Theological differences between the Catholic Church and the Eastern Orthodox Church

The Catholic Church and the Eastern Orthodox Church have been in a state of official schism from one another since the East–West Schism of 1054. This schism was caused by historical and linguistic differences, and the ensuing theological differences between the Western and Eastern churches.
The main theological differences with the Catholic Church are the papal primacy and the filioque clause. In spirituality, the tenability of neo-Palamism's essence-energy distinction and of the experiential vision of God as attained in theoria and theosis are actively debated.
Although the 21st century saw a growth of anti-Western sentiments with the rise of neo-Palamism, "the future of East–West rapprochement appears to be overcoming the modern polemics of neo-scholasticism and neo-Palamism". Since the Second Vatican Council, the Catholic Church has generally taken the approach that the schism is primarily ecclesiological in nature, that the doctrinal teachings of the Eastern Orthodox churches are generally sound, and that "the vision of the full communion to be sought is that of unity in legitimate diversity" as before the division.

Areas of doctrinal agreement

Both churches accept the decisions of the first seven Ecumenical Councils of the undivided Church. These are:
There is therefore doctrinal agreement on:
Both churches reject many Protestant doctrines; some important examples are the teachings of salvation through faith alone and sola scriptura.

East–West Schism

Papal primacy

Papal primacy, also known as the "primacy of the Bishop of Rome," is an ecclesiastical doctrine concerning the respect and authority that is due to the pope from other bishops and their episcopal sees.
In the Eastern Orthodox Church, some understand the primacy of the Bishop of Rome to be merely one of greater honour, regarding him as primus inter pares, without effective power over other churches. A prominent 20th-century Eastern Orthodox Christian theologian, Fr. Alexander Schmemann, envisioned a primacy that sums up rather than rules over: "Primacy is power, but as power it is not different from the power of a bishop in each church. It is not a higher power but indeed the same power, only expressed, manifested, and realized by one."
The Catholic Church attributes to the primacy of the Pope "full, supreme, and universal power over the whole Church, a power which he can always exercise unhindered," with a power that it attributes also to the entire body of the bishops united with the pope. The power that it attributes to the pope's primatial authority has limitations that are official, legal, dogmatic, and practical.
In the Ravenna Document, issued in 2007, representatives of the Eastern Orthodox Church and the Catholic Church jointly stated that both East and West accept the fact of the Bishop of Rome's primacy at the universal level, but that differences of understanding exist about how the primacy is to be exercised and about its scriptural and theological foundations.

''Filioque''

Differences over this doctrine and the question of papal primacy have been and remain primary causes of schism between the Eastern Orthodox and Western churches. The term has been an ongoing source of conflict between Eastern Christianity and Western Christianity, contributing, in major part, to the East–West Schism of 1054 and proving to be an obstacle to attempts to reunify the two sides.

The ''Filioque'' clause

Filioque is a Latin term added to the Niceno-Constantinopolitan Creed, which is absent in the original Greek version. The Latin term Filioque is translated into the English clause "and the Son" in that creed:
or in Latin:

Inclusion and rejection

The Filioque was accepted by the popes only in 1014 and is rejected by the Eastern Orthodox Church, Oriental Orthodox Churches and Church of the East. first appearing in the 6th century.

Consequences

Whether that term Filioque is included, as well as how it is translated and understood, can have important implications for how one understands the central Christian doctrine of the Holy Trinity. For some, the term implies a serious underestimation of the Father's role in the Trinity; for others, denial of what it expresses implies a serious underestimation of the role of the Son in the Trinity. Over time, the term became a symbol of conflict between Eastern Christianity and Western Christianity, although there have been attempts at resolving the conflict. Among the early attempts at harmonization are the works of Maximus the Confessor, who notably was canonised independently by both the Eastern and Western churches.

Possible linguistic resolution

In 1995, the Pontifical Council for Promoting Christian Unity pointed out that the Filioque conundrum may be a problem of language, rather than a problem of theology. The word ἐκπορεύεσθαι in Greek indicates a primary cause or an ultimate cause; while the Latin word procedere indicates a procession but not from an ultimate cause. The Latin version may be more accurately retranslated into Greek as προϊέναι, rather than ἐκπορεύεσθαι. Metropolitan John Zizioulas declared that PCPCU position shows positive signs of reconciliation for the Filioque issue between the Eastern and Western churches.

The sacraments

With regard to the Eucharist, both the Orthodox and Catholic Churches believe in the real presence but differ on transubstantiation. The Orthodox Church holds that it is not the words of institution that change the substance into the Body and Blood, as is done in the Western liturgical rites, but instead, the epiclesis, which was not in the Roman Rite until 1969. Communion bread also varies between the Catholic and Orthodox Churches, with the Orthodox Church using leavened bread while Catholic Church uses unleavened bread.
Regarding the sacrament of holy orders, in the Orthodox married men can be ordained but, if they become widowed, they cannot remarry. Bishops are chosen from the monks. In this, the Orthodox Church is closer to Catholics of oriental rites. In the Catholic Church, however, with the exception of the Eastern liturgical rites, priests maintain celibacy.
The age of confirmation and holy communion also varies between Catholics and Orthodox; Orthodox infants receive chrismation and holy communion immediately after baptism, while Catholic children receive their first communion and confirmation from the age of 7.

Neo-Palamism: theoria and hesychasm

Neo-Palamism

The 20th century saw the rise of neo-Palamism, c.q. "Neo-Orthodox Movement," in the Eastern Orthodox Churches. According to this point of view, which arose in defense of the Palamite distinction between essence and energia, Western theology is dominated by rational philosophy, while Orthodox theology is based on the experiential vision of God and the highest truth. According to neo-Palamism, this is a main division between East and West.
Neo-Palamism has its roots in the Hesychast controversy or Palamite controversy,
in which Gregory Palamas provided a theological justification for the centuries-old Orthodox practice of hesychasm. The hesychast controversy lead to a further distinction between East and West, with Palamite doctrine being accepted as orthodox in the Fifth Council of Constantinople, giving a prominent place to the contemplative practice and theology in the Eastern Orthodox Church. The publication in 1782 of the Philokalia, which lead to a revival of hesychasm, was accepted in particular by the Slav Orthodox churches. Together with the importance attached to it in the 20th century by the Paris school of Orthodox theology, it has "led to hesychasm's becoming definitive for modern Orthodox theology as never before," with its Palamite Essence–energies distinction.

Rational and mystical theology

According to these modern Eastern Orthodox theologians, Western theology depends too much on kataphatic theology. According to Steenberg, Eastern theologians assert that Christianity in essence is apodictic truth, in contrast to the dialectic, dianoia, or rationalised knowledge which is the arrived at truth by way of philosophical speculation.
While Thomas Aquinas argued that kataphatic and apophatic theology need to balance each other, Vladimir Lossky argued, based on his reading of Dionysius the Areopagite and Maximus the Confessor, that positive theology is always inferior to negative theology. According to Lossky mysticism, c.q. gnosiology, is the expression of dogmatic theology par excellence, while positive theology is a step along the way to the superior knowledge attained by negation. According to Lossky, the difference in East and West is due to the Catholic Church's use of pagan metaphysical philosophy, and its outgrowth, scholasticism, rather than the mystical, actual experience of God called theoria, to validate the theological dogmas of Catholic Christianity. Lossky argues that therefore the Eastern Orthodox and Catholics have become "different men," stating that "Revelation sets an abyss between the truth which it declares and the truths which can be discovered by philosophical speculation."
Lossky had a strong influence on 20th century Eastern Orthodox theology, and influenced John Romanides, himself also an influential theologian on his own. Romanides saw a strong dichotomy between Eastern Orthodox and Western views, arguing that the influence of the Franks, and Western acceptance of Augustine's theology, is the starting point of Western rational theology, and the dichotomy between East and West.
This same sentiment was also expressed by the early Slavophile movements in the works of Ivan Kireevsky and Aleksey Khomyakov. The Slavophiles sought reconciliation with all various forms of Christianity, as can be seen in the works of its most famous proponent Vladimir Solovyov.