Western addition to the Nicene creed.
We have seen[1] that the summary of Christian belief, known to us as the Nicene Creed, was completed at the Council of Constantinople, A.D. 381; but with this exception, that the article defining the faith of the Church concerning the Third Person of the Ever-Blessed Trinity, asserted only that "the Holy Ghost … proceedeth from the Father," without the addition of the words "and the Son;" and it was the controversy as to the admission or non-admission of these words into the Creed which caused the formal division between Eastern and Western Christendom. The question is said to have first arisen in the fifth century; and gradually the words in dispute came to be sung in the West during Divine Service. Decrees against it. In the ninth century an appeal was made on the subject to Pope Leo III., who decided in a provincial Council that no such addition could lawfully be made to the Creed, and ordered it to be engraved on silver plates exactly as the Council of Constantinople had left it. Towards the end of the same century another Council was held at Constantinople, which also decreed the disuse of the addition, and then the matter dropped for about a hundred and fifty years. Dispute stirred up again for political purposes. Its revival seems to have been chiefly owing to political jealousies and to the struggle for supremacy which was continually going on between Rome and Constantinople. We may be allowed to believe that the dispute was, in reality, a question of mere words, and that the two branches of the One Church did, and still do, hold the "One Faith," although differing in their mode of expressing it. Actual schism in consequence. Still the ultra-conservatism which has always distinguished the Eastern Church, and the unyielding temper which has been no less conspicuous in the Church of Rome, did in time bring about a formal schism; and in A.D. 1053, the Pope Leo IX. issued a sentence of excommunication against the Patriarch of Constantinople and all who adhered to him. In the following year the Patriarch Michael Cerularius summoned a synod at Constantinople, and retorted the excommunication upon the Latins. Two attempts at reconciliation were afterwards made, one in A.D. 1274, following the close of the last Crusade, and another which, after lengthened negotiations, came to an equally unsuccessful termination at the Council of Florence, A.D. 1430.
Outward union never since restored.
Since that time the two great Branches of the One Vine, whilst still drawing Life and Nourishment from the same Divine Root of Jesse by means of the same Holy Sacraments, have yet abstained from all acts of outward communion, and have failed to recognize in each other those essential marks of Catholicity which God's Mercy and Providence has preserved to them even in the midst of all their respective defects of Charity, or their errors in theory and practice.
[1] Chap. VI., sec. 3.