The four traditional functions of criminal punishment are Retribution (an eye for an eye, or the punishment meeting the crime) Deterrence (for fear of punishmen

The four traditional functions of criminal punishment are Retribution (an eye for an eye, or the punishment meeting the crime) Deterrence (for fear of punishment, people do not commit crimes), Rehabilitation (correcting the behavior), and Incapacitation (someone in jail cannot commit crimes). One downside to retribution only is that the odds of being caught for a crime are less than 100%, so someone stands to gain more than they stand to lose by breaking the crime. For example if the punishment for tax perjury was commensurate with my ill gotten gains, I wouldn't have any reason outside of a personal moral framework not to lie. But if instead I can go to prison for 3 years, a good chance to save a fair chunk of money is much less attractive.