Orthodoxy (from Greek orthos ("right", "true", "straight") + doxa ("opinion" or "belief", related to dokein, "to think"),) is adherence to accepted norms, more specifically to creeds, especially in religion. In the narrow Christian sense the term means "conforming to the Christian faith as represented in the creeds of the early Church".
Orthodoxy is opposed to heterodoxy ("other teaching") or heresy. People who deviate from orthodoxy by professing a doctrine considered to be false are called heretics, while those who, perhaps without professing heretical beliefs, break from the perceived main body of believers are called schismatics. The term employed sometimes depends on the aspect most in view: if one is addressing corporate unity, the emphasis may be on schism; if one is addressing doctrinal coherence, the emphasis may be on heresy.
Apostasy is a violation of orthodoxy that takes the form of complete abandonment of the faith. A deviation lighter 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.
The concept of orthodoxy is prevalent in many forms of organized monotheism, but orthodox belief is not usually overly emphasized in polytheistic or animist religions, in which there is often little or no concept of dogma, and varied interpretations of doctrine and theology are tolerated and sometimes even encouraged within certain contexts. Syncretism, for example, plays a much wider role in non-monotheistic (and particularly, non-scriptural) religion. The prevailing governing idea within polytheism is often orthopraxy ("right practice") rather than "right belief".
In classical Christian usage, the term orthodox refers to the set of doctrines which were believed by the early Christians. The Roman Emperor Constantine I initiated a series of Ecumenical Councils, also known as the First seven Ecumenical Councils, to try to formalize these doctrines. The most significant of these early decisions was that between the Homoousian doctrine of Athanasius and Eustathius (which became Trinitarianism) and the Heteroousian doctrine of Arius and Eusebius (called Arianism). The Homoousian doctrine, which defined Jesus as both God and man with the Hypostatic union of the 451 Council of Chalcedon, won out in the Church and was referred to as orthodoxy in most Christian contexts, since this was the viewpoint of the majority. (The minority Non-Trinitarian Christians object to this terminology).
Following the 1054 Great Schism, both the Western and Eastern churches continued to consider themselves uniquely orthodox and catholic. Over time the Western church gradually identified with the "Catholic" label and people of Western Europe gradually associated the "Orthodox" label with the Eastern church (in some languages the "Catholic" label is not necessarily identified with the Western church). In addition, there is a separate Oriental Orthodox communion, as well as other smaller communions that are commonly classified as "Orthodox".
See also 
- Belief in Jesus
- Eastern Orthodoxy
- Oriental Orthodoxy
- Orthodox Judaism
- Proto-orthodox Christianity
- Rule of Faith
- orthodox. Dictionary.com. Online Etymology Dictionary. Douglas Harper, Historian. Dictionary Definition (accessed: March 03, 2008).
- orthodox. Dictionary.com. The American Heritage Dictionary of the English Language, Fourth Edition. Houghton Mifflin Company, 2004. Dictionary definition (accessed: March 03, 2008).
- Liddell & Scott; Code of Justinian: "We direct that all Catholic churches, throughout the entire world, shall be placed under the control of the orthodox bishops who have embraced the Nicene Creed."
- Jostein Ådna (editor), The Formation of the Early Church (Mohr Siebeck 2005 ISBN 978-316148561-9), p. 342