Communitas perfecta ("perfect community") or societas perfecta ("perfect society") is the Latin name given to one of several ecclesiological, canonical, and political theories of the Catholic Church. The doctrine teaches that the church is a self-sufficient or independent group which already has all the necessary resources and conditions to achieve its overall goal (final end) of the universal salvation of mankind. It has historically been used in order to define church-state relations and to provide a theoretical basis for the legislative powers of the church in the philosophy of Catholic canon law.
Its origins can be traced to the Politics of Aristotle, who described the Polis as a whole made of several imperfect parts, i.e. the consummation of natural communities such as the family and the village. The "perfect community" was originally developed as a theory of political society. The most sovereign political organization (the Polis) can attain the end of the community as a whole (happiness) better than any of the subordinate parts of the community (family, village, etc.). Since it can attain its end (telos) by its own powers and the resources within itself, then it is self-sufficient. It is self-sufficiency that is the defining element of the polis.
The idea of "perfect community" was also present in medieval philosophy. In direct reference to Aristotle, Thomas Aquinas mentions the state (civitas) as a perfect community (communitas perfecta):
As one man is a part of the household, so a household is a part of the state: and the state is a perfect community, according to Polit. i, 1. And therefore, as the good of one man is not the last end, but is ordained to the common good; so too the good of one household is ordained to the good of a single state, which is a perfect community. Consequently he that governs a family, can indeed make certain commands or ordinances, but not such as to have properly the force of law.
Aquinas never referred to the church as a perfect community in his writings. If Aquinas and medieval writers had any notion of communitas perfecta being applied to the church, it was not clearly expressed and was not a clear basis for the societas perfecta theory used in later controversies between church and state.
During Enlightenment period, the Societas Perfecta doctrine was strongly affirmed in order to better protect the church from secular encroachments. It was also mentioned in the magisterium of the Thomistic revivalist pontiffs such as Pius IX. And especially Leo XIII, in his encyclical Immortale Dei, explains this teaching in relation to the church:
It is a perfect society of its own kind and their own right, since it everything for their existence and their effectiveness is necessary, in accordance with the will and power of the grace of their Founder in and of itself owns. As the goal of the Church is more sublime, its power is always far superior, and it can therefore not be considered less than the Civil state, as to not be in a state of subordination.
The two perfect societies correspond to two forces, the church and state:
The one responsible for the care of the divine dimension, the other for the human. Each one is in the highest of its kind: each has certain limits within which it moves, borders that emerged from the nature and purpose of each of the next two forces showed.
Until the Second Vatican Council, the doctrine of the two perfect societies of Leo XIII was held to be official in theological studies. During the council itself, as well as in the new 1983 Code of Canon Law itself, the doctrine was no longer explicitly mentioned and the Aristotelian "Perfect Community" was all but replaced by the biblical "People of God". In the modern Catholic post-conciliar theology, its discussion is limited to theologians and academics. Its near-abandonment in discourse has proven controversial.
It cannot be disputed that the duties of Church and State belong to different orders. Church and state are in their own area perfect societies. That means: They have their own legal system and all necessary resources. They are also, within their respective jurisdiction, entitled to apply its laws. On the other hand, it must not be overlooked that they are both aiming at a similar welfare, namely that the people of God is to obtain eternal salvation.
This theology was largely overshadowed by the biblical theology of the church as the mystici corporis Christi (mystical body of Christ), which began to be more fully developed in the early 20th century and was affirmed by Pope Pius XII in 1943.