Satis cognitum
Satis cognitum is an encyclical of Pope Leo XIII dated 29 June 1896 on the unity of the Church, and some heresies of his time. Content "The pontificate of Leo marked a change in how popes exercised their teaching authority. With Leo, the popes begin to offer theological treatments on important topics. It also saw a beginning the Church's participation in ecumenism. The encyclical is an invitation to those who are without the Church to return to it. It is an affirmation of the Church's unity, and the role of the Magisterium in preserving that unity,<ref>{{cite book | url = https://books.google.com/books?id=GAlVCQAAQBAJ&pg=PA245 | last= Sakowski | first = Derek | title =The ecclesiological Reality of Reception: Considered as a solution to the debate over the ontological priority of the universal church | publisher = Gregorian Biblical Book Shop | date= 2014 | page = 245 | isbn= 9788878392717}}</ref> through the threefold responsibilities of sanctifying, governing and teaching. The document contains an extensive articulation of and apologia for Catholic ecclesiology as it relates to the Church's unity, one of the four marks of the Church according to the Niceno-Constantinopolitan Creed, which professes belief in "one, holy, catholic, and apostolic Church." The purpose