IN THE Church of England's debates about same-sex marriage, disagreements about homosexuality are not the whole story. Our debates are also shaped by disagreements about gender - and because that has received less attention, I fear we are sleepwalking into some very worrying terrain.

Assumptions about gender often lurk just below the surface of our arguments. Take the recent spat about the House of Bishops' Pastoral Guidance ( News, 21 February; Letters, 21 and 28 February). The Guidance claimed that there will now, "for the first time, be a divergence between the general understanding and definition of marriage in England as enshrined in law and the doctrine of marriage held by the Church of England and reflected in the Canons and the Book of Common Prayer."

The accuracy of this statement was challenged by Linda Woodhead (Professor of Sociology of Religion at Lancaster University), and then by a wider coalition of academics, who pointed to other divergences in marriage's recent legal history.

Why did this fight - obviously in itself no more than a crack leading off from the deeper fissures that afflict the Church - evoke such passion?

ON THE one hand, there were the critics who demanded that the Bishops' Guidance be corrected or qualified. In part, this was no doubt driven by the academic habit of questioning claims such as this - we academics are, after all, professional pedants. But, for at leastsome of the critics, there was clearly more to it. Some of their passion came from the conviction that marriage is a complex historical reality, which has always been evolving and appearing in divergent forms.

When some critics accused the Bishops of historical illiteracy, their real accusation was not that the Bishops had got one fact wrong, but that this was a symptom of a wider failure to take history - and specifically the messiness and complexity of the history of marriage - seriously.

On the other hand, the defenders of the Guidance asked how the critics could make such a fuss about a secondary detail, without realising that it left untouched the obvious point that the Bishops were making. For at least some of the defenders, the central fact of the new legislation on same-sex marriage is that it denies the centrality of the fundamental complementarity of men and women to the definition of marriage.

Questions about remarriage after divorce or about dead wives' sisters (both cited by critics as earlier areas of divergence in the understanding of marriage) are, for them, clearly not in the same league as this question - and neither are broader questions about the complex historical evolution of marriage as an institution. We are, they might say, not dealing with messy historical relativity, but with a fundamental structure of creation.

So this was not simply a tiff about a detail. It was the flick of a seismograph's needle, alerting us to a deep clash of intuitions about the relationship between what some see as "the fundamental complementarity of men and women" and the messy historical evolution of the institutions in which men and women relate.

Deep down, it was all about gender.

OUR tendency not to notice how central questions about gender are to our disagreements about same-sex marriage has led us into some worrying territory. Take the Church's official response to the Government Equalities Office Consultation on "Equal Civil Marriage", from 2012.

The framers of that document rightly noted that their response to the question of same-sex marriage was not directly about homosexuality, but rather had to do with "the fundamental complementarity of men and women" - although very little of the ensuing debate focused on that fact.

Yet the main argument of that 2012 church response runs as follows:

1. There is an essential complementarity between men and women.

2. The acknowledgement and expression of this essential gender complementarity is necessary for the flourishing of human society.

3. Acknowledging and expressing this complementarity is central to the purpose of marriage.

4. Indeed, marriage is the primary social institution by which our society acknowledges and expresses this complementarity.

5. If marriage ceases to be a way for our society to acknowledge and express this complementarity, our society's capacity to acknowledge and express it at all will be seriously reduced, and society as a whole will be harmed.

(This, by the way, is what was meant by the response's claim that the proposals would "change the nature of marriage for everyone". The authors did not think that my marriage would somehow be undermined if other people entered intoa union of which I disapproved. Rather, they thought that marriage as an institution would be less capable of performing one of its most important social functions if it ceased to be defined in gender terms.)

6. The essential complementarity of men and women is biologically grounded, but it is not reducible to capacity for procreation.

7. Properly acknowledged, this complementarity will be expressed in specific and distinctive contributions from men and women in all social institutions.

The report says that marriage is the means by which we recognise and celebrate the essential complementarity of men and women, and that we need to recognise and celebrate that complementarity not just for the sake of marriage, but the sake of our whole society, which will flourish more fully if the distinctive contributions of men and women are given full expression in all its parts.

I FIND it troubling that we as a Church could publicly proclaim that this is our undisputed theology of gender, without qualification or cautionary gloss.

If you cannot see why I am troubled, ask yourself what would happen if we were to declare that we now need complementary accounts of the ministry of male bishops and female bishops, or male priests and female priests. Imagine, that is, that we were to insist that there is male ministry and there is female ministry, and that they are fundamentally different, even if equal in dignity - and that we stand against any account of ministry that refuses to distinguish the genders in this way. Think of the controversy that would erupt.

Suppose, for a moment, that we had heard that the Church was putting together a commission to write a report on "Gender in Church and Society". (I am not saying that this would be a good idea; I am pretty sure that the world does not need another church report in this area.)

Suppose that this commission were asked to clarify the Church's understanding of the nature of gender - how our understanding should be shaped by our reading of scripture, our engagement with tradition, our attention to biology and to experience, and by our listening to the many other accounts of gender alive in our society.

Think of the agenda such a commission would need to tackle, if its work were to be taken seriously. It would need to ask what it means to repent of the Church's toxic collusion in patterns of sexism over the centuries, and right up to the present day. It would need to explore the roles that the Church can and should play in fighting for gender justice.

It would need to look at what we have said, and what we should say, about the ministry of women and men at all levels in the Church. It would need to think through what happens to our accounts of gender when we set them fully in the context of our account of the gospel, and of the Spirit's work in and through our desires.

MY FEAR is that, because our attention has been elsewhere, we as a Church have not been engaging in such deliberation together, before stating our position on gender. We have therefore been sleepwalking into a minefield. And now that we are here, we urgently need to wake up, to look about us, and to start treading much more carefully. The consequences if we do not could be messy.

Taking these questions more seriously will not lead to agreement, of course. Rich and careful thinking about gender can be found in all sorts of places in and beyond the Church, and serious attention to those varied voices certainly will not push us in a single direction. It will teach us that we do not have to choose between a blunt "complementarianism" (like that of the Consultation Response on same-sex marriage) and an equally blunt individualism that ignores sexual difference - because these are not our only options.

It will teach us that we have not inherited any simple consensus about gender from the Christian tradition. And it will teach us, above all, that these are genuinely complex matters that require nuanced, cautious, and pastorally sensitive responses. But it will not lead us to agreement even about the nature of gender and of gender justice, let alone about same-sex marriage or homosexuality.

I do not have my sights set on consensus, however. I would settle for our learning to do more justice to each other's arguments, more justice to the richness of the scriptures and the tradition, and more justice to the complexities of our biology and our experience. When I see what we have been saying about gender, I do not want us to disagree less - I want us to disagree better.

Mike Higton is Professor of Theology and Ministry at Durham University.