Metousiosis is a Greek term () that means a change of ousia (, "essence, inner reality").
Cyril Lucaris (or Lucar), the Patriarch of Alexandria and later of Constantinople, used this Greek term to express the idea for which the Latin term is transsubstantiatio (transubstantiation), which likewise literally means a change of substantia (substance, inner reality), using, in the 1629 Latin text of his The Eastern Confession of the Orthodox Faith, the term transsubstantiatio, and, in the Greek translation published in 1633, the term .
To counter the teaching of Lucaris, who denied transsubstantiatio/, Metropolitan Petro Mohyla of Kiev (also called Peter Mogila) drew up in Latin an Orthodox Confession, defending transubstantiation. Translated into Greek, using "" for the Latin term "transubstantiation", this Confession was approved by all the Greek-speaking Patriarchs (those of Constantinople, Alexandria, Antioch, and Jerusalem) in 1643, and again by the Synod of Jerusalem (1672) (also referred to as the Council of Bethlehem).
The declaration of the 1672 Orthodox Synod of Jerusalem is quoted by J.M. Neale (History of Eastern Church, Parker, Oxford and London, 1858) as follows: "When we use the word metousiosis, we by no means think it explains the mode by which the bread and wine are converted into the Body and Blood of Christ, for this is altogether incomprehensible ... but we mean that the bread and wine are changed into the Body and Blood of the Lord, not figuratively or symbolically, nor by any extraordinary grace attached to them ... but ... the bread becomes verily and indeed and essentially the very true Body of the Lord, and the wine the very Blood of the Lord."
The Catechism of the [Roman] Catholic Church similarly states that the change is real while averring that the means of change remain a mystery: "The signs of bread and wine become, in a way surpassing understanding, the Body and Blood of Christ."
Since the Eastern Orthodox Church accepts as dogma only the solemn teaching of seven Ecumenical Councils, this approval, though part of what the Encyclopædia Britannica called "the most vital statement of faith made in the Greek Church during the past thousand years", was not equivalent to a dogmatic definition. However, the Protestant scholar Philip Schaff wrote in his Creeds of Christendom: "This Synod is the most important in the modern history of the Eastern Church, and may be compared to the Council of Trent. Both fixed the doctrinal status of the Churches they represent, and both condemned the evangelical doctrines of Protestantism ... the Romish doctrine of transubstantiation (, ) is taught as strongly as words can make it."
The term metousiosis is, of course, not found in the text of the Eastern Orthodox Church's Divine Liturgy, just as the term transubstantiation is not found in the text of the Latin Eucharistic liturgy. The Encyclopedia of Eastern Orthodox Christianity states: "The Greek term metousiosis, which is comparable to the Latin transsubstantiatio, does appear in Orthodox liturgical and theological texts - though not as often as other vocabulary (e.g., metastoicheiosis, a "change of elements").
A. Osipov states that the Orthodox use of the Greek word (metabole), meaning "change", and the Russian ? in relation to the Eucharist should not be taken as equivalent to the word "transubstantiation", which has been rendered as metousiosis. Eastern theologians who use the word "transubstantiation" or "metousiosis" are careful to exclude the notion that it is an explanation of how the bread and wine of the sacrament are changed into the body and blood of Christ, instead of being a statement of what is changed. Both Orlov and Nikolaj Uspenksij appeal to Church Fathers who, when speaking of other doctrines, drew analogies from the Eucharist and spoke of it as bread and wine, but as having also a heavenly nature.
Some Eastern Orthodox theologians thus appear to deny transubstantiation/metousiosis, but in the view of Adrian Fortescue, what they object to is the associated theory of substance and accident, and they hold that there is a real change of the bread and wine into the body and blood of Christ.
An English translation of the full, quite lengthy, declaration by the 1672 Orthodox Council of Jerusalem, convoked by Patriarch Dositheos II of Jerusalem, can be found at the website Chapter VI of Acts and Decrees of the Synod of Jerusalem.
The first edition of The Longer Catechism of the Orthodox, Catholic, Eastern Church, known also as The Catechism of St. Philaret, did not include the term metousiosis; but it was added in the third edition: "In the exposition of the faith by the Eastern Patriarchs, it is said that the word transubstantiation is not to be taken to define the manner in which the bread and wine are changed into the Body and Blood of the Lord; for this none can understand but God; but only thus much is signified, that the bread truly, really, and substantially becomes the very true Body of the Lord, and the wine the very Blood of the Lord." The official Greek version of this passage (question 340) uses the word "metousiosis".
Writing in 1929, Metropolitan of Thyatira Germanos said that an obstacle to the request for union with the Eastern Orthodox Church presented in the 17th century by some Church of England bishops was that "the Patriarchs were adamant on the question of Transubstantiation", which, in view of the Thirty-Nine Articles, the Anglican bishops did not wish to accept.
A collection of texts from as early as the 5th century in which councils, individual ecclesiastics, and other writers and theologians of the Eastern Orthodox Church used the Greek term in the same sense as the Latin term is found at Orthodoxy and Transubstantiation.
The Coptic Orthodox Church of Alexandria does not use a term corresponding to transubstantiation/metousiosis, but it speaks of "change" and rejects the Protestant denial of "the reality of the change of the bread and wine to the body and the blood of our Lord Jesus Christ".