daniel Webster; Jens Ludwig, “Myths about Defensive Gun Use and Permissive Gun Carry Laws”, Berkeley Media Studies Group, 2000
- David Hemenway; Mary Vriniotis, “Comparing the Incidence of Self-Defense Gun Use and Criminal Gun Use”, Harvard Injury Control Research Center, 2009
- A Note on Marginal Deterrence, by Steven Shavell
- Martin, Jacqueline (2005). The English Legal System (4th ed.), p. 176. London: Hodder Arnold. ISBN 0-340-89991-3.
- Gendreau, P, Goggin, C, Cullen FT, The effects of prison sentences on recidivism, User Report: Office of the Solicitor General, Canada, 1999, p24.
- Shirky, Clay (2010). Cognitive Surplus: Creativity and Generosity in a Connected Age. Penguin. pp. 131–134. ISBN 978-1-59420-253-7. Retrieved 11 October 2012.