- Separate articles treat Eastern Orthodox Christianity, Oriental Orthodox Christianity, Lutheran Orthodoxy and Orthodox Judaism.
- For the book written by G. K. Chesterton see Orthodoxy (book).
The word orthodoxy, from the Greek ortho ('right', 'correct') and doxa ('thought', 'teaching', 'glorification'), is typically used to refer to the correct theological or doctrinal observance of religion, as determined by some overseeing body. The term did not conventially exist with any degree of formality (in the sense in which it is now used) prior to the advent of Christianity in the Greek-speaking world, though the word does occasionally show up in ancient literature in other, somewhat similar contexts. Orthodoxy is opposed to heterodoxy ('other teaching'), heresy and schism. People who deviate from orthodoxy by professing a doctrine considered to be false are most often called heretics, while those who deviate from orthodoxy by removing themselves from the perceived body of believers, i.e. from full communion, are called schismatics. Not infrequently these occur together. The distinction in terminology pertains to the subject matter; if one is addressing corporate unity, the emphasis may be on schism; if one is addressing doctrinal coherence, the emphasis may be on heresy.
Derived from late classical and medieval Christian apologetics for orthodoxy, more specifity is often applied when defending a claim to orthodoxy or refuting heresy. Apostasy, for example is a violation of orthodoxy that takes the form of abandonment of the faith, be it for some form of atheism or for some other faith, a concept largely unknown before the adoption of Christianity as the official religion of Rome. The first well-known apostate is probably Julian, the last pagan emperor of Rome. A lighter deviation from orthodoxy than heresy is commonly called error, in the sense of not being grave enough to cause total estrangement while yet seriously affecting communion. Sometimes error is also used to cover both full heresies and minor errors.
Religion embraces conceptualization of the divine and practice of worship, and how adherents of all faiths represent to others how they perceive these things, both from within and from without. In each there is a degree of openness, and an extent to which these elements are non-negotiable, in all religions. Tribal religions may involve cannibalising non-believers, or may be very open to theological discussion; while monotheistic religions adapt themselves to diverse cultures in manifold ways while yet not relinquishing certain precepts. Issues of tolerance and syncretism are distinct; a religion may tolerate another, neither oppressing nor adapting to it; a religion may permit itself to be absorbed into another; a religion may be outwardly intolerant while yet absorbing some teachings from another religion. A religion may be more tolerant of others at a given point in time than at another. These forms of cultural interplay impinge upon the extent to which a religion may or may not appear to maintain a consistent stance concerning its theology and practice.
The concept of orthodoxy is the most prevalent and even inherently pervasive in nearly all forms of organized monotheism, but orthodoxic belief is not usually overly emphasized in polytheistic or animist religions. Certainly, orthodoxy still exists and actively governs belief within these traditions, but in a much more flexible and limited way. Often there is little to no concept of dogma, and varied interpretation of doctrine and theology is tolerated and sometimes even encouraged within certain contexts. Syncretism, for example, plays a much wider role in non-monotheistic (and particularly, non-scriptual) religion. The prevailing governing idea within polytheism is most often orthopraxy ("right cultic practice") rather than "right belief".
Various groups have laid claim to the word orthodox as part of their titles, usually in order to differentiate themselves from other, 'heretical' movements. Orthodox Judaism focuses on a strict adherence to what it sees as the correct interpretation of the Oral Torah, dating from the revelation of the Torah on Mount Sinai. Within Christianity, the term occurs in the Eastern Orthodox, Western Orthodox, and Oriental Orthodox churches as well as in Protestant denominations like the Orthodox Presbyterian Church.
The Eastern Orthodox Churches hearken back to the original forms of worship; for example, the Nicene Creed is used as created at the First Council of Constantinople in 381, in contrast to the Roman Catholic church, which use the Nicene creed with the addition of the phrase 'and the Son' (see Filioque clause). This change is one of many causes for the Great Schism formalized in 1054 by simultaneous proclamations of "Anathema" from the collegial leadership of the Orthodox Churches in the East and the Bishop of Rome in the West. This emphasis on the use of the original "creed" is shared today by all Eastern Orthodox churches.
The Catholic Church considers the Eastern Orthodox to be in schism and therefore not in full communion with the Holy See. Some of Eastern Orthodox Christians in turn consider Roman Catholics to be heretics, while the majority consider them in schism.
Confusingly, the term "Western Orthodox" refers to Uniat Catholic churches in communion with the Roman See, known also as Eastern Catholic Churches. Actually this is rarely the case in semantic terms. Today "western Orthodox" will probably refer to groups of apostolic Orthodox Christians in the UK, USA, and perhaps smaller numbersin France, the Netherlands, Germany and Denmark, who wish to be Orthodox and yet want a western and Latin rite. In Ukraine and Romania there are Uniates called Greek Catholics who have Byzantine rite, but accept primacy of the Pope, and Papal infallibility, so they are Byzantine Catholics. Also in the Lebanon are groups called Maronites and Melkites in a smilar situation.
The Catholic Church considers all forms of Protestantism to be heresy or at the least, in error (since they do not have apostolic succession and thus their "rite" and ordinations are invalid); some Protestants are mutually hostile and consider Roman Catholics, and sometimes Eastern Orthodox, to be heretics. In some cases the term apostasy is applied within mutual invectives. The Catholic Church, since the Second Vatican Council, has been working harder to effect rapprochement among diverse forms of Christianity; these efforts have been met with wide-ranging responses. Some religious groups are considered by all of the aforementioned to be unorthodox (or even arbitrarily cults, as they are less commonly called in Protestant circles), including members of the Church of Jesus Christ of Latter Day Saints or Mormons, Jehovah's Witnesses, Unitarians, and some of the more radical forms of liberal theology.
Inside each of these ecclesiastical communities there are issues that correspond to estrangement or refinements of perceived orthodoxy. For example, the Roman See often issues recommendations as to what practices it considers orthodox so as to curb excesses or deficiencies by its prelates. Some evangelicals are pursuing innovations that other, more conservative evangelicals consider unorthodox and term "neo-evangelical," "neo-pentecostal," or "fringe Charismatic."
In English, the term "Oriental Orthodoxy" is used to refer to non-Chalcedonian eastern Christians, as opposed to Christians of Eastern Orthodox Churches, who accept the Council of Chalcedon (See Ecumenical Councils)and generally worship according to the Byzantine Rite. They are found in Egypt, Ethiopia, some parts of Syria, Iraq and Iran, Armenia,and southern India in Kerala State.They accept only the first three of the Oecumenical councils. In the last century there has been some rapproachement between these and the Eastern Orthodox Churches, particularly in Syria. There have been claims after dialogue, that really the differences have been of phraseology all along, and a simple misunderstanding of what each church holds. This is not entirely satisifactory to many Eastern Orthodox,and it is not considered in each church's competence to use a General Holy Synod to bring about communion. These Eastern Orthodox Christian hold that it would take another Great and Holy Council of every Eastern Orthodox Bishop together to reverse the Anathema, and this raises problems of its own.