Filioque (Ecclesiastical Latin: [filiˈɔkwe]), Latin for "and (from) the Son", is a phrase found in the form of Nicene Creed in use in most of the Western Christian churches. It is not present in the Greek text of the Nicene Creed as originally formulated at the First Council of Constantinople, which says only that the Holy Spirit proceeds "from the Father":
Together with papal primacy, differences over this doctrine have been and remain the primary causes of schism between the Western and Eastern Orthodox churches. The Filioque has been an ongoing source of conflict between the East and West, contributing, in part, to the East-West Schism of 1054 and proving to be an obstacle to attempts to reunify the two sides.
There are two separate issues in the Filioque controversy: the orthodoxy of the doctrine itself and the liceity of the interpolation of the phrase into the Nicene Creed. Although the debate over the orthodoxy of the doctrine preceded the question of the admissibility of the phrase as inserted into the Creed, the two issues became linked when the insertion received the approval of the pope in the eleventh century. After that point, the debate was no longer solely about the orthodoxy of the doctrine but also about the authority of the pope to define what was and was not orthodox. Anthony E. Siecienski writes that "[u]ltimately what was at stake was not only God's trinitarian nature, but also the nature of the Church, its teaching authority and the distribution of power among its leaders."
Hubert Cunliffe-Jones identifies two opposing views among Eastern Orthodox regarding the Filioque: a "liberal" view and a "rigorist" view. The "liberal" view sees the controversy as being largely a matter of mutual miscommunication and misunderstanding. In this view, both East and West are at fault for failing to allow for a "plurality of theologies". Each side went astray in considering their theological framework as the only one that was doctrinally valid and applicable. Thus, neither side would accept that the dispute was not so much about conflicting dogmas as it was about different theologoumena or theological perspectives. While all Christians must be in agreement on questions of dogma, there is room for diversity in theological approaches.