The permanence of marriage is symbolised by the life of the child who embodies it. But if marriage includes the choice of a relationship which has no intrinsic connection with procreation, why should it not also include the choice of a time-limited relationship? The costs for children are unlikely to prevail against the trump card of autonomy. Again, this is not a fanciful suggestion. Other societies have known forms of fixed-term bonding, and campaigns are now under way in countries which have accepted same-sex marriage to render this element a matter of choice also.
The sexual dimension of marriage will be undermined In law, marriage is a sexual relationship. Incapacity and wilful refusal to consummate a marriage are grounds for annulment, and adultery is one of the five facts which demonstrate irretrievable breakdown. While in theory one could imagine courts trying to identify same-sex analogies, in practice the law will have to draw a veil over the sexual dimension of the relationship, subjecting disputes to the broad test of 'unreasonable behaviour'. The Civil Partnership Act 2004 certainly does not attempt to fix the sexual dimension of a same-sex partnership, which is thus treated as a matter of choice and agreement. A close same-sex companionship need not be sexually active, so marriage and sex will be similarly disconnected.
Given that civil partnership need not be a sexually-active relationship, the refusal to allow close relatives to enter into that status is illogical. Of course, the state has an interest in preventing children being born of incestuous unions, but this is already covered by the criminal law of sexual offences. It should have no further interest in preventing formal companionships between unmarried family members. Marriage will become like civil partnership in this respect, taking on the same illogicality. If marriage includes relationships which are not necessarily sexual, the companionship of any adults who aspire to formal recognition and its other advantages could be called a marriage.
The moral weight of marriage will be undermined As indicated at the start of this paper, we cannot expect political debate in a plural democracy to rely solely on theological arguments. However, marriage as currently defined derives at least part of its social significance from its historic location in Christian theology. Only in the last generation or so has the Church of England ceased to play a central role in marriage/divorce law reform. Redefining marriage will disconnect it from this heritage and undermine its moral weight and social significance.
In traditional Christian teaching, God created human beings male and female. In marriage, the two halves of humanity come together to share their life and work, and as procreators of yet more human beings. The insufficiency of the individual points also to human dependency on God, just as the joint capacity to 'procreate' children is testimony to our creation in his image. Furthermore, marriage is a symbol of the mutually loving and dependent relationships between the different persons of the Trinity. It also pictures the relationship between Jesus Christ and his bride, the church. The exclusivity and permanence of marriage represent the faithfulness of the one true God, and our commitment to him. The pleasure of sexual union points to the greater joy of spiritual union with God. Marriage is part of the created order which is capable both of considerable social distortion and also of positive transformation in the light of the deepest theological symbolism. This is why so many Christians take complementarity, exclusivity, permanence and sexuality in marriage so seriously.
It is likely that this intense theological symbolism is a subliminal part of why we all think marriage matters so much. One does not need to share the Christian worldview to accept that the social recognition which the label of marriage currently confers in British society depends to a large extent on this submerged theological memory. But redefining marriage to include same-sex partnerships undercuts that memory, and thus also eventually the social recognition to which movements for various forms of sexual liberation aspire.
The proposal to change the current definition of marriage depends on a sense that the man-woman criterion confers no distinctive social goods and represents an arbitrary limitation. But this is not the case. Marriage affirms the equal value of men and women, and promotes the welfare of children. Moreover, the logic of equal recognition and radical choice means that the boundaries of any new definition will be far more vulnerable. Challenges to its exclusivity, its permanence and even its sexual nature will be unavoidable. Marriage risks becoming any formalised domestic arrangement between any number of people for any length of time. On such a trajectory, marriage will eventually unravel altogether.
Dr. Julian Rivers has contributed regularly to Cambridge Papers for the 20 years of their existence. He has published widely in constitutional law, legal theory, and law and religion studies. He is Professor of Jurisprudence at the University of Bristol Law School, an editor-in-chief of the Oxford Journal of Law and Religion, and a member of the advisory board of the Ecclesiastical Law Journal.
Cambridge Papers is a non-profit making quarterly publication which aims to contribute to debate on contemporary issues. The writing group is an informal association of Christians sharing common convictions and concerns. However, this special issue departs from our normal pattern by engaging with the issue of redefining marriage without any appeal to arguments from biblical theology. This paper, like all our papers, is a contribution made by an individual and not representative of any organisation.
 Government Equalities Office, Equal civil marriage: a consultation, March 2012. Since the law of marriage is a devolved matter, the proposal relates only to England and Wales. On 25 July 2012, the Scottish Government announced its intention to enact similar legislation.
 See A Response to the Government Equalities Office - "Equal Civil Marriage" - from the Church of England (June 2012); Response from the Methodist Church in Britain to the consultation on "equal civil marriage" (June 2012). By contrast, the Response from the Catholic Bishops' Conference of England and Wales to the Government Consultation on "Equal Civil Marriage" (June 2012) relies on a 'common and instinctive understanding of the meaning of marriage shared by people of any religion and none'.
 Whether a majority is still 'Christian' depends on how one phrases the question. In the 2001 National Census, 71.8% stated that they were 'Christian' (Office for National Statistics, Focus on Religion (2004), Table 1). By contrast, the British Social Attitudes Survey records a steady drop from 66% (1983) to 44% (2010) in respondents who regard themselves as 'belonging' to the Christian religion. The 2010 survey was the first in which 50% stated that they 'belonged' to no religion. (NatCen Social Research, British Social Attitudes 28 (2011-12), Table 12.1).
 Jürgen Habermas writes critically of the pressures on religious believers to be 'polyglottal' in a plural democracy ('Religion in the Public Sphere', in European Journal of Philosophy, 14:1, 2006, pp.1-25), but it is hard to envisage practical alternatives.
 One suspects that Hugo Rifkind speaks for many in his view that the only arguments are theological or visceral: 'Eeeeuw is no argument against gay marriage', The Times, 9 March 2012.
 Hyde v Hyde (1865-9) L.R. 1 P. & D. 130. The laws of King Cnut (11th century) stated that no woman could be compelled to marry a man she did not like, or sold for money, and that no Christian man should ever have more wives than one. See R. H. Helmholz,The Oxford History of the Laws of England, Vol. I, OUP, 2004, p.46 and pp.44-51 for the impact of canon law on pre-Christian Anglo-Saxon practice more generally.
 Stephen Cretney, Family Law in the Twentieth Century, OUP, 2003, is the definitive account.
 A minister may refuse to marry certain couples who may otherwise marry by civil ceremony, including divorcees, persons related by a certain degree of affinity and post-operative transsexual people: Matrimonial Causes Act 1965, s. 8; Marriage Act 1949, ss. 5A and 5B.
 In Hall v Bull  2 All E.R. 1017, the Court of Appeal found that the criterion of marriage directly discriminated on grounds of sexual orientation. The case is on appeal to the Supreme Court, which may find indirect discrimination instead.
 Marriage Act 1949, s. 2. In England, Wales and Northern Ireland (but not Scotland) parties under 18 need parental, or equivalent, consent.
 Marriage Act 1949, s. 1.
 National Survey of Sexual Attitudes and Lifestyles II (April 2003): 5.3% men and 9.7% women reported that they were attracted at least once to the same sex, although more often to the opposite sex. Only 0.9% men and 0.2% women reported exclusive attraction to the same sex. The next National Survey is due in April 2013. One recent US study, which draws on several surveys, finds that 11% of adults acknowledge at least some same-sex attraction, 8.2% report having engaged in same-sex sexual behaviour, 1.8% identify as bisexual and 1.7% as lesbian or gay. See Gary J. Gates, 'How many people are lesbian, gay, bisexual and transgender?', The Williams Institute, UCLA, April 2011.
 Note that in law, 'sexual orientation' embraces the entire spectrum of self-awareness and lifestyle: see R (Amicus) v Secretary of State for Trade and Industry  I.C.R. 1176.
 Recent attempts to map the range of sexualities include the Klein Sexual Orientation Grid and the Sell Assessment of Sexual Orientation.
 The Prime Minister has also appealed to stability on a number of occasions, most notably his speech to the Conservative Party conference on 5 October 2011.
 Compare Marriage Act 1949, s. 44 with Civil Partnership Act 2004, s. 2. It would seem that mutual vows are optionally used in civil partnership ceremonies, although no religious service is to be used in a register office or other approved civil premises.
 5.5% of marriages entered into in 2005 had been dissolved by their fourth anniversary, as compared with only 2.5% civil partnerships. ONS, Civil Partnerships Five Years On (Population Trends Nr. 145, Autumn 2011). This may reflect a 'backlog' of stable longstanding informal partnerships. One major Scandinavian study suggests that over time same-sex civil partnerships have higher levels of instability: Andersson, Noack, Seierstad and Weedon-Fekjær, 'The Demographics of Same-Sex Marriages in Norway and Sweden', Demography 43.1, 2006, pp.79-98.
 Gender Recognition Act 2004, s. 4(3)-(4).
 260 gender recognition certificates were issued in the year 2010-2011. In only four cases was an interim certificate issued, because a marriage or civil partnership needed to be dissolved: Ministry of Justice, Gender Recognition Certificate Statistics Bulletin, 29 March 2012.
 Carol Gilligan, In a Different Voice, Harvard University Press, 1982, was a seminal work. See also Robin West, 'Jurisprudence and Gender', University of Chicago Law Rev.55, 1988, pp.1-72.
 Many historic legal consequences of marriage did not reflect gender equality; but it is the core definition which is now at stake.
 Robert Putnam's 'Bowling Alone: America's Declining Social Capital' (1995) is now a classic study.
 Joint adoption for same-sex couples has been available in the UK since 2005; joint registration after fertility treatment since 2009: ONS, Civil Partnerships Five Years On, Population Trends Nr. 145, Autumn 2011, p.19.
 In 2011, 8.5% of civil partners and 4.8% of cohabiting same-sex couples had dependent children, amounting to 0.1% of all dependent children. ONS, Families and Households 2001 to 2011, January 2012, Table 1. Given the relatively recent introduction of adoption and assisted reproduction, these children are likely to be from previous relationships.
 Of numerous studies of the negative impact of divorce, see the older meta-analysis of 92 studies by Paul R. Amato and Bruce Keith: 'Parental Divorce and the Well-being of Children', Psychological Bulletin 110, 1991, pp.26-46. Judith S. Wallerstein and Julia Lewis, 'The long-term impact of divorce on children', Family Court Review, 36, 1998, pp.368-383, present a focused and qualitative study.
 Universal Declaration of Human Rights 1948, art. 1.
 See the American Psychological Association policy statement on Sexual Orientation, Parents and Children (2004): http://www.apa.org/about/policy/parenting.aspx (accessed 30 August 2012).
 A recent issue of Social Science Research contained a debate on this issue. Loren Marks challenged the reliability of the studies underlying the conventional wisdom: 'Gay and Lesbian Parenting: the State of the Science', Social Science Research, 41, 2012, pp.735-751, and Mark Regnerus presented the findings of the largest survey yet conducted: '[The survey] also clearly reveals that children appear most apt to succeed well as adults - on multiple counts and across a variety of domains - when they spend their entire childhood with their married mother and father, and especially when the parents remain married to the present day.' 'How different are the adult children of parents who have same-sex relationships?', Social Science Research, 41, 2012, pp.752-770. Subsequent expert commentators accept that the research has at least put a question mark against the conventional wisdom, but caution generally against using social science research to solve constitutional questions around same-sex marriage.
 See Christiane Olivier, Jocasta's Children: The Imprint of the Mother, Routledge, 1989, and at a more popular level, Robin Skynner and John Cleese, Families and How to Survive Them, Cedar Books, 1993, ch. 5.
 The right of the child to biological parenting is apparent from the UN Convention on the Rights of the Child (1990), articles 7-9, which contain rights to know and be cared for by both parents, to preserve family identity, not to be separated from parents against their will, as well as a right to maintain personal relations and direct contact even if the parents are separated. Article 3 of the UN Declaration on Social and Legal Principles relating to the Protection and Welfare of Children, with special reference to Foster Placement and Adoption Nationally and Internationally (GA Res. 41/85 of 3 Dec. 1986) states that the first priority for a child is to be cared for by his or her own (i.e. biological) parents.
 On this cultural development, see Anthony Giddens, The Transformation of Intimacy: Sexuality, Love and Eroticism in Modern Societies, Polity Press, 1993.
 Matthew Parris expresses this ideal with customary clarity: 'The day that the battle for homosexual equality is won and over will be the day when a man, straight or gay, can boast that he chose.', The Times, 21 April 2012.
 See, e.g., the arguments of Ronald Dworkin in Sovereign Virtue, Harvard University Press, 2000, ch. 14. Dworkin makes clear that he considers 'prohibitions' on same-sex marriage to breach each person's foundational right to ethical independence: Justice for Hedgehogs, Harvard University Press, 2011, p.369.
 Around fifty, mostly Muslim majority, countries recognise polygamous marriages, either generally or for Muslims under their personal law.
 The growing construction of an 'identity' among the small British community of 'polyamorous people' can be seen at http://www.polyamory.org.uk/. The first goal of the (US) Polyamory Society includes 'to support, defend and promote the social institution of polyamory': http://www.polyamorysociety.org/mission.html (both accessed 30 August 2012).
 Philip L. Kilbride, Plural Marriage for our Times: a reinvented option?, Bergin & Garvey, 1994. See also the manifesto, 'Beyond Same-Sex Marriage' athttp://www.beyondmarriage.org/full_statement.html (accessed on 17 September 2012).
 Jean Hannah Edelstein, 'Why shouldn't three people get married?', The Guardian, 6 September 2012.
 Quite apart from the emotional impact, the cost of family breakdown to the public purse must be phenomenal. The obvious methodological caveats notwithstanding, The Relationships Foundation has recently calculated a figure of £41.7bn a year: Counting the Cost of Family Failure (2010).
 E.g. the nikah al-mut'ah of traditional Shi'ite Islamic law.
 'Mexico City considers fixed-term marriage licences', The Guardian, 30 September 2011.
 Matrimonial Causes Act 1973, s. 12(a) and (b); s. 1(2)(a).
 Civil Partnership Act 2004, s. 44, only has 'unreasonable behaviour', separation and desertion as the facts establishing breakdown.
 The European Court of Human Rights upheld this restriction by a majority in Burden v United Kingdom (2008) 47 E.H.R.R. 38, but the logic of the dissenting judgements is impeccable.
 Sexual Offences Act 2003, ss. 64-65.
 Except, of course, a significant financial one. But that begs all the questions.
 On the political role of the Church of England in 1960s divorce reform, see Cretney,Family Law in the Twentieth Century, OUP, 2003, n. 7, ch. 9.
 From the substantial literature see Christopher Ash, Marriage: Sex in the Service of God, IVP, 2005, and Tim and Kathy Keller, The Meaning of Marriage, Hodder & Stoughton, 2011.
 And it is why the Government's proposal also gives rise to more serious unresolved problems of conscientious objection than did civil partnership.
 Grace Davie draws on the works of French sociologists Danièle Hervieu-Léger and Maurice Halbwachs to analyse religion in terms of various forms of collective memory: see Religion in Modern Europe: A Memory Mutates, OUP, 2000.