Homoousion

 ( Trinitarianism ) 

From ὁμοούσιος (coessential), the theological term ὁμοουσιότης (coessentiality) was also derived. It was used by Greek-speaking authors, like Didymus of Alexandria and other theologians.

• Identity of substance between generator and generated.
• Identity of substance between things generated of the same substance.
• Identity of substance between the partners of a syzygy.

Origen seems to have been the first ecclesiastical writer to use the word in a nontrinitarian context, but it is evident in his writings that he considered the Son's divinity lesser than the Father's, since he even calls the Son "a creature".. It was by Athanasius of Alexandria and the Nicene Council that the Son was taken to have exactly the same essence with the Father, and in the Nicene Creed the Son was declared to be as immutable as his Father..

While it is common to find statements that Origen and other early apologist Church fathers held Subordinationism views, Ilaria Ramelli discussed the "anti-subordinationism" of Origen.

Both the Nicene and Athanasian Creed creeds affirm the Son as both begotten of, and equal to his Father. If so, many concepts of the Holy Trinity would appear to have already existed relatively early while the specific language used to affirm the doctrine continued to develop.

Some theologians preferred the use of the term ὁμοιούσιος ( or alternative uncontracted form ὁμοιοούσιος ; from ὅμοιος, , "similar", rather than ὁμός, , "same, common"), , , . in order to emphasize distinctions among the three persons in the Godhead, but the term became a consistent mark of Nicene orthodoxy in both East and West. According to this doctrine, Jesus Christ is the physical manifestation of Logos (or the Word), and consequently possesses all of the inherent, ineffable perfections which religion and philosophy attribute to the God. In the language that became universally accepted after the First Council of Constantinople in AD 381, three distinct and infinite hypostases, or divine persons, the Father, the Son, and the Holy Spirit, fully possess the very same divine .

This doctrine was formulated in the 4th century, during the Arian controversy over Christology between Arius and Athanasius. The several distinct branches of Arianism which sometimes conflicted with each other as well as with the pro-Nicene homoousian creed can be roughly broken down into the following classifications:

• (from ὅμοιος, , "similar", as opposed to ὁμός, , "same, common"), which maintained that the Son was "like in substance" but not necessarily to be identified with the essence of the Father.
• Homoeanism (also from ὅμοιος), which declared that the Son was similar to God the Father, without reference to substance or essence. Some supporters of Homoean formulae also supported one of the other descriptions. Other Homoeans declared that the father was so incomparable and ineffably transcendent that even the ideas of likeness, similarity or identity in substance or essence with the subordinate Son and Holy Spirit were heretical and not justified by the Gospels. They held that the Father was the Son in some sense but that even to speak of was impertinent speculation.
• Heteroousianism (including Anomoeanism), which held that God the Father and the Son were different in substance and/or attributes.

All of these positions and the almost innumerable variations on them which developed in the 4th century were strongly and tenaciously opposed by Athanasius and other pro-Nicenes, who insisted on the doctrine of or consubstantiality, eventually prevailing in the struggle to define this as a dogma of the still-united Western and Eastern churches for the next two millennia when its use was confirmed by the First Council of Constantinople (381). The struggle over the understanding of Christ's divinity was not solely a matter for the Church. The Roman emperor Theodosius I had published an edict, prior to the Council of Constantinople, declaring that the Nicene Creed was the legitimate doctrine and that those opposed to it were heretics.Theodosian Code 16:2, 1 Friell, G., Williams, S., Theodosius: The Empire at Bay, London, 1994.

It has also been said that the term , which Athanasius favored and which was ratified in the Nicene Council and Creed, was actually a term reported to also be used and favored by the Sabellianism in their Christology. It was a term with which many followers of Athanasius were actually uncomfortable. The so-called Semi-Arians in particular objected to it. Their objection to this term was that it was considered to be "un-Scriptural, suspicious, and of a Sabellian tendency.". This was because Sabellius also considered the Father and the Son to be "one substance", meaning that, to Sabellius, the Father and the Son were "one essential Person", though operating in different faces, roles, or modes. This notion, however, was also rejected at the Council of Nicaea, in favor of the Nicene Creed, which holds the Father and Son to be distinct yet also coequal, coeternal, and consubstantial divine persons.

The use of the word homoousios in the Nicene Creed was proposed by Emperor Constantine I, who convened and chaired the First Council of Nicea. By persuasion and by threats of excommunication and exile, Constantine obtained the endorsement of all but two of the attending bishops for the inclusion of the word.

• Consubstantiality
• Hypostatic union

• (2025). 9780227900086, James Clarke & Co. . ISBN 9780227900086
• James Bethune-Baker (2025). 9781592448982, The University Press. . ISBN 9781592448982
• Georges Florovsky (1987). 9783905238075, Büchervertriebsanstalt. . ISBN 9783905238075
• Michael J. Loux (2025). 9780801474880, Cornell University Press. . ISBN 9780801474880
• István Pásztori-Kupán (2025). 9781134391769, Routledge. . ISBN 9781134391769
• Mark Weedman (2025). 9789004162242, Brill. . ISBN 9789004162242

• .
• .