The addition may must be either a merely verbal additionmodification, or a fully verbal & and doctrinal additionmodification. If doctrinal, then it is either an extension of the truth, or a corruption of the truth. The Filioquist doctrine is filioque primarily a violates the canons by virtue of doctrinal violationdoctrine deviance, rather than linguisticvariance. The word was not included by the [[First Ecumenical Council|Council of Nicea]] nor of [[Second Ecumenical Council|Constantinople]]. But neither , nor was another phrase , "Deum de Deo" ("God from God"), which ; the latter was added to the Creed but is viewed accepted as orthodox, whereas the former was not.

Rome received the [[Fourth Ecumenical Council]], which referred to preceding councils, citing the authority of the text of the Creed. However, at this time, central Italy was in a state of collapse. In 410 and 455, Rome was vandalized and sacked by barbarian invasions. In 476, the Western Roman Empire fell, with the exile of Romulus Augustulus, the last emperor. Chaos followed.

After generations of social upheaval, strong leadership appeared in the person of Pepin the Short, king of the Franks, and his son, [[Charlemagne]], crowned as emperor in 800. Charlemagne intended to restore the Roman Empire in the West, with himself in charge, to the chagrin of the leaders of the Eastern Roman Empire. These he denigrated, whom he referred to as labelling them "Greeks" (and thus , by implication, not -Romans), despite the Roman capital being in the East and the continued use by Easterners of ''Roman'' to describe themselves. Charlemagne called for a council at Aix-la-Chapelle in 809 at which Pope [[Leo III of Rome|Leo III]] forbade the use of the ''filioque'' clause and ordered that the original version of the [[Nicene-Constantinopolitan Creed]] be engraved on silver tablets displayed at St. Peter's Basilica in Rome , apparently so that his conclusion would not be overturned in the future.

Some historians have suggested that the Franks in the 9th century pressured the Pope to adopt the ''filioque'' in order to drive a wedge between the Roman Church and the other patriarchates. It is true that Despite this action, the ''filioque'' had come into wide use in the West and was became widely thought to be an integral part of the Creed, while Rome, renowned for its stability in Orthodoxyand conservatism, resisted. Similarly, unleavened bread had come to be thought of as normative for the [[Eucharist]]; diocesan priests were expected to be unmarried. In such cases, in the West, ancient tradition was forgotten. Contemporary usage was thought to be normative and authentic. In these matters of discipline, the influence of the Franks is certain. They intended to exalt Charlemagne, as the new Roman Emperor. The Catholic religion, as they knew it, was to be part of the package. Meanwhile, from cac. 726 to 843, the Eastern Roman Empire, under the thumb of successive emperors, was dominated by the heresy of [[iconoclasm]]. Both Franks and Greeks, in their own way, departed from ancient tradition. Unlike the East, however, where iconoclasm was repudiated at the [[Seventh Ecumenical Council]] and the use of icons later confirmed by the [[Theodora (9th century empress)|Empress Theodora]], the West to date never recovered from its departure.

Within a couple of generations, in 858, a new situation came to pass. The Eastern Emperor Michael III removed [[Ignatius of Constantinople|Ignatius I]] as patriarch of Constantinople. The emperor replaced him with a layman, St. [[Photius the Great]], who was the first Imperial Secretary and Imperial Ambassador to Baghdad. However, Ignatius refused to abdicatebow to secular authority. Michael and Photius invited Pope [[Nicholas I of Rome]] to send legates to preside over a synod in Constantinople to settle the matter. With the council, the legates confirmed the patriarchate of Photius, much to Nicholas's chagrin, who then declared that they had "exceeded their authority."

In opposition to this removal of Ignatius, the bishop of Rome supported Ignatius as legitimate patriarch. Moreover, contrary in violation to existing canons, Photius had been ordained to the office of bishop very quickly. Some scholarship suggests that violation of these canons was the main reason the bishop of Rome rejected the appointment of Photius, though other major actions by Nicholas to bolster his power and position as pope puts his intervention in Eastern ecclesiastical matters more firmly in the context of his general programme of the growth of papal monarchy.

Therefore, after the arrival of an embassy from Ignatius, in 862, Nicholas said that Photius was deposed, as well as the bishop who ordained him and all the clergy Photius had appointed. The sheer temerity of this action did not even generate a response from Constantinople. However, several years later in 867, Photius finally rejected the Pope's assertion, particularly because of the activities of Latin missionaries in Bulgaria, who were, as St. Photius says, turning the Orthodox Christians there away from their pure Orthodox faith and leading them into [[heresy]]—most notably, the ''filioque''. Photius' response cited the ''filioque'' as proof that Rome had a habit of overstepping its proper limits.

In 867 and 869-70, synods in Rome and Constantinople (the [[Robber Council of 869-870]]) restored Ignatius to his position as patriarch and deposed Photius. In 877, after the death of Ignatius, Photius again resumed office, by order of the emperor and by the request of Ignatius himself, to whom Photius had been reconciled. In 879-880, he was officially restored to his see and the ''filioque'' effectively condemned by the [[Eighth Ecumenical Council]], a council at which papal legates participated and which the current pope, [[John VIII of Rome|John VIII]], eventually confirmed. He was deposed in 886 when Leo VI took over as emperor, who had had a dispute with his father and turned his animosity for his father toward one of his father's friends, Photius. Photius spent the rest of his life as a monk in exile in Armenia; he is revered by the Orthodox today as a [[saint]], one of the great [[Pillars of Orthodoxy]]. He was the first important [[theologian]] to accuse Rome of [[heresy]] in the matter of the ''filioque''.

In the thirteenth century, philosophical theologian and Roman saint Thomas Aquinas was one of the dominant Scholastic theologians. He dealt explicitly with the processions of the divine Persons in his ''Summa Theologica''. While the theology of Aquinas and other Scholastics was dominant in the Western Middle Ages, for all its apparent clarity and brilliance, it remains theology, not official [[Roman Catholic Church]] teaching.

The Crusaders in question were the Venetians of the [[Fourth Crusade]], who had earlier been excommunicated for attacking other Christians. In 1204, they were getting even for a avenging the slaughter of Venetian merchants, in rioting, that took place in 1182. Pope Innocent III had sent them a letter, asking them not to attack Constantinople; after hearing of the sack of the city, he lamented their action and disowned them. Nevertheless, the people of Constantinople had a deep hatred for the people they called the "Latins" or the "Franks," and of course the Western church's major "endowment" from the spoils carried away now still largely rests in the hands of the Vatican.

At the [[Council of Florence]] in 1439, Emperor [[John VIII Palaeologus]], Patriarch Joseph of Constantinople, and other bishops from the East travelled to northern Italy in hope of reconciliation with the West, mainly in order to solicit military assistance to fend off the encroaching Turkish invaders. After extensive discussion, in Ferrara, then in Florence, they acknowledged that some Latin Fathers spoke of the procession of the Spirit differently from the Greek Fathers. Since the general consensus of the Fathers was held to be reliable, as a witness to common faith, the Western usage was held not to be a heresy and not a barrier to restoration of full communion. All but one of the Orthodox Eastern patriarchs bishops present , but one, agreed and signed a decree of union between East and West, ''Laetentur Coeli'' in 1439. The one bishop who refused to sign and was later heralded as a Pillar of Orthodoxy by the Church was St. [[Mark of Ephesus]], who followed in the footsteps of the previous Pillar of Orthodoxy, St. [[Photius the Great]].

Officially and publicly, Rome the Roman and the Orthodox Church were back in communion. However, the reconciliation achieved at Florence was soon destroyed, founded as it was on a compromise of faith. Numerous Orthodox faithful and bishops rejected the union, saying that the council's teachings were incorrect and therefore not ecumenical. Moreover, after the Turks [[Fall of Constantinople|conquered Constantinople in 1453]], they fostered separation from the West, which remained an adversary to Islamic political and military dominance. Furthermore, the patriarch, Gennadius, was also one of the bishops who had repudiated the reunion of Florence on his own initiative.