The Creed set forth at Constantinople in 381 says that the Holy Spirit "proceeds from the Father", words drawn from Christ's own promise in John 15:26. In the Latin West the word filioque, "and the Son", was later added, so that the Western Creed says the Spirit proceeds from the Father and the Son.
The addition was first made at the Third Council of Toledo, in Spain, in 589, against the Arians. Its use spread in the Frankish church in the eighth century, and in 1014, under pressure from the Emperor Henry II, Pope Benedict VIII brought it into the Creed used at Rome. Together with the question of the pope's authority, it became one of the chief causes of the Great Schism of 1054.
The Orthodox Church objects on two grounds. The first is the Creed itself: it was given by councils of the whole Church, and the Orthodox Church holds that the Council of Ephesus in 431 forbade any change to it, so no one church may add to it. The second is the teaching: with the Fathers, the Orthodox Church confesses the Father as the one source of the Son and of the Spirit.
The Catholic Church, for its part, also holds the Father to be the "principle without principle" and first origin of the Spirit, and the Second Council of Lyon taught that the Spirit proceeds from the Father and the Son "not as from two principles" but from one. It encourages the Eastern Catholic Churches to omit the filioque from the Creed.
Both churches accept St Maximus the Confessor, and his writings have been offered as common ground. The question remains a point of disagreement between East and West, and it is still discussed between them.
