Pacem in Terris §68

⁶⁸ In determining what form a particular government shall take, and the way in which it shall function, a major consideration will be the prevailing circumstances and the condition of the people; and these are things which vary in different places and at different times. We think, however, that it is in keeping with human nature for the State to be given a form which embodies a threefold division of public office properly corresponding to the three main functions of public authority. In such a State a precise legal framework is provided, not only for the official functions of government, but also for the mutual relations between citizens and public officials. This will obviously afford sure protection to citizens, both in the safeguarding of their rights and in the fulfilment of their duties.