Homoousion

Homoousion (/ˌhɒmoʊˈuːsiɒn, ˌhoʊm-/ HO(H)M-oh-OO-see-on; Ancient Greek: ὁμοούσιον, lit. 'same in being, same in essence', from ὁμός, homós, "same" and οὐσία, ousía, "being" or "essence") is a Christian theological term, most notably used in the Nicene Creed for describing Jesus (God the Son) as "same in being" or "same in essence" with God the Father (ὁμοούσιον τῷ Πατρί). The same term is also applied to the Holy Spirit in order to designate him as being "same in essence" with the Father and the Son. Those notions became cornerstones of theology in Nicene Christianity, and also represent one of the most important theological concepts within the Trinitarian doctrinal understanding of God.

The term ὁμοούσιον (homoousion), the accusative case form of ὁμοούσιος (homoousios, "consubstantial"), was adopted at the First Council of Nicaea (325) in order to clarify the ontology of Christ. From its Greek original, the term was translated into other languages. In Latin, which is lacking a present participle of the verb 'to be', two main corresponding variants occurred. Since the Aristotelian term ousia was commonly translated in Latin as essentia (essence) or substantia (substance), the Greek term homoousios was consequently translated into Latin as coessentialis or consubstantialis, hence the English terms coessential and consubstantial. Some modern scholars say that homoousios is properly translated as coessential, while consubstantial has a much wider spectrum of meanings. The Book of Common Prayer renders the term as "being of one substance with the Father."

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.

The term ὁμοούσιος had been used before its adoption by the First Council of Nicaea. The Gnostics were the first to use the word ὁμοούσιος, while before the Gnostics there is no trace at all of its existence.^{[excessive citations]} The early church theologians were probably made aware of this concept, and thus of the doctrine of emanation, taught 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 says 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.

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.

The Nicene Creed is the official doctrine of most Christian churches—the Catholic Church, Eastern Orthodox Church, Oriental Orthodox Churches, Church of the East, Lutheran Churches, Moravian Church, Anglican Communion, and Reformed Churches as well as other mainline Protestant and evangelical 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 homoousios 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.