From The Art and Popular Culture Encyclopedia
In ethics and law, "Let the punishment fit the crime" is the principle that the severity of penalty for a misdeed or wrongdoing should be reasonable and proportional to the severity of the infraction. The concept is common to most cultures throughout the world. Its presence in the ancient Jewish culture is shown by its inclusion in the law of Moses, specifically in Deuteronomy 19:17-21, which includes the punishments of "life for life, eye for eye, tooth for tooth, hand for hand, foot for foot." Many other documents reflect this value in the world's cultures. However, the judgment of whether a punishment is appropriately severe can vary greatly between cultures and individuals.
Proportionality requires that the level of punishment be scaled relative to the severity of the offending behaviour. However, this does not mean that the punishment has to be equivalent to the crime. A retributive system must punish severe crime more harshly than minor crime, but retributivists differ about how harsh or soft the system should be overall.