It is not only the common interest of mankind that crimes should not be committed, but that crimes of every kind should be less frequent, in proportion to the evil they produce to society Therefore, the means made use of by the legislature to prevent crimes, should be more powerful, in proportion as they are destructive of the public safety and happiness, and as the inducements to commit them are stronger. Therefore there ought to be a fixed proportion between crimes and punishments.

It is impossible to prevent entirely all the disorders which the passions of mankind cause in society. These disorders increase in proportion to the number of people, and the opposition of private interests. If we consult history, we shall find them increasing, in every state, with the extent of dominion. In political arithmetic, it is necessary to substitute a calculation of probabilities to mathematical exactness. That force which continually impels us to our own private interest, like gravity, acts incessantly, unless it meets with an obstacle to oppose it. The effects of this force are the confused series of human actions. Punishments, which I would call political obstacles, prevent the fatal effects of private interest, without destroying the impelling cause, which is that sensibility inseparable from man. The legislator acts, in this case, like a skilful architect, who endeavours to counteract the force of gravity by combining the circumstances which may contribute to the strength of his edifice.

The necessity of uniting in society being granted, together with the conventions, which the opposite interests of individuals must necessarily require, a scale of crimes may be formed, of which the first degree should consist of those which immediately tend to the dissolution of society, and the last, of the smallest possible injustice done to a private member of that society. Between these extremes will be comprehended, all actions contrary to the public good, which are called criminal, and which descend by insensible degrees, decreasing from the highest to the lowest. If mathematical calculation could be applied to the obscure and infinite combinations of human actions, there might be a corresponding scale of punishments, descending from the greatest to the least; but it will be sufficient that the wise legislator mark the principal divisions, without disturbing the order, lest to crimes of the first degree, be assigned punishments of the last. If there were an exact and universal scale of crimes and punishments, we should then have a common measure of the degree of liberty and slavery, humanity and cruelty, of different nations.

Any action, which is not comprehended in the above mentioned scale, will not be called a crime, or punished as such, except by those who have an interest in the denomination. The uncertainty of the extreme points of this scale, hath produced a system of morality which contradicts the laws; a multitude of laws that contradict each other; and many which expose the best men to the severest punishments, rendering the ideas of vice and virtue vague and fluctuating, and even their existence doubtful. Hence that fatal lethargy of political bodies, which terminates in their destruction.

Whoever reads, with a philosophic eye, the history of nations, and their laws, will generally find, that the ideas of virtue and vice, of a good or a bad citizen, change with the revolution of ages; not in proportion to the alteration of circumstances, and consequently conformable to the common good; but in proportion to the passions and errors by which the different lawgivers were successively influenced. He will frequently observe, that the passions and vices of one age, are the foundation of the morality of the following; that violent passion, the offspring of fanaticism and enthusiasm, being weakened by time, which reduces all the phenomena of the natural and moral world to an equality, become, by degrees, the prudence of the age, and an useful instrument in the hands of the powerful or artful politician. Hence the uncertainty of our notions of honour and virtue; an uncertainty which will ever remain, because they change with the revolutions of time, and names survive the things they originally signified; they change with the boundaries of states, which are often the same both in physical and moral geography.

Pleasure and pain are the only springs of action in beings endowed with sensibility. Even among the motives which incite men to acts of religion, the invisible Legislator has ordained rewards and punishments. From a partial distribution of these will arise that contradiction, so little observed, because so common; I mean, that of punishing by the laws the crimes which the laws have occasioned. If an equal punishment be ordained for two crimes that injure society in different degrees, there is nothing to deter men from committing the greater, as often as it is attended with greater advantage.