The East–West Schism, also called the Great Schism and the Schism of 1054, was the break of communion between what are now the Catholic Church and Eastern Orthodox Churches, which had lasted until the 11th century.^[6] The Schism was the culmination of theological and political differences between the Christian East and West which had developed over the preceding centuries.

A succession of ecclesiastical differences and theological disputes between the Greek East and Latin West pre-dated the formal rupture that occurred in 1054.^[7][8][9] Prominent among these were the issues of the procession of the Holy Spirit, whether leavened or unleavened bread should be used in the Eucharist,^[1] the Bishop of Rome's claim to universal jurisdiction, and the place of the See of Constantinople in relation to the Pentarchy.^[13]

In 1053, the first step was taken in the process which led to formal schism: the Greek churches in southern Italy were forced either to close or to conform to Latin practices.^[14][15][16] In retaliation, the Ecumenical Patriarch of Constantinople Michael I Cerularius ordered the closure of all Latin churches in Constantinople. In 1054, the papal legate sent by Leo IX travelled to Constantinople for purposes that included refusing to Cerularius the title of "Ecumenical Patriarch" and insisting that he recognize the Pope's claim to be the head of all the churches.^[7] The main purpose of the papal legation was to seek help from the Byzantine Emperor in view of the Norman conquest of southern Italy and to deal with recent attacks by Leo of Ohrid against the use of unleavened bread and other Western customs,^[17] attacks that had the support of Cerularius. Historian Axel Bayer says the legation was sent in response to two letters, one from the Emperor seeking assistance in arranging a common military campaign by the eastern and western empires against the Normans, and the other from Cerularius.^[18] On the refusal of Cerularius to accept the demand, the leader of the legation, Cardinal Humbert of Silva Candida, O.S.B., excommunicated him, and in return Cerularius excommunicated Humbert and the other legates.^[7] This was only the first act in a centuries-long process that eventually became a complete schism.^[19]

The validity of the Western legates' act is doubtful, since Pope Leo had died and Cerularius' excommunication applied only to the legates personally.^[7] Still, the Church split along doctrinal, theological, linguistic, political, and geographical lines, and the fundamental breach has never been healed, with each side sometimes accusing the other of having fallen into heresy and of having initiated the division. The Latin led Crusades, the Massacre of the Latins in 1182, the West's retaliation in the Sacking of Thessalonica in 1185, the capture and pillaging of Constantinople by the Fourth Crusade in 1204, and the imposition of Latin patriarchs made reconciliation more difficult.^[7] Establishing Latin hierarchies in the Crusader states meant that there were two rival claimants to each of the patriarchal sees of Antioch, Constantinople, and Jerusalem, making the existence of schism clear.^[20] Several attempts at reconciliation did not bear fruit. In 1965, Pope Paul VI and the Ecumenical Patriarch of Constantinople Athenagoras I nullified the anathemas of 1054,^[7] although this nullification of measures taken against a few individuals was essentially a goodwill gesture and did not constitute any sort of reunion.^[21] Contacts between the two sides continue: every year a delegation from each joins in the other's celebration of its patronal feast, Saints Peter and Paul (29 June) for Rome and Saint Andrew (30 November) for Constantinople, and there have been a number of visits by the head of each to the other. The efforts of the Ecumenical Patriarchs towards reconciliation with the Catholic Church have often been the target of sharp criticism from some fellow Orthodox.^[22]

The schism between the Western and Eastern Mediterranean Christians resulted from a variety of political, cultural and theological factors which transpired over centuries.^[23] Historians regard the mutual excommunications of 1054 as the terminal event.^[24] It is difficult to agree on an exact date for the event where the start of the schism was apparent.^[25] It may have started as early as the^[26] Quartodeciman controversy at the time of Victor of Rome (c. 180). Orthodox apologists point to this incident as an example of claims by Rome to papal primacy and its rejection by Eastern Churches.

Sporadic schisms in the common unions took place under Pope Damasus I in the 4th and 5th centuries.^[27][28][29] Disputes about theological and other questions led to schisms between the Churches in Rome and Constantinople for 37 years from 482 to 519 (the Acacian Schism). Most sources agree that the separation between East and West is clearly evident by the Photian schism for 4 years from 863–867.^{[30] [31]}

Apart from Rome in the West, "many major Churches of the East claim to have been founded by the apostles: Antioch by Peter and Paul, Alexandria by Mark, Constantinople by Andrew, Cyprus by Barnabas, Ethiopia by Matthew, India by Thomas, Edessa in eastern Syria by Thaddeus, Armenia by Bartholomew, Georgia by Simon the Zealot."^[32] Famous also are the seven churches of Asia (the Roman province of Asia), mentioned in the opening chapters of the Book of Revelation.

While the church at Rome claimed a special authority over the other churches, the extant documents of that era yield "no clear-cut claims to, or recognition, of papal primacy."^[33][34]

Towards the end of the 2nd century, Victor, the Bishop of Rome, attempted to resolve the Quartodeciman controversy. The question was whether to celebrate Easter concurrently with the Jewish Passover, as Christians in the Roman province of Asia did, or to wait until the following Sunday, as was unanimously decreed by synods held in other Eastern provinces, such as those of Palestine and Pontus, the acts of which were still extant at the time of Eusebius, and in Rome.^[35][36] The pope attempted to excommunicate the churches in Asia, which refused to accept the observance on Sunday. Other bishops rebuked him for doing so.^[37] Laurent Cleenewerck comments:

Despite Victor's failure to carry out his intent to excommunicate the Asian churches, many Catholic apologists point to this episode as evidence of papal primacy and authority in the early Church, citing the fact that none of the bishops challenged his right to excommunicate but rather questioned the wisdom and charity of his action.^[38]

The opinion of the Bishop of Rome was often sought, especially when the patriarchs of the Eastern Mediterranean were locked in fractious dispute. However, the Bishop of Rome's opinion was by no means accepted automatically. The bishops of Rome never obviously belonged to either the Antiochian or the Alexandrian schools of theology, and usually managed to steer a middle course between whatever extremes were being propounded by theologians of either school. Because Rome was remote from the centres of Christianity in the eastern Mediterranean, it was frequently hoped its bishop would be more impartial. For instance, in 431, Cyril, the patriarch of Alexandria, appealed to Pope Celestine I, as well as the other patriarchs, charging Constantinople Patriarch Nestorius with heresy, which was dealt with at the Council of Ephesus.

In 342, Pope Julius I wrote: "The custom has been for word to be written first to us [in the case of bishops under accusation, and notably in apostolic churches], and then for a just sentence to be passed from this place".^[39]

In 382 a synod in Rome protested against the raising of Constantinople to a position above that of Alexandria, and spoke of Rome as "the apostolic see".^[40] Pope Siricius (384–399) claimed for papal decretals the same binding force as decisions of synods, Pope Innocent I (401–417) said that all major judicial cases should be reserved for the see of Rome, and Pope Boniface I (418–422) declared that the church of Rome stands to "the churches throughout the world as the head to its members" and that bishops everywhere, while holding the one same episcopal office, must "recognise those to whom, for the sake of ecclesiastical discipline, they should be subject".^[41] Celestine I (r. 422–432) considered that the condemnation of Nestorius by his own Roman synod in 430 was sufficient, but consented to the general council as "of benefit in manifesting the faith".^[42] Pope Leo I and his successors rejected canon 28 of the Council of Chalcedon, as a result of which it was not officially recorded even in the East until the 6th century.^[43][44] The Acacian schism (484–519), when, "for the first time, West lines up against East in a clear-cut fashion",^[45] ended with acceptance of a declaration insisted on by Pope Hormisdas (514–523) that "I hope I shall remain in communion with the apostolic see in which is found the whole, true, and perfect stability of the Christian religion".^[46][47][48] Earlier, in 494, Pope Gelasius I (492–496) wrote to Byzantine Emperor Anastasius, distinguishing the power of civil rulers from that of the bishops (called "priests" in the document), with the latter supreme in religious matters; he ended his letter with: "And if it is fitting that the hearts of the faithful should submit to all priests in general who properly administer divine affairs, how much the more is obedience due to the bishop of that see which the Most High ordained to be above all others, and which is consequently dutifully honoured by the devotion of the whole Church."^[49] Pope Nicholas I (858–867) made it clear that he believed the power of the papacy extended "over all the earth, that is, over every church".^[50][51]

In 330, Emperor Constantine moved the imperial capital to Byzantium, a strategically located city on the Bosporus. He renamed the capital Nova Roma ("New Rome"), but the city would become known as Constantinople.^[52] The centre of gravity in the empire was fully recognised to have completely shifted to the eastern Mediterranean. Rome lost the Senate to Constantinople and lost its status and gravitas as imperial capital.^[53]

The bishop of Byzantium was under the authority of the metropolitan of Heraclea when in 330 Roman Emperor Constantine I moved his residence to this town, which, rebuilt on a larger scale, became known as Constantinople.^[54] Thereafter, the bishop's connection with the imperial court meant that he was able to free himself from ecclesiastical dependency on Heraclea and in little more than half a century to obtain recognition of next-after-Rome ranking from the First Council of Constantinople (381), held in the new capital. No Western bishop took part in this council, and the Latin Church recognized it as ecumenical only in the mid-6th century.^[55] It decreed: "The Bishop of Constantinople, however, shall have the prerogative of honour after the Bishop of Rome; because Constantinople is New Rome",^[56] thus raising it above the sees of Alexandria and Antioch. This has been described as sowing the seed for the ecclesiastical rivalry between Constantinople and Rome that was a factor leading to the schism between East and West.^[57][58] The website of the Orthodox Church in America says that the Bishop of Byzantium was elevated to Patriarch already in the time of Constantine.^[59]

Disunion in the Roman Empire contributed to disunion in the Church. Theodosius the Great, who in 380 established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following the death of Theodosius in 395, the Empire was divided for the final time into western and eastern halves. In the 4th century, the Roman emperor (reigning in Constantinople) started to control the Church in his territory.^[60]

The patriarchs of Constantinople often tried to adopt an imperious position over the other patriarchs, provoking their resistance. For example, in 431 Patriarch Cyril, of Alexandria, impeached for heresy, Patriarch Nestorius, of Constantinople.^[61][61]

Alexandria's objections to Constantinople's promotion, which led to a constant struggle between the two sees in the first half of the 5th century,^[62] were supported by Rome, which proposed the theory that the most important sees were the three Petrine ones, of Rome, Antioch, and Alexandria,^[63] with Rome in first place.^[55]

However, the power of the patriarch of Constantinople continued to grow.^[64] Eastern Orthodox state that the 28th canon of the Council of Chalcedon (451)^[65] explicitly proclaimed the equality of the Bishops of Rome and Constantinople,^[66][67] and that it established the highest court of ecclesiastical appeal in Constantinople.^[65] The patriarch of the imperial capital succeeded in his efforts^[68] to become the leading bishop in the Byzantine Empire: he "headed a vast curia and other bishops who resided in Constantinople constituted a permanent synod, which became the real governing body of the church".^[69]

Patriarch John IV of Constantinople, who died in 595, assumed the title of "Ecumenical Patriarch".^[43]

The idea that with the transfer of the imperial capital from Rome to Constantinople, primacy in the Church was also transferred, is found in undeveloped form as early as John Philoponus (c. 490 – c. 570). It was enunciated in its most advanced form by Photios I of Constantinople (c. 810 – c. 893). Constantinople, as the seat of the ruler of the empire and therefore of the world, was the highest among the patriarchates and, like the emperor, had the right to govern them.^[70]

After the Roman Emperor Constantine the Great legalized Christianity (with the Edict of Milan), he summoned the First Ecumenical Council at Nicaea in 325. The bishops at the council confirmed the position of the metropolitan sees of Rome and Alexandria as having authority outside their own province, and also the existing privileges of the churches in Antioch and the other provinces.^[71] These sees were later called Patriarchates. These were given an order of precedence: Rome, as capital of the empire was naturally given first place, then came Alexandria and Antioch. In a separate canon the Council also approved the special honor given to Jerusalem over other sees subject to the same metropolitan.^[72]

Roman dominate Emperor Theodosius I convened the second ecumenical council (Constantinople I) at the imperial capital city in 381. The council elevated the see of Constantinople, to a position ahead of the other chief metropolitan sees, except that of Rome thus raising it above the sees of Alexandria and Antioch.^[2] This action has been described as sowing the seed for the ecclesiastical rivalry between Constantinople and Rome which was ultimately a factor leading to the schism between East and West.^[74][75][3] It demarcated the territory within the praetorian prefecture of the East into five canonical territories corresponding to the five civil dioceses: Diocese of Egypt (metropolis in Alexandria), Diocese of the East (metropolis in Antioch), Diocese of Asia (Metropolis of Ephesus), Diocese of Pontus (metropolis in Caesarea Cappadociae), and Diocese of Thrace (metropolis in Heraclea, later under Constantinople);^[55][77] The council mentioned the churches in the civil dioceses of Asia, Pontus, and Thrace, it decreed that the synod of each province should manage the ecclesiastical affairs of that province alone, except for the privileges already recognized for sees of Alexandria and Antioch.^[77]

No Western bishops attended the council and no legate of the bishop of Rome was present.^[78] The Latin Church recognized the council as ecumenical about 150 years later,^[78] in the mid-6th century.^[55][76]

Rome's Tome of Leo (449) was highly regarded, and formed the basis for the Council of Chalcedon formulation. But it was not universally accepted and was even called "impious" and "blasphemous" by those who condemned the council that approved and accepted it.^[79] The next ecumenical council corrected a possible imbalance in Pope Leo's presentation. Although the Bishop of Rome was well respected even at this early date, the East holds that the concept of the primacy of the Roman See and Papal Infallibility were only developed much later.

The disputed^[43][80] canon 28 of the Council of Chalcedon in 451, confirming the authority already held by Constantinople, granted its archbishop jurisdiction over Pontus and Thrace.^[81]

The council also ratified an agreement between Antioch and Jerusalem, whereby Jerusalem held jurisdiction over three provinces,^[82] numbering it among the five great sees.^[83] As thus interpreted, there were now five patriarchs presiding over the Church within the Byzantine Empire, in the following order of precedence: the Patriarch of Rome, the Patriarch of Constantinople, the Patriarch of Alexandria, the Patriarch of Antioch and the Patriarch of Jerusalem.

Although Leo I, whose delegates were absent when this resolution was passed, recognized the council as ecumenical and confirmed its doctrinal decrees, he rejected its canon 28 on the ground that it contravened the sixth canon of Nicaea and infringed the rights of Alexandria and Antioch.^[55][84] However, by that time Constantinople, the permanent residence of the emperor, had in reality enormous influence, and had it not been for the opposition of Rome, its bishop could easily have been given first place among all the bishops.^[55]

This canon would remain a constant source of friction between East and West, until the mutual excommunications of 1054 made it irrelevant in that regard;^[85] but controversy about its applicability to the authority of the patriarchate of Constantinople still continues.^[86]

The same disputed canon also recognized an authority of Constantinople over bishops of dioceses "among the barbarians", which has been variously interpreted as referring either to all areas outside the Byzantine Empire or only to those in the vicinity of Pontus, Asia and Thrace or to non-Greeks within the empire.^[43]

Canon 9 of the Council also declared: "If a bishop or clergyman should have a difference with the metropolitan of the province, let him have recourse to the Exarch of the Diocese, or to the throne of the Imperial City of Constantinople, and there let it be tried." This has been interpreted as conferring on the see of Constantinople a greater privilege than what any council ever gave Rome,^[87] or as of much lesser significance than that.^[88][89]

After the Council of Chalcedon (451), the position of the Patriarchate of Alexandria was weakened by a division in which the great majority of its Christian population followed the form of Christianity that its opponents called Monophysitism.^[55]

In 476, when the last emperor of the western part of the Roman Empire was deposed and the western imperial insignia were sent to Constantinople, there was once again a single Roman Emperor. However, he had little power in the West, which was ruled almost entirely by various Germanic tribes. In the opinion of Randall R. Cloud, the permanent separation of the Greek East from the Latin West was "the fundamental reason for the estrangement that soon followed between the Greek and the Latin Christians".^[90]

The dominant language of the West was Latin, while that of the East was Greek. Soon after the fall of the West to invaders, the number of individuals who spoke both languages dwindled, and communication between East and West grew much more difficult. With linguistic unity gone, cultural unity began to crumble as well. The two-halves of the Church were naturally divided along similar lines; they developed different rites and had different approaches to religious doctrines. Although the schism was still centuries away, its outlines were already perceptible.^[91]

In the areas under his control, Justinian I established caesaropapism as the constitution of the Church in a scheme according to which the emperor "had the right and duty of regulating by his laws the minutest detail of worship and discipline, and also of dictating the theological opinions to be held in the Church".^[92] According to the Westminster Dictionary of Theological Terms, this caesaropapism was "a source of contention between Rome and Constantinople that led to the schism of 1054".^[93] Explicit approval of the emperor in Constantinople was required for consecration of bishops within the empire. During the period called the Byzantine Papacy, this applied to the bishops of Rome, most of whom were of Greek or Syrian origin. Resentment in the West against the Byzantine emperor's governance of the Church is shown as far back as the 6th century, when "the tolerance of the Arian Gothic king was preferred to the caesaropapist claims of Constantinople".^[94] The origins of the distinct attitudes in West and East are sometimes traced back even to Augustine of Hippo, who "saw the relationship between church and state as one of tension between the 'city of God' and the 'city of the world'", and Eusebius, who "saw the state as the protector of the church and the emperor as God's vicar on earth".^[95]

By 661, Muslim Arabs had taken over the territories assigned to the patriarchates of Alexandria, Antioch and Jerusalem, which thereafter were never more than partially and temporarily recovered. In 732, Emperor Leo III the Isaurian, in revenge for the opposition of Pope Gregory III to the emperor's iconoclast policies, transferred Sicily, Calabria and Illyria from the patriarchate of Rome (whose jurisdiction until then extended as far east as Thessalonica) to that of Constantinople.^[96] The Constantinople patriarchate, after expanding eastward at the time of the Council of Chalcedon to take in Pontus and the Roman province of Asia, which at that time were still under the emperor's control, thus expanded equally to the west, and was practically coextensive with the Byzantine Empire.

The West's rejection of the Quinisext Council of 692 led to pressure from the Eastern Empire on the West to reject many Latin customs as non-Orthodox. The Latin practices that had got the attention of the other Patriarchates and that had been condemned by this Council included the practice of celebrating Mass on weekdays in Lent (rather than having Pre-Sanctified Liturgies);^[97] fasting on Saturdays throughout the year;^[98] omitting the "Alleluia" in Lent; depicting Christ as a lamb;^[99] using unleavened bread.^[100] Larger disputes were revealed regarding Eastern and Western attitudes toward celibacy for priests and deacons, with the Council affirming the right of married men to become priests (though forbidding priests to marry and forbidding bishops to live with their wives)^[101][102] and prescribing deposition for anyone who attempted to separate a clergyman other than a bishop from his wife, or for any cleric other than a bishop who dismissed his wife.^[103]

Pope Sergius I, who was of Syrian ancestry, rejected the council.^[104] Emperor Justinian II ordered his arrest.^[105] This was thwarted.^[106][107]

In 694, in Visigothic Spain, the council was ratified by the Eighteenth Council of Toledo at the urging of the king, Wittiza.^[108] Fruela I of Asturias reversed the decision of Toledo sometime during his reign (757–768).^[108]

The primary causes of the schism were disputes over conflicting claims of jurisdiction, in particular over papal authority—Pope Leo IX claimed he held authority over the four Eastern patriarchs—and over the insertion of the Filioque clause into the Nicene Creed by the Western patriarch in 1014.^[109] Eastern Orthodox today state that Council of Chalcedon canon 28 explicitly proclaimed the equality of the Bishops of Rome and Constantinople and that it established the highest court of ecclesiastical appeal in Constantinople.^[110] Council of Ephesus canon 7 declared:

Eastern Orthodox today state that this canon of the Council of Ephesus explicitly prohibited modification of the Nicene Creed drawn up by the first Ecumenical Council in 325, the wording of which, it is claimed, but not the substance, had been modified by the second Ecumenical Council, making additions such as "who proceeds from the Father".

Eastern Orthodox argue that First Council of Ephesus canon 7 explicitly prohibited modification of the Nicene Creed by any man (not by ecumenical church council) drawn up by the first Ecumenical Council in 325.^[112] In reality, the Council made no exception for an ecumenical council or any other body of bishops,^[113] and the Greeks participating in the Council of Florence emphatically denied that even an ecumenical council had the power to add anything to the creed.^[114] The creed quoted in the Acts of the Council of Ephesus of 431 (the third ecumenical council) is that of the first ecumenical council, that of Nicaea (325), without the modifications that the second ecumenical council, held in Constantinople in 381, is understood to have made to it, such as the addition of "who proceeds from the Father".^[115][116] Eastern Orthodox theologians state this change of the wording of the churches' original creed, was done to address various teachings outside of the church in specific the Macedonius I of Constantinople teaching which the council claimed was a distortion of the church's teaching on the Holy Spirit. This was not a change of the orthodoxy of the churches' original creed.^[117] Thus the word ἑτέραν in the seventh canon of the later Council of Ephesus is understood as meaning "different" or "contradictory" and not "another" in the sense of mere explanatory additions to the already existing creed.^[114] Some scholars hold that the additions attributed to the First Council of Constantinople were adopted only with the 451 Council of Chalcedon, 20 years after that of Ephesus,^[118][119] and even that the Council of Ephesus, in which Alexandrian influence was dominant, was by this canon excluding the Constantinopolitan Creed, which eventually annexed the name and fame of the creed adopted at Nicaea.^[120]

Many other issues increased tensions.

In Eastern Christendom, the teaching of papal supremacy is said to be based on the pseudo-Isidorian Decretals,^[135] documents attributed to early popes but actually forged, probably in the second quarter of the 9th century, with the aim of defending the position of bishops against metropolitans and secular authorities. The Orthodox East contests the teaching that Peter was the Patriarch of Rome, a title that the West too does not give him. Early sources such as St. Irenaeus can be interpreted as describing Pope Linus as the first bishop of Rome and Pope Cletus the second. The Oxford Dictionary of Popes states: "In the late 2nd or early 3rd cent. the tradition identified Peter as the first bishop of Rome. This was a natural development once the monarchical episcopate, i.e. government of the local church by a single bishop, as distinct from a group of presbyter bishops, finally emerged in Rome in the mid-2nd cent. The earlier tradition, however, which placed Peter and Paul in a class apart as the pioneers who together established the Roman church and its ministry, was never lost sight of."^[136] St. Peter was according to tradition bishop of Antioch at one point, and was then succeeded by Evodius and Ignatius. The Eastern Orthodox do not hold the primacy of the Pope of Rome over the Eastern church; they teach that the Pope of Rome is the first among equals. The first seven Ecumenical Councils were held in the East and called by the Eastern Emperors, Roman pontiffs never presided over any of them.^[137]

Three councils were held, two by Constantinople, one by Rome.^[138] Rome attempted to replace a seated Patriarch with one amenable to the Filioque dispute. The Orthodox responded by denouncing the replacement and excommunicating the pope convening the Roman council, denouncing the pope's attempt to control affairs outside the purview of Rome, and denouncing the addition of Filioque as a heresy. Each church recognizes its own council(s) as legitimate and does not recognize the other's council(s).^{[139][140][141][140][142][141][143][144]}

In 1053 Leo of Ohrid, at the instigation, according to J. B. Bury, of Patriarch Michael Cerularius of Constantinople,^[145] wrote to Bishop John of Trani a letter, intended for all the Latin bishops, including the pope, in which he attacked Western practices such as using unleavened bread for the Eucharist, and fasting rules that differed from those in Constantinople, while Cerularius himself closed all Latin churches in Constantinople.

In response, Leo IX wrote the letter In terra pax of 2 September 1053,^[146] addressed to Cerularius and Leo of Ohrid, in which he speaks at length of the privileges granted through Saint Peter to the see of Rome. In one of the 41 sections of his letter he also speaks of privileges granted by the emperors, quoting from the Donation of Constantine document, which he believed to be genuine (section 20).^[147] Some scholars say that this letter was never actually dispatched, but was set aside, and that the papal reply actually sent was the softer but still harsh letter Scripta tuae of January 1054.^[148]

The advance of the Norman conquest of southern Italy constituted a threat to the possessions of both the Byzantine Empire and the papacy, each of which sought the support of the other. Accordingly, conciliatory letters, the texts of which have not been preserved, were written to the pope by the emperor and Cerularius. In his January 1054 reply to the emperor, Quantas gratias,^[149] Leo IX asks for his assistance against the Normans and complains of what the pope saw as Caerularius's arrogance. In his reply to Caerularius,^[150] he upbraided the patriarch for trying to subject the patriarchs of Alexandria and Antioch to himself and for adopting the title of Ecumenical Patriarch, and insisted on the primacy of the see of Rome.^[147]

These two letters were entrusted to a delegation of three legates, headed by the undiplomatic cardinal Humbert of Silva Candida, and also including Frederick of Lorraine, who was papal secretary and Cardinal-Deacon of Santa Maria in Domnica, and Peter, Archbishop of Amalfi. They were given friendship and support by the emperor but were spurned by the patriarch. Finally, on 16 July 1054, three months after Pope Leo's death in April 1054 and nine months before the next pope took office,^[148] they laid on the altar of Hagia Sophia, which was prepared for celebration of the Divine Liturgy, a bull of excommunication of Cerularius and his supporters. At a synod held on 20 July 1054, Cerularius in turn excommunicated the legates.^[147][154] In reality, only Michael may have been excommunicated along with his then-living adherents.^[4]

At the time of the excommunications, many contemporary historians, including Byzantine chroniclers, did not consider the event significant.^{[156][157][158][159]}

Efforts were made in subsequent centuries by emperors, popes and patriarchs to heal the rift between the churches. However, a number of factors and historical events worked to widen the separation over time.^[160]

"Even after 1054 friendly relations between East and West continued. The two parts of Christendom were not yet conscious of a great gulf of separation between them. … The dispute remained something of which ordinary Christians in East and West were largely unaware".^[161]

There was no single event that marked the breakdown. Rather, the two churches slid into and out of schism over a period of several centuries, punctuated with temporary reconciliations.

Starting from the late 11th century, dependency of Byzantine Empire on the naval forces of Republic of Venice and, to a lesser extent, Republic of Genoa and Republic of Pisa led to predominance of Catholic merchants in Byzantium (they were getting major trading concessions starting from the 1080s), subsequently causing economic and social upheaval. Together with the perceived arrogance of the Italians, it fueled popular resentment amongst the middle and lower classes both in the countryside and in the cities.^[162]

By the second half of the 12th century practically uncontrollable rivalry between competitors from different city states made it to Italians raiding quarters of other Italians in the capital, and retaliatory draconian measures by the Byzantine authorities led to subsequent deterioration of inter-religious relations in the city.

When in 1182 regency of empress mother Maria of Antioch, an ethnical French notorious for the favoritism shown to Latin merchants and the big aristocratic land-owners, was deposed by Andronikos I Komnenos on the wake of popular support, the new emperor allowed mobs to massacre hated foreigners. Henceforth Byzantine foreign policy was invariably perceived as sinister and anti-Latin in the West.^[163]

In the course of the Fourth Crusade of 1202–1204 Latin crusaders and Venetian merchants sacked Constantinople itself (1204), looting the Church of Holy Wisdom and various other Orthodox holy sites,^[164] and converting them to Latin Catholic worship. The Norman Crusaders also destroyed the Imperial Library of Constantinople.^{[165][166][167]} Various holy artifacts from these Orthodox holy places were taken to the West. The crusaders also appointed a Latin Patriarch of Constantinople.^[164] The conquest of Constantinople and the final treaty established the Latin Empire of the East and the Latin Patriarch of Constantinople (with various other Crusader states). Later some religious artifacts were sold in Europe to finance or fund the Latin Empire in Byzantium – as when Emperor Baldwin II of Constantinople (r. 1228–1261) sold the relic of the Crown of Thorns while in France trying to raise new funds to maintain his hold on Byzantium.^[168] In 1261 the Byzantine Emperor Michael VIII Palaiologos brought the Latin Empire to an end. However, the Western attack on the heart of the Byzantine Empire is seen as a factor that led eventually to its conquest by Ottoman Muslims in the 15th century.

In northern Europe, the Teutonic Knights, after their 12th- and 13th-century successes in the Northern Crusades,^[169] attempted (1240) to conquer the Eastern Orthodox Russian Republics of Pskov and Novgorod, an enterprise endorsed by Gregory IX^[169] (Pope from 1227 to 1241). One of the major defeats the Teutonic Knights suffered was the Battle of the Ice in 1242. Catholic Sweden also undertook several campaigns against Orthodox Novgorod. There were also conflicts between Catholic Poland and Orthodox Russia. Such conflicts solidified the schism between East and West.

The Second Council of Lyon was convoked to act on a pledge by Michael VIII to reunite the Eastern church with the West.^[170] Wishing to end the Great Schism that divided Rome and Constantinople, Gregory X had sent an embassy to Michael VIII, who had reconquered Constantinople, putting an end to the remnants of the Latin Empire in the East, and he asked Latin despots in the East to curb their ambitions.

On 29 June (Feast of Saints Peter and Paul patronal feast of Popes), Gregory X celebrated a Mass in St John's Church, where both sides took part. The council declared that the Roman church possessed "the supreme and full primacy and authority over the universal Catholic Church."

The union effected was "a sham and a political gambit", a fiction maintained by the emperor to prevent westerners from recovering the city of Constantinople, which they had lost just over a decade before, in 1261.^{[171][172][173]} It was fiercely opposed by clergy and people^[174][175] and never put into effect,^[176] in spite of a sustained campaign by Patriarch John XI of Constantinople (John Bekkos), a convert to the cause of union, to defend the union intellectually, and vigorous and brutal repression of opponents by Michael.^[174][177] In 1278 Pope Nicholas III, learning of the fictitious character of Greek conformity,^[173] sent legates to Constantinople, demanding the personal submission of every Orthodox cleric and adoption of the Filioque,^[178] as already the Greek delegates at Lyon had been required to recite the Creed with the inclusion of Filioque and to repeat it two more times.^[179] Emperor Michael's attempts to resolve the schism ended when Pope Martin IV, seeing that the union was only a sham, excommunicated Michael VIII 1281 in support of Charles of Anjou's attempts to mount a new campaign to retake the Eastern Roman provinces lost to Michael.^{[174][180][181][182][183][184][185][186]} Michael VIII's son and successor Andronicus II repudiated the union, and Bekkos was forced to abdicate, being eventually exiled and imprisoned until his death in 1297.

In the 15th century, the eastern emperor John VIII Palaiologos, pressed hard by the Ottoman Turks, was keen to ally himself with the West, and to do so he arranged with Pope Eugene IV for discussions about reunion to be held again, this time at the Council of Ferrara-Florence. After several long discussions, the emperor managed to convince the Eastern representatives to accept the Western doctrines of Filioque, Purgatory and the supremacy of the Papacy. On 6 June 1439 an agreement was signed by all the Eastern bishops present but one, Mark of Ephesus, who held that Rome continued in both heresy and schism. It seemed that the Great Schism had been ended. However, upon their return, the Eastern bishops found their agreement with the West broadly rejected by the populace and by civil authorities (with the notable exception of the Emperors of the East who remained committed to union until the Fall of Constantinople two decades later). The union signed at Florence has never been accepted by the Eastern churches.

In May 1453, the capital of the Eastern Roman Empire fell to the invading Ottoman Empire. But Orthodox Christianity was already entrenched in Russia, whose political and de facto religious centre had shifted from Kiev to Moscow. The Russian Church, a part of the Church of Constantinople until the mid-15th century, was granted full independence (autocephaly) and elevated to the rank of Patriarchate in 1589. The Russian political and ecclesiastical elite came to view Moscow as the Third Rome, a legitimate heir to Constantinople and Byzantium.^[187]

Under Ottoman rule, the Orthodox Church acquired the status of an autonomous millet, specifically the Rum Millet. The Ecumenical Patriarch became the ruler (millet başı) of all the Orthodox Christian subjects of the empire, including non-Greeks. Upon conquering Constantinople, Mehmed II assumed the legal function of the Byzantine Emperors and appointed Patriarch Gennadius II. The sultans enhanced the temporal powers of the Greek orthodox hierarchy that came to be politically beholden solely to the Ottoman sultan and, along with other Ottoman Greek nobles, came to run the Balkan Orthodox domains of the Ottoman Empire. As a result, the entire Orthodox communion of the Balkans and the Near East became isolated from the rest of Christendom. For the next four hundred years, it would be confined within the Islamic world, with which it had little in common religiously or culturally.

In Russia, the anti-Catholic sentiments came to be entrenched by the Polish intervention during the Time of Troubles in the early 17th century, which was seen as an attempt to convert Moscow to Catholicism. The modern Russian national holiday, Unity Day, was established on the day of church celebration in honour of the Our Lady of Kazan icon, which is believed to have miraculously saved Moscow from outright Polish conquest in 1612. Patriarch Hermogenes of Moscow was martyred by the Poles and their supporters during this period (see also Polish–Lithuanian–Muscovite Commonwealth).^[188][189]

The doctrine of papal primacy was further developed at the First Vatican Council, which declared that "in the disposition of God the Roman church holds the preeminence of ordinary power over all the other churches". This council also affirmed the dogma of papal infallibility, declaring that the infallibility of the Christian community extends to the pope himself, when he defines a doctrine concerning faith or morals to be held by the whole Church. These new dogma, as well as the dogma of the Immaculate Conception promulgated in Ineffabilis Deus a few years prior, are unequivocally rejected by the Eastern Church as heretical.^[190]

A major event of the Second Vatican Council (Vatican II), was the issuance by Pope Paul and Orthodox Patriarch Athenagoras I of Constantinople of the Catholic–Orthodox Joint Declaration of 1965. At the same time, they lifted the mutual excommunications dating from the 11th century.^[191] The act did not result in restoration of communion.

The Eastern Catholic Churches, historically referred to as ″uniate″ by the Orthodox, consider themselves to have reconciled the East and West Schism by having accepted the primacy of the Bishop of Rome while retaining some of the canonical rules and liturgical practices in line with the Eastern tradition such as the Byzantine Rite that is prevalent in the Orthodox Churches. Some Eastern Orthodox charge that joining in this unity comes at the expense of ignoring critical doctrinal differences and past atrocities.

There have been periodic conflicts between the Orthodox and Eastern Catholics in Ukraine and Belarus, then under Polish rule,^[192] and later also in Transylvania (see the Romanian Greek Catholic Church United with Rome). Pressure and government-sponsored reprisals were used against Eastern Catholic Churches such as the Ukrainian Greek Catholic Church in the Russian Empire and later in the USSR.^[193] Since the late 1980s, the Moscow Patriarchate (the Russian Orthodox Church) has criticised the methods of restoration of the ″uniate″ church structures in Ukraine as well as what it called Catholic proselytism in Russia.^[194]

In 1993, a report written by the Joint International Commission for Theological Dialogue Between the Catholic Church and the Orthodox Church during its 7th plenary session at Balamand School of Theology in Lebanon stated:^[195][5] "Because of the way in which Catholics and Orthodox once again consider each other in their relationship to the mystery of the Church and discover each other once again as Sister Churches, this form of 'missionary apostolate' described above, and which has been called ′uniatism′, can no longer be accepted either as a method to be followed nor as a model of the unity our Churches are seeking". At the same time, the document inter alia stated:

In February 2016, Pope Francis and Patriarch Kirill of the Russian Orthodox Church (ROC), had a meeting in Cuba and signed a joint declaration that stated inter alia: "It is our hope that our meeting may also contribute to reconciliation wherever tensions exist between Greek Catholics and Orthodox. It is today clear that the past method of 'uniatism', understood as the union of one community to the other, separating it from its Church, is not the way to re-establish unity. Nonetheless, the ecclesial communities which emerged in these historical circumstances have the right to exist and to undertake all that is necessary to meet the spiritual needs of their faithful, while seeking to live in peace with their neighbours. Orthodox and Greek Catholics are in need of reconciliation and of mutually acceptable forms of co-existence."^{[196][197][198]} Meanwhile, in the interview published on the eve of the meeting in Cuba, Metropolitan Hilarion Alfeyev, the chairman of the Department of External Church Relations and a permanent member of the Holy Synod of the ROC, said that tensions between the Ukrainian Greek Catholic Church and the ROC's Ukrainian Orthodox Church had been recently heightened mainly due to the conflict in Ukraine.^[199] The declaration was sharply criticised by Sviatoslav Shevchuk, the Primate of the Ukrainian Greek Catholic Church, who said that his flock felt ″betrayed″ by the Vatican.^{[200][201][202]}

Inspired by the spirit of Vatican II that adopted the Unitatis Redintegratio decree on ecumenism in 1964 as well as the change of heart toward Ecumenism on the part of the Moscow Patriarchate that had occurred in 1961, the Vatican and 14 universally recognised autocephalous Orthodox Churches established the Joint International Commission for Theological Dialogue Between the Catholic Church and the Orthodox Church that first met in Rhodes in 1980 and is an ongoing endeavour.

On a number of occasions, Pope John Paul II recited the Nicene Creed with patriarchs of the Eastern Orthodox Church in Greek according to the original text.^[203] Both he and his successor, Pope Benedict XVI, have recited the Nicene Creed jointly with Patriarchs Demetrius I and Bartholomew I in Greek without the Filioque clause, "according to the usage of the Byzantine Churches".^[204][205] This accords with the Catholic Church's practice of including the clause when reciting the Creed in Latin,^[206] but not when reciting it in Greek.^[207]

In June 1995, Patriarch Bartholomew I, of Constantinople, visited Vatican City for the first time, and joined in the historic inter-religious day of prayer for peace at Assisi. John Paul II and Bartholomew I explicitly stated their mutual "desire to relegate the excommunications of the past to oblivion and to set out on the way to re-establishing full communion".^[208]

In May 1999, John Paul II was the first pope since the Great Schism to visit an Eastern Orthodox country: Romania. Upon greeting John Paul II, the Romanian Patriarch Teoctist stated: "The second millennium of Christian history began with a painful wounding of the unity of the Church; the end of this millennium has seen a real commitment to restoring Christian unity." John Paul II visited other heavily Orthodox areas such as Ukraine, despite lack of welcome at times, and he said that healing the divisions between Western and Eastern Christianity was one of his fondest wishes.

In June 2004, Bartholomew I's visit to Rome for the Feast of Saints Peter and Paul (29 June) afforded him the opportunity for another personal meeting with John Paul II, for conversations with the Pontifical Council for Promoting Christian Unity and for taking part in the celebration for the feast day in St. Peter's Basilica.

The Patriarch's partial participation in the Eucharistic liturgy at which the Pope presided followed the program of the past visits of Patriarch Dimitrios (1987) and Patriarch Bartholomew I himself: full participation in the Liturgy of the Word, joint proclamation by the Pope and by the Patriarch of the profession of faith according to the Nicene-Constantinopolitan Creed in Greek and as the conclusion, the final Blessing imparted by both the Pope and the Patriarch at the Altar of the Confessio.^[209] The Patriarch did not fully participate in the Liturgy of the Eucharist involving the consecration and distribution of the Eucharist itself.^[210][211]

Despite efforts on the part of Catholic Popes and Orthodox Patriarchs to heal the schism, only limited progress towards reconciliation has been made over the last half century. One stumbling block is the fact that the Orthodox and the Catholics have different perceptions of the nature of the divide. The official Catholic teaching is that the Orthodox are schismatic, meaning that there is nothing heretical about their theology, only their unwillingness to accept the supremacy of the Pope which is presented in Catholic teaching as chiefly an ecclesiological issue, not so much a theological one. The Orthodox object to the Catholic doctrines of Purgatory, Substitutionary atonement, the Immaculate Conception, and papal supremacy, among others, as heretical doctrines.^[212] With respect to Primacy of the Pope, the two churches agree that the Pope, as Bishop of Rome, has primacy although they continue to have different interpretations of what that primacy entails.

The Catholic Church's attitude was expressed by John Paul II in the image of the Church "breathing with her two lungs".^{[213][214][215]} He meant that there should be a combination of the more rational, juridical, organization-minded "Latin" temperament with the intuitive, mystical and contemplative spirit found in the East.^[216]

In the Orthodox view, the Bishop of Rome (i.e. the Pope) would have universal primacy in a reunited Christendom, as primus inter pares without power of jurisdiction.^[217]

The Eastern Orthodox insist that the primacy is largely one of honor, the Pope being "first among equals" primus inter pares. The Catholic Church, on the other hand, insists on the doctrine of Supremacy. It is widely understood that, if there is to be reconciliation, both sides will have to compromise on this doctrine. Although some commentators have proposed ways in which such compromise can be achieved, there is no official indication that such compromise is being contemplated.

In his book Principles of Catholic Theology, Pope Benedict XVI (then Cardinal Ratzinger) assessed the range of "possibilities that are open to Christian ecumenism." He characterized the "maximum demand" of the West as the recognition by the East of and submission to the "primacy of the bishop of Rome in the full scope of the definition of 1870..." The "maximum demand" of the East was described as a declaration by the West of the 1870 doctrine of papal primacy as erroneous along with the "removal of the Filioque from the Creed and including the Marian dogmas of the nineteenth and twentieth centuries." Ratzinger asserted that "(n)one of the maximum solutions offers any real hope of unity."^[218] Ratzinger wrote that, "Rome must not require more from the East than had been formulated and what was lived in the first millennium." He concluded that "Reunion could take place in this context if, on the one hand, the East would cease to oppose as heretical the developments that took place in the West in the second millennium and would accept the Catholic Church as legitimate and orthodox in the form she had acquired in the course of that development, while on the other hand, the West would recognize the Church of the East as orthodox in the form she has always had."^[219]

The declaration of Ravenna in 2007 re-asserted the belief that the bishop of Rome is indeed the protos, although future discussions are to be held on the concrete ecclesiological exercise of papal primacy.

Some scholars such as Jeffrey Finch assert that "the future of East–West rapprochement appears to be overcoming the modern polemics of neo-scholasticism and neo-Palamism".^[220]

These doctrinal issues center around the Orthodox perception that the Catholic theologians lack the actual experience of God called theoria and thereby fail to understand the importance of the heart as a noetic or intuitive faculty. It is what they consider to be the Catholic Church's reliance on pagan metaphysical philosophy and rational methods such as scholasticism rather than on intuitive experience of God (theoria) that causes Orthodox to consider the Catholic Church heretical. Other points of doctrinal difference include a difference regarding human nature as well as a difference regarding original sin, purgatory, and the nature of Hell.

One point of theological difference is embodied in the dispute regarding the inclusion of the Filioque in the Nicene Creed. In the view of the Catholic Church, what it calls the legitimate complementarity of the expressions "from the Father" and "from the Father and the Son" does not, provided it does not become rigid, affect the identity of faith in the reality of the same mystery confessed.^[221] The Orthodox, on the other hand, view inclusion of the phrase to be almost heretical (see also the Trinity section).

More importantly, the Orthodox see the Filioque as just the tip of the iceberg and really just a symptom of a much more deeply rooted problem of theology, one so deeply rooted that they consider it to be heretical and even, by some characterizations, an inability to "see God" and know God. This heresy is allegedly rooted in Frankish paganism, Arianism, Platonist and Aristotelian philosophy and Thomist rational and objective Scholasticism. In opposition to what they characterize as pagan, heretical and "godless" foundations, the Orthodox rely on an intuitive and mystical knowledge and vision of God (theoria) based on hesychasm and noesis. Catholics accept as valid the Eastern Orthodox intuitive and mystical understanding of God and consider it complementary to the rational Western reflection.^[216][222]

Most Orthodox Churches through economy do not require baptism in the Orthodox Church for one who has been previously baptized in the Catholic Church. Most Orthodox jurisdictions, based on that same principle of economy, allow a sacramental marriage between an Orthodox Christian and some non-Orthodox Christians. The Catholic Church allows its clergy to administer the sacraments of Penance, the Eucharist and Anointing of the Sick to members of the Eastern Orthodox Church, if these spontaneously ask for the sacraments and are properly disposed.^[223] It also allows Catholics who cannot approach a Catholic minister to receive these three sacraments from clergy of the Eastern Orthodox Church, whenever necessity requires or a genuine spiritual advantage commends it, and provided the danger of error or indifferentism is avoided.^[223] Catholic canon law allows marriage between a Catholic and an Orthodox.^[224] The Orthodox Church will only administer the sacraments to Christians who aren't Orthodox if there is an emergency.

The Code of Canons of the Eastern Churches authorizes the local Catholic bishop to permit a Catholic priest, of whatever rite, to bless the marriage of Orthodox faithful who being unable without great difficulty to approach a priest of their own Church, ask for this spontaneously.^[225] In exceptional circumstances Catholics may, in the absence of an authorized priest, marry before witnesses. If a priest who is not authorized for the celebration of the marriage is available, he should be called in, although the marriage is valid even without his presence.^[226] The Code of Canons of the Eastern Churches specifies that, in those exceptional circumstances, even a "non-Catholic" priest (and so not necessarily one belonging to an Eastern Church) may be called in.^[227]

The efforts of Orthodox patriarchs towards reconciliation with the Catholic Church has been strongly criticized by some elements of Eastern Orthodoxy, such as the Metropolitan of Kalavryta, Greece, in November 2008.^[228][229]

In 2010, Patriarch Bartholomew I issued an encyclical lauding the ongoing dialogue between the Orthodox Church and other Christian churches and criticizing those who are "unacceptably fanatical" in challenging such dialogue. The encyclical lamented that the dialogues between the two churches were being criticized in "an unacceptably fanatical way" by some who claim to be defenders of Orthodoxy despite the fact that these dialogues are being conducted "with the mutual agreement and participation of all local Orthodox Churches". The Patriarch warned that "such opponents raise themselves above episcopal synods and risk creating schisms". He further accused some critics of distorting reality to "deceive and arouse the faithful" and of depicting theological dialogue not as a pan-Orthodox effort, but an effort of the Ecumenical Patriarchate alone. As an example, he pointed to "false rumors that union between the Roman Catholic and Orthodox Churches is imminent" claiming that the disseminators of such rumors were fully aware that "the differences discussed in these theological dialogues remain numerous and require lengthy debate". The Patriarch re-emphasized that "union is not decided by theological commissions but by Church Synods".^[230]

Jaroslav Pelikan emphasizes that "while the East–West schism stemmed largely from political and ecclesiastical discord, this discord also reflected basic theological differences". Pelikan further argues that the antagonists in the 11th century inappropriately exaggerated their theological differences whereas modern historians tend to minimize them. Pelikan asserts that the documents from that era evidence the "depths of intellectual alienation that had developed between the two sections of Christendom." While the two sides were technically more guilty of schism than heresy, they often charged each other with allegations of heresy. Pelikan describes much of the dispute as dealing with "regional differences in usages and customs" some of which were adiaphorus (i.e. neither right nor wrong). However, he goes on to say that while it was easy in principle to accept the existence of adiaphora, it was difficult in actual practice to distinguish customs which were innocuously adiaphoric from those that had doctrinal implications.^[231]

Philip Sherrard, an Orthodox theologian asserts that the underlying cause of the East–West schism was and continues to be "the clash of these two fundamentally irreconcilable ecclesiologies." Roger Haight characterizes the question of episcopal authority in the Church as "acute" with the "relative standings of Rome and Constantinople a recurrent source of tension." Haight characterizes the difference in ecclesiologies as "the contrast between a pope with universal jurisdiction and a combination of patriarchal superstructure with an episcopal and synodal communion ecclesiology analogous to that found in Cyprian."^[24]

However, Nicholas Afansiev has criticized both the Catholic and Orthodox churches for "subscribing to the universal ecclesiology of St. Cyprian of Carthage according to which only one true and universal church can exist."^[232]

There are several different ecclesiologies: "communion ecclesiology", "eucharistic ecclesiology", "baptismal ecclesiology", "trinitarian ecclesiology", "kerygmatic theology".^[233] Other ecclesiologies are the "hierarchical-institutional" and the "organic-mystical",^[234] and the "congregationalist".^[235]

The Eastern Churches maintained the idea that every local city-church with its bishop, presbyters, deacons and people celebrating the Eucharist constituted the whole Church. In this view called Eucharistic ecclesiology (or more recently holographic ecclesiology), every bishop is Saint Peter's successor in his church ("the Church") and the churches form what Eusebius called a common union of churches. This implied that all bishops were ontologically equal, although functionally particular bishops could be granted special privileges by other bishops and serve as metropolitans, archbishops or patriarchs. Within the Roman Empire, from the time of Constantine to the final extinction of the empire in 1453, universal ecclesiology, rather than eucharistic, "became the operative principle".^[236][237] The view prevailed that, "when the Roman Empire became Christian the perfect world order willed by God had been achieved: one universal empire was sovereign, and coterminous with it was the one universal church".^[238] Early on, the ecclesiology of the Roman Church was universal in nature, with the idea that the Church was a worldwide organism with a divinely (not functionally) appointed center: the Church/Bishop of Rome. These two views are still present in modern Eastern Orthodoxy and Catholicism and can be seen as foundational causes for the schisms and Great Schism between East and West.

"The Orthodox Church does not accept the doctrine of Papal authority set forth in the Vatican Council of 1870, and taught today in the Catholic Church."^[239] The Orthodox Church has always maintained the original position of collegiality of the bishops resulting in the structure of the church being closer to a confederacy.^[240] The Orthodox have synods where the highest authorities in each Church community are brought together, but, unlike the Catholic Church, no central individual or figure has the absolute and infallible last word on church doctrine. In practice, this has sometimes led to divisions among Greek, Russian, Bulgarian and Ukrainian Orthodox churches, as no central authority can serve as a rallying point for various internal disputes.

Early on, the ecclesiology of the Roman Church was universal in nature, with the idea that the Church was a worldwide organism with a divinely (not functionally) appointed center: the Church/Bishop of Rome. Vatican II re-asserted the importance of collegiality to a degree that appears satisfying to most if not all ecclesial parties. Starting from the second half of the 20th century, eucharistic ecclesiology is upheld by Catholic theologians. Henri de Lubac wrote: "The Church, like the Eucharist, is a mystery of unity – the same mystery, and one with inexhaustible riches. Both are the body of Christ – the same body."^[241] Joseph Ratzinger called eucharistic ecclesiology "the real core of Vatican II's teaching on the cross".^[234] According to Ratzinger, the one church of God exists in no other way than in the various individual local congregations.^[242] In these the Eucharist is celebrated in union with the Church everywhere.^[243] Eucharistic ecclesiology led Vatican II to "affirm the theological significance of the local church. If each celebration of the Eucharist is a matter not only of Christ's sacramental presence on the altar, but also of his ecclesial presence in the gathered community, then each eucharistic local church must be more than a subset of the universal church; it must be the body of Christ 'in that place'."^[244]

The ecclesiological dimension of the East–West schism revolves around the authority of bishops within their dioceses^[245] and the lines of authority between bishops of different dioceses. It is common for Catholics to insist on the primacy of Roman and papal authority based on patristic writings and conciliar documents.^[246]

The Catholic Church's current official teachings about papal privilege and power that are unacceptable to the Eastern Orthodox churches are the dogma of the pope's infallibility when speaking officially "from the chair of Peter (ex cathedra Petri)" on matters of faith and morals to be held by the whole Church, so that such definitions are irreformable "of themselves, and not by the consent of the Church" (ex sese et non-ex consensu ecclesiae)^[247] and have a binding character for all (Catholic) Christians in the world; the pope's direct episcopal jurisdiction over all (Catholic) Christians in the world; the pope's authority to appoint (and so also to depose) the bishops of all (Catholic) Christian churches except in the territory of a patriarchate;^[248] and the affirmation that the legitimacy and authority of all (Catholic) Christian bishops in the world derive from their union with the Roman see and its bishop, the Supreme Pontiff, the unique Successor of Peter and Vicar of Christ on earth.

Principal among the ecclesiastical issues that separate the two churches is the meaning of papal primacy within any future unified church. The Orthodox insist that it should be a "primacy of honor", as in the ancient church, and not a "primacy of authority",^[249] whereas the Catholics see the pontiff's role as requiring for its exercise power and authority the exact form of which is open to discussion with other Christians.^[250]

According to Orthodox belief, the test of catholicity is adherence to the authority of Scripture and then by the Holy Tradition of the church. It is not defined by adherence to any particular See. It is the position of the Orthodox Church that it has never accepted the pope as de jure leader of the entire church. All bishops are equal 'as Peter' therefore every church under every bishop (consecrated in apostolic succession) is fully complete (the original meaning of catholic).

Referring to Ignatius of Antioch^[251] Carlton says

The church is in the image of the Trinity^[253] and reflects the reality of the incarnation.

Any changes to the understanding of the church would reflect a change in the understanding of the Trinity.

From the perspective of the Catholic Church, the ecclesiological issues are the central issue which is why they characterize the split between the two churches as a schism. In their view, the Eastern Orthodox are very close to them in theology and the Catholic Church does not consider the Orthodox beliefs to be heretical. However, from the perspective of Orthodox theologians, there are theological issues that run much deeper than just the theology around the primacy and/or supremacy of the Pope. In fact, unlike the Catholics, who do not generally consider the Orthodox heretical and speak instead about the Eastern "schism",^[155] some prominent Orthodox theologians do consider the Catholic Church to be heretical on fundamental doctrinal issues of theology, such as the Filioque. These issues have a long history as can be seen in the 11th-century works of Orthodox theologian and Saint Nikitas Stithatos.

In the Catholic Church too, some writers can be found who speak pejoratively of the Eastern Orthodox Church and its theology, but these writers are marginal.^[255] The official view of the Catholic Church is that expressed in the decree Unitatis redintegratio of Vatican II:

Although the Western churches do not consider the Eastern and Western understanding of the Trinity to be radically different, Eastern theologians such as John S. Romanides and Michael Pomazansky argue that the Filioque clause is symptomatic of a fatal flaw in the Western understanding, which they attribute to the influence of Augustine and, by extension, to that of Thomas Aquinas.^{[257][258][259][260][261]}

Filioque, Latin for "and (from) the Son", was added in Western Christianity to the Latin text of the Nicene-Constantinopolitan Creed, which also varies from the original Greek text in having the additional phrase Deum de Deo (God from God)^[262][263] and in using the singular "I believe" (Latin, Credo, Greek Πιστεύω) instead of the original "We believe" (Greek Πιστεύομεν),^[263] which Oriental Orthodoxy preserves.^[264] The Assyrian Church of the East, which is in communion neither with the Eastern Orthodox Church nor with Oriental Orthodoxy also uses "We believe".^[265] Filioque states that the Holy Spirit proceeds from the Son as well as from the Father, a doctrine accepted by the Catholic Church,^[266] by Anglicanism^[267] and by Protestant churches in general.^[268] Christians of these groups generally include it when reciting the Nicene Creed. Nonetheless, these groups recognize that Filioque is not part of the original text established at the First Council of Constantinople in 381^[269] and they do not demand that others too should use it when saying the Creed.^[270] Indeed, the Catholic Church does not add the phrase corresponding to Filioque (καὶ τοῦ Υἱοῦ) to the Greek text of the Creed, even in the liturgy for Latin Rite Catholics.^[271]

At the 879–880 Council of Constantinople the Eastern Orthodox Church anathematized the "Filioque" phrase, "as a novelty and augmentation of the Creed", and in their 1848 encyclical the Eastern Patriarchs spoke of it as a heresy.^[272] It was qualified as such by some of the Eastern Orthodox Church's saints, including Photios I of Constantinople, Mark of Ephesus, Gregory Palamas, who have been called the Three Pillars of Orthodoxy.

The Eastern church believes by the Western church inserting the Filioque unilaterally (without consulting or holding council with the East) into the Creed that the Western church broke communion with the East.^[121]

Orthodox theologians such as Vladimir Lossky criticize the focus of Western theology of God in 'God in uncreated essence' as misguided, which he alleges is a modalistic and therefore a speculative expression of God that is indicative of the Sabellian heresy.^[273] Orthodox theologian Michael Pomazansky argues that, in order for the Holy Spirit to proceed from the Father and the Son in the Creed, there would have to be two sources in the deity (double procession), whereas in the one God there can only be one source of divinity, which is the Father hypostasis of the Trinity, not God's essence per se.^[274] In contrast, Bishop Kallistos Ware suggests that the problem is more in the area of semantics than of basic doctrinal differences.^[275]

Lossky, a noted modern Eastern Orthodox theologian, argues the difference in East and West is due to the Catholic Church's use of pagan metaphysical philosophy (and scholasticism) rather than actual experience of God called theoria, to validate the theological dogmas of Catholic Christianity. For this reason, Lossky argues that Eastern Orthodox and Catholics have become "different men".^[276] Other Eastern Orthodox theologians such as Romanides^[277] and Metropolitan Hierotheos of Nafpaktos have made similar pronouncements.^[278] According to the Orthodox teachings, theoria can be achieved through ascetic practices like hesychasm (see St John Climacus), which was condemned as a heresy by Barlaam of Seminara.

Orthodox theologians charge that, in contrast to Orthodox theology, western theology is based on philosophical discourse which reduces humanity and nature to cold mechanical concepts.^[279][280] Orthodox theologians argue that the mind (reason, rationality) is the focus of Western theology, whereas in Eastern theology, the mind must be put in the heart, so they are united into what is called nous, this unity as heart is the focus of Eastern Orthodox Christianity^[281] involving the unceasing Prayer of the heart.^[282]

In Orthodox theology, in the Eastern ascetic traditions one of the goals of ascetic practice is to obtain sobriety of consciousness, awakeness (nepsis). For humankind this is reached in the healing of whole person called the soul, heart. When a person's heart is reconciled with their mind, this is referred to as a healing of the nous or the "eye, focus of the heart or soul".^[283][284] Part of this process is the healing and or reconciliation of humankind's reason being called logos or dianoia with the heart, soul.^[285] While mankind's spirit and body are energies vivified by the soul, Orthodoxy teaches man's sin, suffering, sorrow is caused by his heart and mind being a duality and in conflict.^[286] According to Orthodox theology, lack of noetic understanding (sickness) can be neither circumvented nor satisfied by rational or discursive thought (i.e. systematization),^[283] and denying the needs of the human heart (a more Western expression would be the needs of the soul) causes various negative or destructive manifestations such as addiction, atheism and evil thoughts etc.^[287][288] A cleaned, healed or restored Nous creates the condition of sobriety or nepsis of the mind.

Orthodox theologians assert that the theological division of East and West culminated into a direct theological conflict known as the Hesychasm controversy during several councils at Constantinople New Rome, between the years 1341–1351. They argue that this controversy highlighted the sharp contrast between what is embraced by the Catholic Church as proper (or orthodox) theological dogma and how theology is validated and what is considered valid theology by the Eastern Orthodox. The essence of the disagreement is that in the East a person cannot be a genuine true theologian, or teach knowledge of God, without having experienced God, as is defined as the vision of God (theoria). At the heart of the issue was the teaching of the Essence-Energies distinctions (which states that while creation can never know God's uncreated essence, it can know his uncreated energies) by Gregory Palamas.

The Eastern Orthodox do not accept Augustine's teaching of original sin. His interpretation of ancestral sin is rejected in the East as well. Nor is Augustine's teaching accepted in its totality in the West.^[289] The Catholic Church rejects traducianism and affirms creationism. Its teaching on original sin is largely based on but not identical with that of Augustine, and is opposed to the interpretation of Augustine advanced by Martin Luther and John Calvin. Its teaching departs from Augustine's ideas in some respects.^[289][290] The Eastern Church makes no use at all of Augustine. Another Orthodox view is expressed by Christos Yannaras, who described Augustine as "the fount of every distortion and alteration in the Church's truth in the West".^[291]

What the Eastern Orthodox accepts is that ancestral sin corrupted their existence (their bodies and environment) that each person is born into and thus we are born into a corrupted existence (by the ancestral sin of Adam and Eve)^[292] and that "original sin is hereditary. It did not remain only Adam and Eve's. As life passes from them to all of their descendants, so does original sin. All of us participate in original sin because we are all descended from the same forefather, Adam."^[293] And the teaching of the Eastern Orthodox Church is that, as a result of Adam's sin, "hereditary sin flowed to his posterity; so that everyone who is born after the flesh bears this burden, and experiences the fruits of it in this present world."^[294]

Similarly, what the Catholic Church holds is that the sin of Adam that we inherit, and for the remission of which even babies who have no personal sin are baptized,^[295] is called "sin" only in an analogical sense, since it is not an act committed like the personal sin of Adam and Eve, but a fallen state contracted by the transmission of a human nature deprived of original holiness and justice.^[296]

Both East and West^[296] hold that each person is not called to atone for the actual sin committed by Adam and Eve.

According to the Western Church, "original sin does not have the character of a personal fault in any of Adam's descendants",^[296] and the Eastern Church teaches that "by these fruits and this burden we do not understand [actual] sin".^[294] The Orthodox and the Catholics^[297] believe that people inherit only the spiritual sickness (in which all suffer and sin) of Adam and Eve, caused by their ancestral sin (what has flowed to them), a sickness leaving them weakened in their powers, subject to ignorance, suffering and the domination of death, and inclined to sin.^[297]

The Catholic doctrine of the Immaculate Conception, which claims that God protected the Virgin Mary from original sin through no merit of her own,^[298][299] was dogmatically defined by Pope Pius IX in 1854. Instead, Orthodox theology proclaims that Mary was chosen to bear Christ, having first found favor of God by her purity and obedience.^{[300][301][302][303][304][305]}

Another point of theological contention between the western and eastern churches is the doctrine of purgatory (as it was shown at the Second Council of Lyons and the Council of Ferrara–Florence).^[306] It was developed in time in western theology, according to which, "all who die in God's grace and friendship, but still imperfectly purified, are indeed assured of their eternal salvation; but after death they undergo purification, so as to achieve the holiness necessary to enter the joy of heaven."^[307] However, some eastern theologians, while agreeing that there is beyond death a state in which believers continue to be perfected and led to full divinization, consider that it is a state not of punishment but of growth;^[308] hold that suffering cannot purify sin, since they have a different view of sin and consider suffering as a result of a spiritual sickness.^[309] Western theology usually considers sin not only as a sickness that weakens and impedes, but also as something that merits punishment.^[310]

The Eastern Orthodox Church holds that "there is a state beyond death where believers continue to be perfected and led to full divinization".^[308] Although some Orthodox have described this intermediate state as purgatory, others distinguish it from aspects associated with it in the West: at the Council of Ferrara–Florence, the Orthodox Bishop Mark of Ephesus argued that there are in it no purifying fires.^[311]

The traditional Orthodox teaching is that "those who reject Christ will face punishment. According to the Confession of Dositheus, persons go immediately to joy in Christ or to the torments of punishment".^[308]

In Orthodox doctrine there is no place without God. In eternity there is no hiding from God. In Catholic theology, God is present everywhere not only by his power but in himself.^[312] Hell is a state of self-selected separation from God.

Eastern theology considers the desire to sin to be the result of a spiritual sickness (caused by Adam and Eve's pride), which needs to be cured.^[313] One such theologian gives his interpretation of Western theology as follows: "According to the holy Fathers of the Church, there is not an uncreated Paradise and a created Hell, as the Franco–Latin tradition teaches".^[314] The eastern Church believes that hell or eternal damnation and heaven exist and are the same place, which is being with God, and that the very same divine love (God's uncreated energies) which is a source of bliss and consolation for the righteous (because they love God, His love is heaven for them) is also a source of torment (or a "Lake of Fire") for sinners (because they don't love God, they will feel His love this way).^{[315][316][317][318]} The Western Church speaks of heaven^[319] and hell^[320] as states of existence rather than as places, while in Eastern Orthodoxy there is no hell per se, there is damnation or punishment in eternity for the rejection of God's grace.