By 'justice', I understand nothing more than that bond which is necessary to keep the interest of individuals united, without which men would return to their original state of barbarity. All punishments which exceed the necessity of preserving this bond are, in their nature, unjust.
In order that punishment should not be an act of violence perpetrated by one or many upon a private citizen, it is essential that it should be public, speedy, necessary, the minimum possible in the given circumstances, proportionate to the crime, and determined by the law.
If someone were to say that life at hard labor is as painful as death and therefore equally cruel, I should reply that, taking all the unhappy moments of perpetual slavery together, it is perhaps even more painful, but these moments are spread out over a lifetime, and capital punishment exercises all its power in an instant.
It is the task of theologians to establish the limits of justice and injustice regarding the intrinsic goodness or wickedness of an act; it is the task of the observer of public life to establish the relationships of political justice and injustice, that is, of what is useful or harmful to society.
Men's most superficial feelings lead them to prefer cruel laws. Nevertheless, when they are subjected to them themselves, it is in each man's interest that they be moderate, because the fear of being injured is greater than the desire to injure.
Laws are the terms by which independent and isolated men united to form a society, once they tired of living in a perpetual state of war where the enjoyment of liberty was rendered useless by the uncertainty of its preservation. They sacrificed a portion of this liberty so that they could enjoy the remainder in security and peace.