It is not often that an open letter to a bishop is published in a truly irenic spirit. I had known for some time that the late Canon Roger Greenacre had wanted to write such a letter to me because of our disagreement over the ordination of women, in spite of our common cause in working for Christian unity. After the General Synod's decision on women bishops, his hesitation and my response are topical.

Traditionalist Anglicans have emphasised the need for continuity with the past and conformity with Rome and the Orthodox. Roger developed his argument by reference to the Patristic tradition and its central significance for development of Anglicanism. My response to Roger affirms that the ordination of women to all three orders of ministry is an authentic development of the classical Anglican tradition.

Dr Colin Podmore, a friend in common and Roger's literary executor, has edited a number of Roger's papers, the first of which is his unfinished and unsent open letter (Part of the One Church?: The ordination of women and Anglican identity, Canterbury Press, 2014). Although addressed to me as an old friend and ecumenical colleague, it is really a contribution to the painful debate between Anglicans of the Catholic tradition who differ over the ordination of women.

Nevertheless, as Dr Podmore acutely observes in his introduction: "The open letter . . . was . . . to a significant degree, directed not to its addressee or to its wider audience, but to Roger himself."

This is not just an argument about the figures on whom we focus - Vincent of Lérins and John Henry Newman - two dead theologians of the fifth and 19th centuries respectively. It is an argument about continuity and change in the Church today. How do we judge what is good in the new, and how do we discern what is fake? Both Vincent and Newman lived at times of profound change, and are highly relevant to the 21st-century Church.

Central to Roger's argument is his understanding of classical Anglicanism, which accused - to use the less than ecumenical language of the day - both "Papists" and "Puritans" of innovation; Roman Catholics adding, the Reformed subtracting from the "faith once delivered to the saints". Roger considered these two theologians from different epochs because of the way they wrestled with the inescapable question of innovation in the life of the Church.

My response to Roger looks especially at Vincent. His famous canon, or rule, was itself the starting point for Newman's Essay on the Development of Doctrine. Vincent was special to Roger. He once sent me a postcard of his beautiful church in Beaulieu-sur-Mer, close to which are the islands of Lérins, where Vincent's community lived and prayed, and where he wrote his Pilgrim against the Heretics.

Note the word "pilgrim", which can also be translated as "journeyman". The great German Protestant Church historian Adolf Harnack speaks of Vincent's work as bringing fresh air and light into the question of tradition.

But the rule, or Vincentian Canon, for which he is famous has to be understood imaginatively. Roger quotes it as central in the classical Anglican appeal to "what is always, everywhere, and by all believed".

He notes that Vincent went on to sketch an early version of a doctrine of development, and Newman, especially in the second edition of his Development, explores this. But the firstrule - accept only what has been always, everywhere, and by all believed - is what most people remember.

That rule was central to classical Anglican apologetic and the wider Reformation and Counter Reformation debates. No less than 35 editions of Vincent's work were published in the 16th century. Understood as a kind of fossilised tradition, the Vincentian Canon might seem to rule out the ordination of women. But it need not be read in this way.

Applied rigidly, it can be argued that nothinghas ever been found always, everywhere, and by all. Distinguished theologians as diverse as Yves Congar, Joseph Ratzinger, and Karl Barth have in different ways rejected the utility of Vincent's rule. But contemporary interpreters of Vincent - and I acknowledge a debt to Thomas Guarino, in his Vincent of Lérins and the Development of Christian Doctrine (Baker Academic, 2013) - deny that his argument is either impossibly idealistic or antiquarian.

We need to look at Vincent's "always", which Roger highlights. It cannot mean fossilised antiquity, because Vincent also expounds a doctrine of development as his second rule. While he certainly uses language of preservation, he also uses the metaphor of organic growth, later used by Newman. He also sets out multiple criteria or tests for authentic development.

Vincent starts with scripture as determinative, but if scripture is not decisive (or more often quoted by heretics), then next come councils. He was utterly committed to the Council of Nicaea, which took place about a century before him. But the "always" also included the very recent Council of Ephesus of 431.

Both councils introduced new teaching and non-scriptural language, yet with the intentionof preserving the true meaning of the incarnation. So Vincent's "always" is subtle. After creeds come bishops (the Bishop of Rome is given a special place) and also theological teachers, and the emergent mind of the laity.

All these criteria are relevant. Other than scripture, no one criterion trumps the others. The way Vincent that uses the intention of the councils is important: innovation with the intention of true continuity. For Anglicans, the ordination of women is in intended continuity with apostolic faith and order, and not otherwise. 

My irenic reply to Roger would be to welcome a positive engagement with Vincent of Lérins. His exploration of development can be regulative, without being static; open to development, without "mummification" of tradition.

If we explore Vincent's criteria for organic development (scripture, councils, bishops, teachers, the lay voice), and the ordination of women, we find that scripture is not explicit or decisive (as the Pontifical Biblical Commission pointed out many years ago); there are no formal conciliar judgements against, and the nearest Anglican equivalent, in the Lambeth Conferences, have deemed the question a matter for each province.

Bishops in a divided Church universal do not give a clear verdict, and Anglican bishops - again the Lambeth Conferences - are generally in favour, although the Bishop of Rome, through the Congregation for the Doctrine of the Faith (CDF) and Benedict XVI, has spoken against it.

Yet even here, Congar believed it significant that the definitive CDF statement fell short of claiming that its teaching was of "divine right". Moreover, theological teachers - Anglican, Protestant, and many Roman Catholics - weigh in favour. The view of the laity is clearly favourable in places where women's ministry is culturally acceptable.

I would therefore argue that, in a divided Church, while it is less easy to test the authenticity of development than even in Vincent's day (and it was not easy then, which is why he wrote his book), the ordination of women must be open for provincial implementation.

Roger was not an "impossiblist". He was really questioning provincial autonomy in this matter. Elsewhere in his writings, he cites approvingly an earlier statement of mine to the effect that provincial autonomy, understood as independence, is one of the "hair-line faults" of the Reformation. This is a view that Archbishop John Habgood concurred with.

In an ecumenically divided Church, however, there are fault-lines in all the Churches. Before their resolution, and towards our reconciliation, Vincent's exploration of development - and Newman's - is still a good starting point for An-glican debate.

While the universal ecumenical reception of the ordination of women is still to come (as the third principle which the Bishops included in their declaration decision, and which is now part of the women-bishops package, states), Anglicans should both welcome the Synod's decision and the continuing place (as in the Bishops' fourth principle) of those who read Vincent differently from me. But it is my conviction that Vincent's criteria for development, taken as a whole as he intended, point positively, not negatively. 

Dr Christopher Hill is the Presidentof the Conference of European Churches, and a former Bishop of Guildford.