Book 2, Chapter 12: The Division of the Laws explained simply

CHAPTER XII THE DIVISION OF THE LAWS If the whole is to be set in order, and the commonwealth put into the best possible shape, there are various relations to be considered. First, there is the action of the complete body upon itself, the relation of the whole to the whole, of the Sovereign to the State; and this relation, as we shall see, is made up of the relations of the intermediate terms. The laws which regulate this relation bear the name of political laws, and are also called fundamental laws, not without reason if they are wise. For, if there is, in each State, only one good system, the people that is in possession of it should hold fast to this; but if the established order is bad, why should laws that prevent men from being good be regarded as fundamental? Besides, in any case, a people is always in a position to change its laws, however good; for, if it choose to do itself harm, who can have a right to stop it? The second relation is that of the members one to another, or to the body as a whole; and this relation should be in the first respect as unimportant, and in the second as important, as possible. Each citizen would then be perfectly independent of all the rest, and at the same time very dependent on the city; which is brought about always by the same means, as the strength of the State can alone secure the liberty of its members. From this second relation arise civil laws. We may consider also a third kind of relation between the individual and the law, a relation of disobedience to its penalty. This gives rise to the setting up of criminal laws, which, at bottom, are less a particular class of law than the sanction behind all the rest. Along with these three kinds of law goes a fourth, most important of all, which is not graven on tablets of marble or brass, but on the hearts of the citizens. This forms the real constitution of the State, takes on every day new powers, when other laws decay or die out, restores them or takes their place, keeps a people in the ways in which it was meant to go, and insensibly replaces authority by the force of habit. I am speaking of morality, of custom, above all of public opinion; a power unknown to political thinkers, on which none the less success in everything else depends. With this the great legislator concerns himself in secret, though he seems to confine himself to particular regulations; for these are only the arc of the arch, while manners and morals, slower to arise, form in the end its immovable keystone. Among the different classes of laws, the political, which determine the form of the government, are alone relevant to my subject.