Theologian Wayne Grudem, aside from his full-throated support for Donald Trump during the recent presidential election campaign, is known for another controversial position. He is a professor at Phoenix Seminary, and along with Southern Baptist Theological Seminary's Bruce Ware he has taught for some years that there is a relationship of subordination between the Father and the Son in the Trinity and that this mirrors the relationship between men and women – that is, women are under the authority of men.

They hold a "complementarian" view of male-female relations, which is a nice way of saying there are roles appropriate for men and roles appropriate for women; women shouldn't be pastors, for instance. Some take it even further – John Piper notoriously suggested to a woman that she shouldn't be a police officer because it would mean giving orders to men.

The subject has been much discussed in recent months, particularly following an attack on Grudem and Ware by Liam Goligher of the Alliance of Confessing Evangelicals, who said they had departed from historic Christianity and were "constructing a new deity".

A meeting of the Evangelical Theological Society in mid-November took the Trinity as its theme, and saw Grudem and Ware square off against two orthodox theologians, Kevin Giles and Millard Erickson. Giles – a renowned expositor of the doctrine of the Trinity and a thoroughgoing expert in the field – laid into Grudem and Ware in a style that was polite but devastating. His lecture, with a fascinating postscript, was posted on the Patheos website by Scot McKnight.

He acknowledges that "very large numbers of evangelicals" now believe the Grudem/Ware version of the Trinity. However, he says, it "contradicts what the Nicene creed, the Reformation and post-Reformation Protestant confessions and the ETS doctrinal statement teach". Furthermore, he says, "I want to state clearly and unambiguously that I think the doctrine of the Trinity has absolutely nothing to say about the relationship of the sexes." And, he adds: "My consistent argument for nearly twenty years has been that that if we evangelicals want to get right our doctrine of the Trinity, the primary and foundational doctrine of the Christian faith, we must sharply and completely separate out doctrine of the Trinity and our doctrine of the sexes. They are in no way connected and when they are connected both doctrines are corrupted."

Giles' lecture is quite long and densely argued, taking as its departure the Nicene Creed of 381 – which he says he believes not because it is a creed but because it expresses exactly what the Scriptures say. Point by point, he demonstrates how Ware and Grudem depart from it. They argue that the Father and Son are differentiated in authority; no, says the Creed. They reject the doctrine of the 'eternal generation of the Son' – the "foundational element in the doctrine of the Trinity". (This is the orthodox view that the Father eternally begets the Son, and the Son is begotten of the Father.) They deny, contrary to the Creed, that the Father and the Son are one being, homoousios in Greek.

In Giles' view, Grudem and Ware are promoting doctrines that are false, and dangerously so. His conclusion is: "To be faithful to our doctrinal statement we ETS members we must reject what Dr Grudem and Dr Ware teach on the Trinity."

His postscript, however, is most interesting. After he had finished his lecture, he says, Bruce Ware spoke and announced he had changed his mind about the eternal generation of the Son because "he now recognises it has good biblical support". Giles comments: "He did not mention me but as I am the only evangelical who has written a book on the doctrine of the eternal generation I take it he was saying I had convinced him that he had been in error and needed to say sorry to the evangelical community for leading it reject the foundational element in the doctrine of the Trinity."

Grudem, too, announced he had changed his mind about eternal generation. "He too began by saying that he now believed the doctrine of the eternal generation of the Son and that he would be correcting his Systematic Theology when he revised it!!!"

However, both of them said they still believed the Son was eternally subordinate to the Father, a view clearly contradictory to the historic understanding of the Church. Giles concludes: "I follow what is said in Philippians 2:4-1; in eternity the Son is 'equal' to the Father in all things, in becoming man he took the 'form of a servant' and became obedient to the Father to win our salvation. In eternity he is not a servant/slave. He rules as Lord and King."

Giles' lecture is a masterclass in Trinitarian theology. It also represents a determined push-back, in a highly significant evangelical forum, against what is increasingly being seen as an alarming departure from historic Christian teaching by evangelical scholars who are instrumental in forming the theological outlook of new generations of pastors and teachers. Grudem and Ware have grounded their complementarian view of men and women on a radical revision of the doctrine of the Trinity. On the evidence presented by Giles, it doesn't work.

As he also says in his postscript: "I thought to myself, how long will it be before these two hugely influential evangelical theologians will confess that teaching the three divine persons are hierarchically ordered is also mistaken and a threat to the historic faith."

Follow Mark Woods on Twitter: @RevMarkWoods