According to the Nicean Creed, Jesus Christ is said to be:

Light of Light, true God of true God, begotten and not made; of the very same being (ὁμοούσιον) of the Father, by Whom all things came into being, in heaven and on earth, visible and invisible.

φῶς ἐκ φωτός, Θεὸν ἀληθινὸν ἐκ Θεοῦ ἀληθινοῦ, γεννηθέντα οὐ ποιηθέντα, ὁμοούσιον τῷ Πατρί, δι' οὗ τὰ πάντα ἐγένετο

How was the idea of homoousion developed, and when was this term used prior to the Council of Nicea?


This seems to have been prompted by Greek Philosophy beginning about 600 BC. This is most pronounced in the teachings of Plato, specifically his Theory of Forms in Plato's cave allegory.


In Plato's theory, εἶδος (eidos) represents the "Visible Form" while, μορφή (morphē) represents the "shape". Additionally, within Greco-Roman philosophy, there were also the φαινόμενα (phainomena), "appearances" which underwent significant philosophical discussion.

In Plato's allegory, Plato asks Glaucon to imagine a prisoner in a cell in a dungeon or cave. Out of view of the prisoner is a light source. This light source illuminates an object - again out of view of the prisoner. The prisoner in the cave is only able to see the shadow cast by the object:

Allegory of the Cave

In terms of the Allegory, the εἶδος (eidos) is the object or vase while the μορφή (morphē) is the projected image of the object, or the shadow of the vase.

As Wikipedia notes,

The English word "form" may be used to translate two distinct concepts that concerned Plato—the outward "form" or appearance of something, and "Form" in a new, technical nature, that never

...assumes a form like that of any of the things which enter into her; ... But the forms which enter into and go out of her are the likenesses of real existences modelled after their patterns in a wonderful and inexplicable manner....

The objects that are seen, according to Plato, are not real, but literally mimic the real Forms.

So in terms of God, the form of God as it appears to us (where we are the prisoner in Plato's cave) is the μορφή (morphē). This term acknowledges that our ability to view God is imperfect, and we are not capable of truly seeing God fully and directly. In trinitarian thought, the incarnation of Jesus might be thought of in some contexts as μορφή (morphē) - as Jesus, that was how God was able to appear to us.

Conversely, God's true form could be thought of as εἶδος (eidos). It holds the concept of God's true and actual form which we lack the ability and perspective to view properly due to our humanly limitations.

The Bible books of John and Philippians appear to reference this as do many other passages, I am sure:

who, though he was in the form [morphe] of God, did not count equality with God a thing to be grasped (Philippians 2:6 ESV).

And the Father who sent me has himself borne witness about me. His voice you have never heard, his form [eidos] you have never seen, (John 5:37 ESV)

Similarly, the Holy Spirit at Pentecost might be thought to be the φαινόμενα (phainomena) of God.

So, how do we get from form to substance?

The obvious problem for the philosopher here is that if Jesus is merely the form (morphē) of God, then he is not truly God. If Jesus is form (morphē) then he is not εἶδος (eidos). If the holy spirit is a φαινόμενα (phainomena) then she is not εἶδος (eidos).

This presents a problem for the Trinitarian scripturally, with Jesus's claims to be God.

This can then easily be corrected by asking "well, what if Jesus, the Holy Spirit and God are different forms, but are all of the same substance?" What if Jesus is but is a different form (morphē) of God, but is ὁμοούσιος (Homooúsios) as God?

Vs-à-vis Gnosticism

While Aristotle was known for using the term οὐσία to describe his philosophical concept of Primary Substances, the term ὁμοούσιος (Homooúsios) is first used by the Gnostics to describe their doctrine of Emanations, a concept that supported the idea of Aeons - a Panentheistic idea that we all worship the same God which simply appears in different forms (but these gods are also ὁμοούσιος [Homooúsios] or of the same substance as God). In contrast Sabellianism believed that God was singular and not triune, while Gnosticism taught god was polyune. According to Sabellianism, God is only one indivisible being and nothing can be of the same substance as God - he can only be taking on a different role or mode when he acts as the Holy Spirit or as Jesus.


From this context, we can easily see how we arrive at the Arian Controversy after this issue was raised and brought to the public attention by the Gnostics and philosophers. With this background in place, it is clear that when the language of Plato's Theory of Forms is used to describe Jesus as a form of God, it lends itself to the idea that Jesus is not God, but is merely a shadow or projection of God - not God himself. The language and concept of οὐσία therefore became necessary for the Trinitarians to explain both how Jesus could be both a form of God and BE God.

  • Thank you for the answer James. (+1) definitely. I didn't know Plato's cave was relevant. But could you explain what the gnostics have to do with this? I thought the gnostics were heretical groups, so what is their connection with the trinitarians? Three different forms as one god sounds exactly like Sabellianism.
    – Cannabijoy
    Feb 2 '17 at 13:43
  • @anonymouswho I have updated this answer to more directly address your question about Gnosticism and Sabellianism. Note that this answer largely sources from here Feb 5 '17 at 8:18
  • This looks great James. Thank you. Answer accepted and bounty is yours!
    – Cannabijoy
    Feb 6 '17 at 6:39

The root of ὁμοούσιον ("one substance") is the word οὐσία ("substance"). The other key word in the Nicene Creed is "hypostasis", which mentioned together with "substance" in the anathemas:

But as for those who say, There was when He was not,
and, Before being born He was not,
and that He came into existence out of nothing,
or who assert that the Son of God is of a different hypostasis [ὑπόστασις]
or substance [οὐσία],
or created,
or is subject to alteration or change
- these the Catholic and apostolic Church anathematizes.

In New Testament usage, substance/οὐσία is translated as "goods" (Luke 15:12) or "substance" (Luke 15:13) in the King James Version, and in modern versions as "property" (RSV, ESV), "estate" (NASB, NIV), and "wealth" (NIV). Hypostasis/ὑπόστασις in the KJV is related as "confidence" (2 Corinthians 9:4, 11:17 and Hebrews 3:14), (confusingly) "substance" (Hebrews 11:1), and "of [his] person" (Hebrews 1:3). Modern versions also render the word as "confident/confidence" (RSV, ESV, NASB, NIV), "conviction" (RSV, NIV), "assurance" (ESV, NASB), as well as "of [his] nature" (RSV, ESV, NASB) and "of [his] being" (NIV).

These two words have very particular theological meanings, however, in the context of the Nicene-Creed, where they were used not only to combat the Arian heresy, but also to clarify the very nature of the Trinity. Michael Pomazansky attempts to explain the development of both terms in the Nicene context as follows:

In earliest Christian times, until the Church’s faith in the Oneness of Essence and the equality of the Persons of the Holy Trinity had been precisely formulated in strictly defined terminology, it happened that even those Church writers who were careful to be in agreement with the universal consciousness of the Church and had no intention to violate it with any personal views of their own, sometimes, together with clear Orthodox thoughts, used expressions concerning the Divinity of the Persons of the Holy Trinity which were not entirely precise and did not clearly affirm the equality of the Persons.

This can be explained, for the most part, by the fact that in one and the same term some shepherds of the Church placed one meaning and others, another meaning. The concept of “essence” was expressed in the Greek language by the word ousia, and this word was in general understood by everyone in the same way. Using the word ousia, the Holy Fathers referred it to the concept of “Person.” But a lack of clarity was introduced by the use of another word, “Hypostasis.” Some signified by this term the “Persons” of the Holy Trinity, and others the “Essence.” This circumstance hindered mutual understanding. Finally, following the authoritative example of St. Basil the Great, it became accepted to understand by the word Hypostasis the Personal attributes in the Triune Divinity.

Orthodox Dogmatic Theology, p. 94-95

  • Thank you Dialogist. This is a great answer, except I'm only looking for usages of the term ὁμοούσιον and not the words associated with it. The actual word itself is not in the NT (but that's okay because neither is trinity, or eternally begotten, or incarnation, or God the Son, or consubstantial, ect), and I'm wondering how this term became accepted as Christian doctrine.
    – Cannabijoy
    Sep 1 '16 at 13:56
  • I do think the root word is what's important here, but thanks. That is what had a novel meaning imputed to it.
    – user22553
    Sep 1 '16 at 13:58

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