Filioque

Filioque, 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":

Καὶ εἰς τὸ Πνεῦμα τὸ Ἅγιον, τὸ κύριον, τὸ ζῳοποιόν, τὸ ἐκ τοῦ Πατρὸς ἐκπορευόμενον

(And in the Holy Spirit, the Lord, the giver of life, from the Father proceeding).

The Latin text speaks of the Holy Spirit as proceeding "from the Father and the Son".

Et in Spiritum Sanctum, Dominum, et vivificantem: qui ex Patre Filioque procedit

(And in the Holy Spirit, the Lord, and giver of life, who from the Father and the Son proceeds).

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 an obstacle to attempts to reunify the two sides.