Update: I originally wrote this series of posts in 2015 and since then I have changed my view. I’ve decided to keep the posts live, but wish to add that caveat at the outset.
In this fourth post I consider whether a subordination which is eternal and functional must by definition also be ontological. Follow the links to read the first, second and third posts of this series.
Ontology, Order and Obedience
One of the key non-Subordinationist arguments is that ‘a subordination that extends into eternity cannot remain only functional but […] becomes ipso facto an ontological reality.’ Giles writes,
Once the word eternal is used, it indicates that the subordination ascribed defines the person. If the Son of God is eternally subordinated in function, and cannot be otherwise, then in his being/essence/nature/substance he is in some way less than the Father.’ 
Such a notion of eternal rank would indeed be heretical, a point which Letham readily admits. Nonetheless Subordinationists argue that it is possible to acknowledge authority and obedience within the immanent Trinity without implying rank.
I would question whether it is legitimate for non-Subordinationists to claim that ‘eternal’ necessarily means ‘ontological.’ Bilezikian writes, ‘since the attribute of eternity inheres in the divine essence, any reality that is eternal is by necessity ontologically grounded. Eternity is a quality of existence.’ Orthodox Trinitarianism states that God is one with respect to ousia and physis (substance and nature) but three with respect to prosopa, hypostases and tropos hyparxeos (persons, modes of subsistence and modes of being). By saying that eternal must imply ontological, Bilezikian and Giles essentially collapse ousia and physis into prosopa, hypostases and tropos hyparxeos, thus making it impossible for there to be such a thing as any eternal distinction between members of the Trinity.
To hold that Father and Son are distinct in ousia or physis would imply polytheism, whilst to hold that they are not eternally distinct in prosopa, hypostases and tropos hyparxeos would imply Modalism. If Subordinationists risk the former of these errors, non-Subordinationists risk the latter. Surely we must be able to say that the Father and Son can be eternally distinct in prosopa but not in ousia, or Trintarian theology becomes impossible.
I agree with Letham that the non-Subordinationist position, by denying that the economic Trinity accurately reveals an eternal authority-obedience relationship between the Father and Son risks Modalism.
Non-Subordinationists also argue that ‘in traditional, orthodox theology “will” is attached to “nature”’ and therefore ‘if each divine person has his own will, the unity of the one Godhead is destroyed.’ If will is attached to nature, Subordinationism is heretical at worst, or nonsensical at best.
I question whether it is fair to say that ‘will’ is a property of ousia and physis rather than prosopa, hypostases and tropos hyparxeos? Cunningham writes that ‘the Three are never in essential conflict with one another, yet such conflict must be theoretically possible because of their difference.’ Yet what makes conflict possible if not a distinction of will? Cunningham continues,
God is capable of being internally conflicted, but chooses otherwise […] This notion of God’s interior peaceableness is echoed throughout the early period of Christian theological reflection. […] According to [St Gregory Nazianzus] monarchy or monotheism is not defined as “the sovereignty of a single person […]” but rather “the single rule produced by equality of nature, harmony of will, identity of action, and the convergence toward their source of what springs from unity.” Note especially the phrase “harmony of will”: the description here is not of a narrow monism, but of difference that is nevertheless brought into some form of polyphonic agreement.’ 
This is not to suggest that non-Subordinationists deny any distinction between the persons in the immanent Trinity. Olson writes
The Great Church as a whole (both East and West including the magisterial Protestant Reformers) believed in a hierarchy within the immanent Trinity […] If in the economic Trinity we see […] a subordination of the Son to the Father there must also be subordination of the Son to the Father in the immanent Trinity’ 
He is adamant however that such a hierarchy ‘has nothing to do with authority over, which, if imported into the immanent Trinity, would imply a kind of Subordinationism.’ Non-Subordinationists acknowledge many ways in which orthodox Trinitarianism affirms divine order (taxis); for example sequential revelational order, in which ‘the Father is introduced first as the creator, the Son is mentioned next primarily in relation to his work of revelation and redemption, and last the Spirit is said to be given to all believers after Christ’s ascension.’ Again, we must be cautious not to overstate this, lest by correlating too tightly Father with Creation, Son with redemption and Spirit with new birth we risk Modalism. Rather, as Basil writes, ‘Each act of God is initiated by the Father, effected by the Son, and perfected by the Spirit.’ Since Athanasius, orthodox theologians have spoken of not only revelational, but operational order among the divine persons. In Creation, the Father speaks and Creation is achieved through the Son, with the Spirit sustaining and manifesting God’s immediate presence in His creation. In Redemption, the Father sends the Son who, by his obedience, accomplished redemption, which is applied to us by the Spirit.
Thirdly, orthodox theologians spoke of an order of relationship; we relate to the Father, through the Son, in the Spirit. And fourthly, there is order in differing origination. Gregory of Nazianzus speaks of ‘the unbegottenness of the Father […] the generation of the Son and the procession of the Spirit.’ As Giles notes ‘These terms are all metaphors that defy precise definition. Nevertheless, all orthodox theologians agree that the word begotten does not mean created, or created in time. The words begotten and proceeding speak of eternal generation, and thus differing relations of origin.’ Olson considers this fourth form of taxis to be primary, especially in the Cappadocian Fathers, who ‘carefully distinguished between the monarchy of the Father and Arian Subordinationism’ and spoke of the monarchy of the Father ‘in the sense that the Father is the fount of divinity from which the Son is begotten (not made) and the Holy Spirit proceeds.’
In addition, Subordinationists argue that there is evidence for an eternal authority-obedience relationship between the Father and Son. Horrell has proposed a social model of the Trinity in which ‘the one divine Being eternally exists as three distinct centres of consciousness, wholly equal in nature, genuinely personal in relationships, and each mutually indwelling the other.’ He argues that the egalitarian conceptions of the immanent Trinity that typically accompany a social model do not find sufficient mooring in Scripture. He writes, ‘Ontological equality of the members of the Godhead and reciprocal indwelling of each in the other does not necessarily preclude eternal relational order.’ In Scripture we see ‘the generous pre-eminence of the Father, the joyous collaboration of the Son, and the ever-serving activity of the Spirit’, though he concedes ‘it is most difficult for us philosophically to hold full equality of nature together with eternal differences in communal order.
In fact, Horrell concludes that,
A social model of the Godhead that does not recognize eternal differentiation of the Father, Son, and Holy Spirit based firmly in divine revelation easily loses all significant distinction. An egalitarian model of the immanent Godhead collapses Trinitarian distinctions. Conversely, an eternally ordered social model of the Trinity argues that the activities and roles of each member visible throughout divine revelation are analogously correspondent with the immanent triune relationships.’ 
Both Subordinationists and non-Subordinationists look to the creeds and historical theologians for support; non-Subordinationists claiming that such sources provide no support whatsoever for the eternal subordination of the Son. Some Subordinationists who embrace a narrow view of taxis interpret in error any hint of order as necessarily implying an authority-obedience subordination, whilst non-Subordinationists downplay texts that do in fact speak of the eternal obedience of the Son. In the next post I shall seek to demonstrate the latter through two brief examples from Augustine and Barth.
 Bilezikian, (1997) 63
 Giles, (2006) p57, also p30
 Letham, (2004) p482, 484
 Bilezikian, (1997) p63
 Letham, (1999) p68
 Olson, (2011c)
 Giles, (2006) p30; also p62
 See Olson’s conclusion (2011c)
 Cunningham, (1998) p242
 Ibid., p242
 Although Grudem seems to read Bilezikian as denying absolutely any difference, (2004) p415-418
 Olson, (2011a)
 Giles, (2006) p50
 Horton, (2011) p301
 Quoted in Giles, (2006) p50. See similarly Calvin Institutes 1.13.18, p142-143 and Horton, (2011) p289, 301
 The Son: John 1:3; Col 1:6; Ps 33:6; 9; 1 Cor 8:6; Heb 1:2. The Spirit: Gen 1:2; Psalm 139:7
 The Father: John 3:16; Gal 4:4; Eph 1:9-10. The Son; John 6:38; Heb 10:5-7. The Spirit: John 3:5-8; 14:26; 15:26; 16:7; Rom 8:13; 15:16; 1 Pet 1:2
 Giles, (2006) p50
 Quoted in Allison, (2011) p240. See too Cunningham, (1998) p112
 Giles, (2006) p50
 Olson, (2011b)
 Olson, (2011c)
 Horrell, (2004) p408
 Ibid., p408
 Horrell, (2007) p45
 Horrell, (2004) p414
 Ibid., p414
 Ibid., p417
 See Giles (2006), in particular p35-41
 A trait I see evidenced particularly in Grudem, (2004)