This evening, in New Zealand, the 120 members of Parliament will vote on same-sex marriage. Professor Rex Ahdar, of the University of Otago, published this cogent defence of traditional marriage in the New Zealand Herald yesterday.  "Give us equality" ... "don't discriminate" ... These are catchcries of proponents of same-sex marriage. Gay couples assert the right to equal treatment and to deny them legal marriage is, they say, blatant discrimination.
This assertion deflects attention from the real issue: what is the true nature of marriage? Two visions of marriage confront us. The conjugal model says that marriage is a lifelong union between a man and a woman. The partnership model says marriage is a contract between committed, loving couples.
So what is marriage? Conjugal marriage is a comprehensive union (mental and physical, emotional and sexual) of a man and a woman. It has a true essence, a fundamental nature; it is a real phenomenon, not just a human invention or convention. A hedgehog is a hedgehog, a tree is a tree, a river is a river. We did not invent hedgehogs, we simply named them. We can call a cat a hedgehog if we want but that does not change its essential nature. All it does is lead to confusion.
Marriage is a pre-political institution, a social solution that pre-dates governments. States recognise marriage; they do not invent it. Marriage is a valued institution because it channels the natural impulses between men and women in a socially beneficial direction. Men and women commit indefinitely and exclusively to each other and to the children their sexual union commonly (but not invariably) produces. It is a stable institution that provides for the rearing of the next generation.
Gay marriage advocates will reply: you have just defined marriage so as to exclude gay couples, a neat trick that fools no one.
Not so. Recall the key claim: gay couples deserve equal respect and legal recognition by the state.
But arguments based on equality are empty. To insist upon equality is to require that "like things are treated alike". So X and Y should be treated equally for X and Y are alike. But we need to know in what respects X is like Y and whether these characteristics are valid before we can be confident that they merit equal treatment. We must have a rule or standard for deciding which characteristics count and which don't. Statements of equality are mere conclusions that logically derive from the prior application of a standard.
Is gay (partnership) marriage "like" conjugal marriage? In some respects, yes: both may involve monogamous couples who may have a deep, lifelong commitment to each other. Both can express this caring commitment in a sexual fashion; raise children (if any) in a thoughtful, caring way. In other respects, however, the answer is no: lacking sexual complementarity, gay couples cannot achieve complete sexual bodily union. And lacking reproductive capability they cannot be biological parents.
They can provide love but they cannot provide the example that a father and a mother can. They lack the inherent structure to rear well-rounded, psychologically secure children. A parent of each sex is needed to raise and teach a child, because the child needs a model of his or her own sex, a model of the other, and a model of the relationship between them.
Some may gasp: how antiquated! Who says these attributes - sexual complementarity, reproductive capacity - are essential? Who says this is the standard? We did. We long ago recognised that marriage involves the comprehensive sexual union of a man and a woman. By contrast, common race, religion and class are not essential. We discerned that, ideally, children are best raised by their biological father and mother. (This is not, of course, to demean the valiant efforts of single parents, or step, adoptive and foster-parents that successfully raise children, but merely to affirm that both biological parents are, as empirical research attests, the optimal configuration).
By "we" I mean virtually every culture, tribe and race since antiquity has affirmed these as essential elements of this thing called marriage and accorded such unions special status. It might be that nearly every society through the ages (with a few short-lived exceptions) has got it wrong and we alone in the West have now stumbled upon the truth. But I think not.
The use of the slogan "equality" cleverly skews the debate. Brazenly repeat that conjugal marriage and partnership marriage are equal (as if this were somehow self-evident). Repeat that principled differentiation is the same as egregious discrimination. The onus then shifts on those who would deny this to show why "unequal", "discriminatory" treatment is justified. And who can be against "equality" or defend "discrimination"? Opponents must show why this enlightened humanitarian proposal is wrong, rather than the gay marriage proponents having to demonstrate why the new model deserves to replace the existing institution.
And make no mistake. To redefine marriage (to allow same-sex partners) is to abolish it. Partnership marriage does not keep the existing institution and simply allow more persons to join it. No, it eviscerates it and substitutes a new concept. Such a redefinition, while internationally fashionable, would, I suggest, be a radical unwarranted move and would begin a social experiment the long-term results of which are wholly uncertain. Professor Rex Ahdar is from the Faculty of Law, University of Otago, New Zealand. His article has been republished with permission.