The doctrine of Communitas Perfecta ("Perfect Community") or Societas Perfecta ("Perfect Society") teaches that the Church is a self-sufficient or independent society 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 best define Church-State relations. Its origins are in Aristotelian political philosophy, although its adaptation to ecclesiology was done by the Scholastics. The doctrine was widely used in Neoscholastic circles before the Second Vatican Council. After the Council, the doctrine all but vanished from ecclesiological discourse.
Mystical Body of Christ
People of God
Subsistence is the doctrine that the Church of Christ "subsists in" the Catholic Church. The doctrine is in continuity with the previous phrasing of Mystici corporis Christi that the Church of Christ "is" (est) the Catholic Church, although some theologians have interpreted the phrase to be a rupture with the previous tradition.
Subsistit in is a term taken from Lumen Gentium paragraph 8:
This Church constituted and organized in the world as a society, subsists in the Catholic Church, which is governed by the successor of Peter and by the Bishops in communion with him, although many elements of sanctification and of truth are found outside of its visible structure.
The proper interpretation of subsistence has been controversial since the Second Vatican Council introduced the phrase; the Congregation for the Doctrine of the Faith has issued various interpretations confirmed by the pope, while some dissident theologians put forth more radical interpretations.