The list below highlights some (but by no means all) of the doctrinal, liturgical, and ecclesiological differences that exist between the Roman Church, on the one hand, and the Eastern Orthodox and Eastern Catholic Churches, on the other. I have — for the sake of clarity — broken the differences down into three topic sections:

[A] Theological Differences

(01) East and West view the Trinity somewhat differently. The West tends to follow Thomas Aquinas and the Augustinian tradition, which looks upon the persons (hypostaseis) of the Trinity as relations of opposition within the divine essence (ousia), and which holds that it is the unity of the divine essence (ousia) itself that establishes the fact that there is only one God. While the East holds — in line with the teaching of St. Athanasios and the Cappadocian Fathers — that there can be no opposition in God and that the three divine persons (hypostaseis) are instead really distinct from each other, not because of their relations per se, but because each person has a unique mode of existence (tropos hyparxeos). Thus, the person (hypostasis) of the Father is distinct from the person (hypostasis) of the Son and the person (hypostasis) of the Spirit, because the Father is the unoriginate cause (aitia) of divinity; while the Son is eternally generated by the Father alone, and the Holy Spirit is eternally processed from the Father alone, as the sole personal cause (aitia) of divinity. In other words, the person (hypostasis) of the Father is unbegotten, and the person (hypostasis) of the Son is begotten by the Father, and the person (hypostasis) of the Holy Spirit is spirated by the Father through procession (ekporeusis). Consequently, in the theology of the East there is only one God because there is only one Father from whom all Godhead eternally originates.

(02) In the West, God is held to be pure act (actus purus), and as such there are no real distinctions within the Godhead, because even the three divine persons (hypostaseis) are only distinct in relation to each other, and not to the divine essence (ousia). Thus — in Western theology — essence (ousia) and person (hypostasis) are identical in God [see Summa Theologica, Prima Pars, Q. 39, art. 1]; while — in Eastern theology — essence (ousia) and person (hypostasis) are really distinct from each other [See St. Basil, "Letter 38"]. Moreover, in addition to the real distinction between essence (ousia) and person (hypostasis) in Eastern triadology, there is also a distinction made between essence (ousia) and energy (energeia) within God, with the divine energy being God's uncreated glory, which flows out to mankind as a gift of His life and grace [see St. Basil, "Letter 234"].

(03) Along with these theological distinctions (i.e., essence, person, and energy) it is held that the divine essence (ousia) itself is completely unknowable, because God, in His essence (ousia), is truly beyond essence (hyperousios) and beyond God (hypertheos). As a consequence, God does not reveal Himself in His essence (ousia); instead, He reveals Himself tri-personally through His uncreated energies (energeiai).

(04) From what has been said in the points above, it becomes clear that the West and the East understand the divine simplicity differently. The West holds that in God there are no real distinctions between, what it calls, His attributes and His essence (ousia), thus all of the divine attributes are identical with the divine essence. While in the East, divine simplicity is understood as the co-inherence or interpenetration (perichoresis) of the inexplicable divine essence in the multiplicity of God's uncreated energies; and so, each energy is distinct from every other energy (e.g., the divine will is distinct from the divine love, which is distinct from truth, which is distinct from mercy, which is distinct from divine justice, etc.), but God is present as a whole in each one of the distinct energies [see St. Basil the Great's, "Letter 234" and "Letter 189"]. This means that the one divinity is indivisibly divided among the personalized (enhypostatic) energies of the three divine persons (hypostaseis). Now the term enhypostatic is used in Orthodox theology as a contrast to the terms authypostatic and anhypostatic. That which is enhypostatic is not self-subsisting (i.e., authypostatic), nor is it merely transitory or illusory (i.e., anhypostatic), but is instead a real quality inhering in a person (hypostasis). Taking into account what has been said up to this point, a note of clarification is now necessary because although the uncreated energies correspond in some sense to what the West calls attributes, to identify these two terms (attributes and energies) can lead to theological confusion. In the West the divine attributes are normally held to be distinct only in a noetic sense, that is, they are held to be distinct merely mentally in the mind of the onlooker; and that is why the East avoids the use of the term "attributes" when referring to God's uncreated energies, because that would undermine the real distinction (pragmatika diakrisis) that exists between essence (ousia) and energy (energeia) in God, reducing it to an epistemic distinction. Moreover, to reduce the distinction between the divine essence and the uncreated divine energies to something that is merely epistemic leads to major theological problems within the Eastern Orthodox and Eastern Catholic tradition in connection with the doctrine of divinization (theosis).

(05) As I indicated above, the East makes a further real distinction (pragmatika diakrisis) — without a real division (pragmatike diaresis) — in the Godhead between the divine essence (ousia) and the uncreated divine energies (energeiai). The divine essence (ousia) is completely incommunicable and transcendent, and as such it is beyond essence (hyperousios); consequently it cannot be known, not now, nor even in the eschaton. God is revealed only in His uncreated energies, which flow out from the three divine persons (hypostaseis) as a gift to man (i.e., as grace). Moreover, it is only by man's participation in the divine energies that he can truly possess an experiential knowledge of God, an experience that can be understood in two ways: first, at the level of nature by the sustaining of man's created existence; and second, at the level of the supernatural through the elevation of man's being into the life and glory of the Triune God, which is primarily accomplished through the divine liturgy.

(06) The West, at least since the time of the Scholastics, has taught that grace is a created reality; while the East — on the other hand — holds that grace is uncreated. In the East grace — as I indicated above — is divine energy (energeia), which means that grace is God Himself as He exists for us, that is, as He exists outside of His incommunicable essence (ousia), and so there is no concept of "created grace" in the Eastern Orthodox and Eastern Catholic tradition. For the Eastern Christian the concept of "created grace" ultimately involves the reduction of the gift of theosis to a causal relationship in which — for lack of a better word — a "created thing" stands between the uncreated God and man; while it (i.e., this created light or habitus) somehow "deifies" the human person with a "created divinity," and this idea really is just another form of the errors espoused by the Arian and Pneumatomachian heretics of the 4th century AD.

(07) As a consequence of its teaching on grace, the East holds that divinization (theosis) is brought about by an ontological participation in God's uncreated energies, and that through the divine energies man truly participates in the divine life and glory. The uncreated energies are God as He exists outside of His incomprehensible essence (ousia), and so it must be said that the divine energies — as the things around God (ta peri Theon) — are truly distinct from the divine essence, but without being separated from it. St. Gregory Palamas says the following about the process of theosis in his "Third Letter to Akindynos":

(08) The Eastern Orthodox and Eastern Catholic understanding of predestination also differs from that of the West. The East holds that all men at the level of nature are predestined to redemption through the incarnation of the Son of God. In other words, through the incarnation of the eternal Logos all of human nature has been freed from corruption and the dissolution into non-existence brought about by the ancestral sin of Adam, and has been given the gift of redemption to everlasting existence. But salvation, on the other hand, concerns the integration of the human person (hypostasis) with his natural virtues through the power of God's uncreated energies and the activity of his own created free will. Salvation requires that a man enact his will through grace in doing good and avoiding evil. If a man lives a good life through the power of his will restored by grace, he may enter into the vision of God, but if he fails to integrate his natural virtues into his person (hypostasis) by living a life of sin and vice, he damns himself. Thus, in Eastern theology predestination is the universal redemption of all men, and of the whole of creation itself, from corruption and non-existence; while salvation involves the integration of man's natural virtues with his personal (hypostatic) existence through the power of God's uncreated energies and his own free will.

(09) In the doctrine of the Eastern Church Fathers there are three forms of union within the Godhead: the first form of union is that experienced by the persons of the Holy Trinity, who are distinct from each other personally (hypostatically), while being perfectly one in the unity of the divine essence (ousia); the second form of union is what is called the hypostatic union, and this union is experienced only by the second person of the Holy Trinity (i.e., the Son of God made man), who united human nature to His divine hypostasis and became incarnate from the Virgin Theotokos; and finally, the third form of union within the Godhead is experienced by the saints, that is, by those who have emulated Christ in their earthly lives through the power of God's deifying grace, but who will remain for all eternity distinct from God both essentially and hypostatically. This third form of union with the Triune God is achieved by participation in the uncreated divine energies (i.e., the actualized powers of the three divine persons), which make a man into a perfect likeness (homoiosis) of God. So to summarize the foregoing information, the three types of divine unity are: (1) essential unity, (2) hypostatic unity, and (3) energetic unity.

[B] Liturgical Differences

(10) Westerners and Easterners make the sign of the cross somewhat differently, with Easterners making the sign from forehead to the center of the torso, and then from the right shoulder to the left shoulder (or over the heart). The West began making the sign of the cross ending on the right shoulder beginning at some point around the 12th to 13th century.

(11) The use of the filioque (which means "and from the Son") in the final section of the Niceno-Constantinopolitan creed in connection with the procession of the Holy Spirit is not accepted as legitimate by the Eastern Orthodox, but is accepted by Eastern Catholics as a Western liturgical innovation. The Niceno-Constantinopolitan creed as it was originally written did not include the filioque, but the West added the filioque to the creed beginning in Spain around the 7th century, with the filioque finally being added at Rome itself at some point during the early part of the 11th century [see the Addendum at the bottom of this outline for more information on why Eastern Christians do not recite the creed with the filioque].

(12) In the Eastern Churches married men can be ordained to both the diaconate and the priesthood; but, like the Latin Church, only celibate men can be consecrated as bishops.

(13) In Byzantine sacramental theology the priest (and not the couple) is the minister of the sacrament of matrimony, and so his blessing is necessary for the validity of the sacrament, which is called "Crowning" in the East. This also means that a deacon cannot officiate at an Eastern Orthodox or Eastern Catholic wedding.

(14) In Eastern theology the bread and wine of the Eucharist are held to be consecrated into the body and blood of Christ by the whole anaphora, and specifically by the prayer of epiclesis (i.e., the calling down of the Spirit upon the gifts), and not by the "words of institution" as in the West.

(15) In the celebration of the Eucharist the Eastern Churches use leavened bread, not unleavened bread, and as Fr. Jungmann explained in his magnum opus on the Roman liturgy this difference arose in the 9th century when the Roman Church broke with the original practice of using leavened bread [see Fr. Joseph Jungmann, Mass of the Roman Rite, 2:33-34; see also Fr. Adrian Fortescue, The Mass: A Study of the Roman Liturgy, pages 300-303; see also Fr. Johannes H. Emminghaus, The Eucharist: Essence, Form, Celebration, pages 70 and 162].

(16) The Eastern Churches, unlike the Latin Church and the Protestant Churches, use the Greek translation of the Old Testament commonly referred to as the Septuagint (LXX), and because of this difference the Eastern Orthodox and Eastern Catholic Churches have a somewhat larger canon of scripture than the Latin Church (e.g., Eastern Churches — Orthodox and Catholic — chant the "Prayer of Manasseh" as scripture during Great Compline).

(17) In the Eastern Churches — both Orthodox and Catholic — icons are always two dimensional images written according to specific aesthetic canons (rules) often referred to as "reverse perspective," and so one will rarely if ever see statuary (or even naturalistic paintings) in an Eastern Orthodox or Eastern Catholic Church (except those that have perhaps suffered a degree of Latinization). 

(18) Icons are also believed to contain divine energy, which means that they are a mystery (i.e., a sacrament) that bestows grace upon those who venerate them. Icons, because they are filled with God's uncreated energy, manifest the person or event depicted in them, and are consequently not merely signs pointing to a reality that is absent, but render present the personal reality of the saint or event imaged.

(19) How an icon is produced (i.e., written) is regulated by ecclesiastical tradition in the Eastern Orthodox and Eastern Catholic Churches, because an icon is believed to be a living expression of the Orthodox faith. In other words, an icon is not a piece of art, and the iconographer is not an artist, in the modern sense of the words "art" and "artist," because he is not trying to express his own ideas, nor is he trying to display his own natural talents. The iconographer is first and foremost creating a liturgical prayer, a window into heaven, and in order to do that he must live the Orthodox faith through prayer and fasting; while simultaneously following the aesthetic norms established by the Church's iconographic Tradition. Moreover, in writing an icon the iconographer is creating a specific memory (anamnesis) of an event or person within the life of the Church, a memory (anamnesis) that is identical to the memory (anamnesis) of the whole Church. Thus, an icon is a theophany, i.e., it is a manifestation of God through an eruption of divine energy into the world, which means that an icon really is what it signifies; and so, to touch an icon is to touch the personal reality of the mystery itself. Now taking into account what has already been said, if an iconographer were to depart from the aesthetic principles of the canonical iconographic tradition, it follows that the icons he writes would be unintelligable to an Orthodox Christian. An example of this can be seen by looking at a text written by an Orthodox hierarch, named Gregory Melissenos, who attended the Council of Florence in A.D. 1438:

The most important part of the quotation is the following phrase, "I do not know in what terms He [i.e., Christ] is inscribed." Clearly, by the 15th century the West had abandoned the notion of iconic inscription, which includes both the proper aesthetic approach to the writing of icons and their naming in order to make them canonical (i.e., to make them a visual expression of the Church's Rule of Faith). Now, what does it mean when an icon is described as being "canonical"? In this context the word "canonical" is a technical term that is meant to indicate that an icon is Orthodox, and that it may be venerated — with the approval of the proper ecclesiastical authorities — during the divine liturgy. To be canonical an icon must contain an identifying dedication with the name of the saint depicted in it, because the icon is connected to its heavenly prototype through a personal relation of name that allows the holy person to work through the icon as a means of spiritual encounter, while the icon must also follow the aesthetic principles of the ancient tradition. Thus, the name, along with the proper aesthetic perspective, are what make an image a holy icon. That said, if a dedication is missing from an image or if it does not conform to the aesthetic principles (i.e., the use of reverse perspective) of the canonical tradition, it follows that one cannot be sure who it is that is depicted in the image, nor can one know for what spiritual purpose the image has been made, because it has not been properly inscribed. Taking the above points into account, it becomes clear that the quotation was not intended as a polemical attack upon the West; instead, the quotation simply highlights the divergence between East and West in connection with the iconographic tradition, since the two sides no longer shared a common understanding of how a holy person or a sacred event is made manifest through an icon. For more information on icons I would recommend getting a copy of the book: The Meaning of Icons, by Leonid Ouspensky and Vladimir Lossky. Other helpful texts include Fr. Kucharek's book, The Byzantine-Slav Liturgy of St. John Chrysostom, and Leonid Ouspensky's two volume work entitled, Theology of the Icon.

(20) In the Eastern Churches the sacraments of initiation are not separated; and so, babies are baptized, chrismated with holy myron (confirmed), and receive first communion all during the same ritual service.

(21) The Eastern Churches believe that there are many holy mysteries (sacraments) in addition to the seven holy mysteries (sacraments) commonly celebrated liturgically by both East and West. 

(22) The human voice, according to the tradition of the Eastern Churches, is the only musical instrument allowed during liturgical celebrations, for as St. John Chrysostom wrote:  "David formerly sang songs, also today we sing hymns. He had a lyre with lifeless strings, the Church has a lyre with living strings. Our tongues are the strings of the lyre with a different tone indeed but much more in accordance with piety. Here there is no need for the cithara, or for stretched strings, or for the plectrum, or for art, or for any instrument; but, if you like, you may yourself become a cithara, mortifying the members of the flesh and making a full harmony of mind and body. For when the flesh no longer lusts against the Spirit, but has submitted to its orders and has been led at length into the best and most admirable path, then will you create a spiritual melody" [Exposition on Psalms, no. 41].

[C] Ecclesiological Differences

(23) The greatest ecclesiological difference of course concerns the place of the bishop of Rome within the Church. The Eastern Orthodox Churches reject any kind of primacy that places it in isolation from the synodal structure of the Church (i.e., from the universal episcopate). In this sense, primacy and synodality are held to be reciprocal realities [see Canon 34 of the Apostolic Constitutions].

and so it follows that:

(24) A Byzantine Orthodox ecclesiology of communion, which sees each local Church as the full realization of the one holy Catholic and Apostolic Church through the celebration of the Eucharistic Liturgy and the profession of the Orthodox faith under the guidance of a bishop in Apostolic Succession, is incompatible with the late medieval Roman universalist ecclesiology promoted by the Scholastics, which divides the Church into pieces that are only later juridically united through a concept of hierarchical subservience to the bishop of Rome.

Addendum on the Filioque

Eastern Triadology, unlike the Scholastic theology of the West, is focused first and foremost upon the monarchy of the Father, Who is seen as the sole principle (arche), source (pege), and cause (aitia) of divinity. Now, it follows from the doctrine of the monarchy of the Father that both the Son and the Holy Spirit receive their subsistence solely from Him, i.e., that He is their sole source and origin; and so, they are — as a consequence — one in essence (homoousios) with Him. Moreover, it is important to remember that the word homoousios itself, which was used by the First Ecumenical Council of Nicaea in order to describe the eternal communion of nature that exists between the Father and the Son, is a term that indicates a relation of dependence [see John Behr, The Nicene Faith, (Crestwood, NY:  St. Vladimir's Seminary Press, 2004), vol. 2, page 311; see also Christopher Beeley, Gregory of Nazianzus On The Trinity and The Knowledge of God, (Oxford:  Oxford University Press, 2008), page 213-214]. In other words, the use of the term homoousios by the Church Fathers involves recognition of the fact that the Son receives His existence as person (hypostasis) from God the Father alone by generation (gennatos), and that He is dependent upon the Father for His co-essential nature. That being said, it follows that the Son comes forth from the Father’s person (hypostasis), and not from the divine essence (ousia), which is always absolutely common to the three divine persons. The same also holds with the hypostatic procession (ekporeusis) of origin of the Holy Spirit, as opposed to His progression (proienai), because He also receives His existence from the Father alone, i.e., from the Father’s person (hypostasis), and not from the divine essence (ousia), which — as I already indicated — is absolutely common to the three divine persons [see St. Gregory Palamas, "Logos Apodeiktikos," I, 6]. Thus, it is from the Father Himself personally and directly that the other two persons of the Holy Trinity derive their eternal subsistence and their co-essential nature.  

Now, with the foregoing information in mind, it is clear that the Eastern Churches (both Orthodox and Catholic) must reject any theological system or theory that tries to elevate the Son to a co-principle of origin in connection with the existential procession (ekporeusis) of the Holy Spirit as person (hypostasis), because within Byzantine Triadology a theological proposition of that kind entails either the sin of ditheism, which involves positing the false idea that there are two principles or causes of divinity (i.e., the Father and the Son); or the heresy of Sabellian Modalism, which involves proposing the false notion that the Holy Spirit as person (hypostasis) proceeds from the Father and the Son "as from one principle," and thus causing an unintentional blending of the persons of the Father and the Son by giving the Son a personal characteristic (i.e., the power to spirate the Holy Spirit as person) that is proper only to the Father.

It is only in connection with the Spirit's progression (proienai), i.e., His outpouring as grace, that one may speak of a "filioque" of sorts (or to be more precise a "per filium"), but it must be made absolutely clear that the manifestation (phanerosis) of the Spirit as energy has nothing to do with His hypostatic procession (ekporeusis) of origin, which comes only from the Father as the sole principle (arche), source (pege), and cause (aitia) of divinity. The Eastern Church has never opposed the "per filium" in itself; instead, it has only rejected the notion that the "per filium" involves positing causality to the Son in connection with the Spirit's eternal origin (i.e., His subsistence). According to the Eastern Fathers the Spirit receives His subsistence from the Father alone through procession (ekporeuesthai), but they had no difficulty confessing that His presence is made manifest (phanerosis) through the Son. Sadly, at the Council of Florence the Latins insisted on the idea of causality being attributed to the Son and that is why the conciliar decree was immediately rejected by the vast majority of the Eastern Church when the bishops arrived back in Constantinople after the close of the council. Had the Latins not insisted on attributing causality to the Son it is likely that a real union could have taken place, and even held firm in spite of the collapse of Constantinople in A.D. 1453. It is to be lamented that the Latins were unwilling to accept the final proposal of the Eastern episcopal delegation, which rightly distinguished between the Spirit's procession of origin (ekporeuesthai) from the Father, and His gushing forth (anabluzein) through the Son.

Interestingly, the solution to this theological problem, which can be found in the Letter of St. Maximos to Marinus, was presented at the Council of Florence, but was unfortunately rejected by the West at the time. However, if the West could now accept what St. Maximus taught, namely, that ". . . the Father is the only cause (aition) of the Son and the Spirit, one by generation (gennesin) and the other by procession (ekporeusin)," it follows that the two sides could then make a common profession of faith in the Triune God. This solution would simply require the West to accept the difference between the hypostatic origin of the Holy Spirit, which comes only from the Father as the sole cause within the godhead and which safeguards the doctrine of the Father's monarchy, and the manifestation of the divine unity, which is revealed in the progression (proienai) of the energies of the Spirit from the Father through the Son.

Ultimately, any future agreement between the Roman Church and the Eastern Churches will no doubt have to be based upon an explicit rejection of the Florentine decree on the "filioque" and an acceptance of the Letter of St. Maximos to Marinus as normative in its place, with additional clarifications like the text below (or another one like it), which was written by Gennadios Scholarios:

"We Greeks confess and believe that the Holy Spirit proceeds (ekporeuesthai) from the Father, is proper to the Son and gushes forth (anabluzein) from Him, and we affirm and believe that He flows forth (procheisthai) substantially from both, namely from the Father through the Son."

Original Version:  21 July 2005 (from a thread at the Phatmass Phorum)

I have revised and expanded this outline over the years with the most recent revision completed on 17 March 2024.

Copyright © 2005-2024 Steven Todd Kaster