Homoousion

Pre-Nicene usage

The term ὁμοούσιος had been used before its adoption by the First Council of Nicene. The Gnostics were the first to use the word ὁμοούσιος, while before the Gnostics there is no trace at all of its existence. The early church theologians were probably made aware of this concept, and thus of the doctrine of emanation, by the Gnostics. In Gnostic texts the word ὁμοούσιος is used with the following meanings:

For example, Basilides, the first known Gnostic thinker to use ὁμοούσιος in the first half of the 2nd century AD, speaks of a threefold sonship consubstantial with the god who is not. The Valentinian Gnostic Ptolemy claims in his letter to Flora that it is the nature of the good God to beget and bring forth only beings similar to, and consubstantial with, himself. The term ὁμοούσιος was already in current use by the 2nd-century Gnostics, and through their works it became known to the orthodox heresiologists, though this Gnostic use of the term had no reference to the specific relationship between Father and Son, as is the case in the Nicene Creed.

Adoption in the Nicene Creed

The Nicene Creed is the official doctrine of most Christian churches – the Catholic Church, Eastern Orthodox Church, Oriental Orthodox churches, Church of the East, and Anglican Communion, as well as Lutheran, Reformed, Evangelical, and most mainline Protestant churches – with regard to the ontological status of the three persons or hypostases of the Trinity: Father, Son and Holy Spirit.

Origen seems to have been the first ecclesiastical writer to use the word ὁμοούσιος 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 nature or essence with the Father, and in the Nicene Creed the Son was declared to be as immutable as his Father.

Some theologians preferred the use of the term ὁμοιούσιος (homoioúsios, from ὅμοιος, hómoios, "similar", rather than ὁμός, homós, "same") in order to emphasize distinctions among the three persons in the Godhead, but the term ὁμοούσιος 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 Supreme Being. 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 ousia.

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:

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 homoousion or consubstantiality, eventually prevailing in the struggle to define the dogma of the still-united Catholic and Eastern Orthodox churches for the next two millennia when its use was confirmed by the First Council of Constantinople. The struggle over the definition of the nature of Christ's divinity was not solely a matter for the Church. The Roman Emperor Theodosius 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.

It has also been noted that this Greek term ὁμοούσιος, 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 Sabellians 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 the word ὁμοούσιος. 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 Son were "one essential Person", though operating as different faces, roles, or modes. This notion, however, was also rejected at the Council of Nicaea, in favor of the Athanasian Creed, which holds the Father and Son to be distinct yet also coequal, coeternal, and consubstantial divine persons.