An Eye for an eye, a tooth for a tooth, and a life for a life, is a common theoretical view of punishment and the deterrence of crime. Why would anyone commit an act of violence against another if they knew they would have the same act committed to them? A proponent of the death penalty would argue exactly this point. Capital punishment has been a successful deterrent since early biblical times. People were stoned to death for a variety of reasons, anything from infidelity to heresy to treason. During these times, capital punishment was successfully used as a deterrent because the chances of the punishment being carried out were absolute. If the crime were committed, the punishment would be given. The effectiveness of capital punishment in deterring crime relies on precisely this point, say proponents. If the punishment for murder were certain death, there would be fewer people willing to take their chances, because the ramifications would be clear and decisive. .
During the mid-1970s Isaac Ehrlich found a strong correlation between the number of executions and the murder rate, saying that each execution prevented seven or eight murders in effect (Henderson 259). Since his publication, no other researcher has been able to find similar results, thus striking a resounding blow to Ehrlich's credibility. Another man, author Jay Johansen, finds a direct connection between the number of murders per million people and the number of executions in that year. In his essay and graphs, Johansen points out that the homicide rate drops steadily during the years when executions are on the rise and rates rise sharply when executions are brought to a halt or held to very low number. His point is most obvious between 1970 and 1976 when capital punishment was abolished. .
Another variable that proponents say effects the capability of the death penalty, as a deterrent is the speediness in which the punishment is carried out.
