Where did substance language enter the Trinity debate?

Question

The Bible does not describe God and His Son in terms of substance. The closest we get is Hebrews 1:3, where the Son is described as the mirror image of the hypostasis of God. At the time, hypostasis still had the same meaning as ousia (substance), as it also had in the 325 AD Nicene Creed. Therefore the NASB translates hypostasis as "substance" in Hebrews 1:3.

The Wikipedia page Sabellianism states that the Gnostics were the first to use the word in connection with their doctrine of emanation in which the generator and the generated have the same substance. Were these people also Christians? Did they perhaps bring substance language into the church debate?

The dates of the theologians that used the word substance, as I could gather from Wikipedia, in their apparent chronological sequence, are as follows:

• Praxeas lived at the end of the 2nd century/beginning of the 3rd century.
• Tertullian (155-220) - In Against Praxeas, Tertullian often refers to substance. Did he get it from Praxeas?
• Sabellius flourished about AD 215 - Prof Ninan stated that Sabellius used the word homoousian.
• Noetus was a presbyter around AD 230
• Origen (184-253) - According to his Wikipedia page, he rejected the belief that the Son and the Father were one hypostasis as heretical. But that implies that somebody was using that language before him. That would include Tertullian.

So, these people all lived more or less at the same time but given the early date for Tertullian, and since he wrote Against Praxeas, I assume Praxeas was the first of the authors. Is it possible that he was one of the gnostics and that he introduced the word substance into the debate?

Answer 1

The term ὁμοούσιον (homoousion) predates Dionysius Bishop of Alexandria (r. 247-265 A.D.), who wrote in response to a c. 262 A.D. letter to him by Pope St. Dionysius (259-268 A.D.):

I have not found this term (ὁμοούσιος τῷ Θεῷ) any where in Holy Scripture, yet my remarks which follow, and which they have not noticed, are not inconsistent with that belief

^{cf. Pohle The Divine Trinity: A Dogmatic Treatise pt. 1, ch. 2, §1, a. 2. "Its [Sabellianism's] Condemnation."}

Tertullian [b. c. 160 A.D.] had already used the Latin equivalent of Homoousion, conceding to [his contemporary] Praxeas the Sabellian that the Father and the Son were unius substantiæ, of one substance, but adding duarum personarum, of two persons (Adv. Prax., xiii).
[…]
Origen [b. 185, d. c. 253-4], who is, however, inconsistent in his vocabulary, expressed the anti-Sabellian sense of Dionysius of Alexandria by calling the Son "Heteroousion".
_{—Bridge, J. (1910). Homoousion. In The Catholic Encyclopedia. New York: Robert Appleton Company.}

Answer 2

Where did substance language enter the Trinity debate ?

Since the belief in both God and his Son is a basic Christian tenet, the question naturally arises as to what exactly is meant by it:

• Is God Christ's father in the same sense in which He is also ours, namely as creator ?
• Or is He his father in the fullest sense of the word, namely as procreator ?

Since the difference between actual offspring, and metaphorical ones, is that the former literally share one's flesh and blood (or DNA, in modern parlance), a concept had to be sought to express the same idea in more abstract terms, as the divine is ultimately immaterial.

The Wikipedia page Sabellianism states that the Gnostics...

Sabellianism and Gnosticism are not (meaningfully) related to one another.

the generator and the generated have the same substance

They don't. In Gnosticism, the emanated is (ontologically) inferior to the emanator, the last (and therefore most inferior) emanation being the physical (and therefore intrinsically evil) world (this represents the fundamental Gnostic belief).

Were these people also Christians ?

Gnosticism was a highly syncretic, but ultimately independent, belief system, interacting with various other ancient religions, such as Platonism, Judaism, Christianity, or Zoroastrianism. At its roots, however, it was no more Christian than either pagan Platonism, or Judaism proper (which also interacted with one another, as evidenced by both the Septuagint Apocrypha, as well the writings of Philo, for instance).

Sabellius used the word homoousi[os].

Technically true, but its meaning was diametrically opposed to Nicaea's usage of the same term. It is like I were to tell you that English and German are related languages, and that both use the term Gift, but I would conveniently omit to inform you that, in German, it means poison, not present, as it does English.

Is it possible that [Praxeas] was one of the Gnostics [?]

No. Unitarianism is not Gnosticism.

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The closest thing, within Christianity itself, that I could (meaningfully) compare Gnosticism with, is Pseudo-Dionysius' system of angelic hierarchies.