A constitution is the arrangement of magistracies in a state, especially of the highest of all. The government is everywhere sovereign in the state, and the constitution is in fact the government. For example, in democracies the people are supreme, but in oligarchies, the few; therefore we say that these two forms of government are different, and so in other cases.
First, let us consider what is the purpose of a state and how many forms of government there are by which human society is regulated. When drawing a distinction between household management and the rule of a master, man is by nature a political animal. And therefore, men, even when they do not require one another’s help, desire to live together all the same and are in fact brought together by their common interests in proportion as they severally attain to any measure of well-being. This is certainly the chief end, both of individuals and of states. And also for the sake of mere life (in which there is possibly some noble element), mankind meets together and maintains the political community, so long as the evils of existence do not greatly overbalance the good. And we all see that men cling to life even in the midst of misfortune, seeming to find in it a natural sweetness and happiness.
There is no difficulty in distinguishing the various kinds of authority; they have been often defined already in popular works. The rule of a master, although the slave by nature and the master by nature have in reality the same interests, is nevertheless exercised primarily with a view to the interest of the master, but accidentally considers the slave, since, if the slave perishes, the rule of the master perishes with him. However, the government of a wife and children and of a household, which we have called household management, is exercised in the first instance for the good of the governed or for the common good of both parties, but essentially for the good of the governed, as we see to be the case in medicine, gymnastics, and the arts in general, which are only accidentally concerned with the good of the artists themselves. (For there is no reason why the trainer may not sometimes practice gymnastics, and the pilot is always one of the crew.) The trainer or the pilot considers the good of those committed to his care. But when he is one of the persons taken care of, he accidentally participates in the advantage, for the pilot is also a sailor, and the trainer becomes one of those in training. And so in politics: when the state is framed upon the principle of equality and likeness, the citizens think that they ought to hold office by turns. In the order of nature everyone would take his turn of service; and then again, somebody else would look after his interest, just as he, while in office, had looked after theirs. (That was originally the way.) But nowadays, for the sake of the advantage that is to be gained from the public revenues and from office, men want to be always in office. One might imagine that the rulers, being sickly, were only kept in health while they continued in office; in that case we may be sure that they would be hunting after places. The conclusion is evident: governments, which have a regard for the common interest, are constituted in accordance with strict principles of justice and are therefore true forms, but those that regard only the interest of the rulers are all defective and perverted forms, for they are despotic, whereas a state is a community of freemen.