Cesare Beccaria theorized on free will, rational manner and manipulability; he believed that free will enables people to make their own choices, and that people have a rational manner that they apply toward decisions with the ultimate goal of achieving personal satisfaction. His treatise, "On Crimes and Punishments," and his theories in general are still discussed in modern times.
According to Beccaria, the law exists to benefit society and to preserve social contract, but because the interests of people sometimes conflict with society, crime results, usually out of self interests of the criminal. Beccaria believed that people could be dissuaded from crime if the punishment that results is greater than the benefits of the crime. This makes crime an illogical choice.
In its time, Beccaria's treatise identified the need for reformation in the criminal justice system, which he felt was antiquated and barbaric. Beccaria believed in rights for criminals and their victims, and much of his theories involved crime prevention and appropriate punishments for crimes.
Notably, "On Crimes and Punishments" served as a guide for the founding fathers when they were drafting the United States Constitution and the Bill of Rights. Today, his theories have been applied to arguments regarding the abolishment of the death penalty, swift punishment and truth in sentencing.