Jill Kirby: The benefits of marriage are not coincidental

As hundreds of guests arrive at the Abbey this morning, thousands of spectators line the streets of Westminster and millions of viewers tune in on TV or Youtube, Prince William and Catherine Middleton will be aware that the promises they make to each other are being witnessed by more people than at any previous wedding in Britain (and probably the world). This must be terrifying for the couple: wedding nerves multiplied to an unimaginable extent. But to offset those nerves, what an extraordinary sense of confidence the bride and groom will have from the knowledge that millions of people are wishing them well, sharing their day and wanting this marriage to succeed.

No other married couple can count on goodwill on this scale. But every couple deciding to get married is making a public statement as well as a private commitment. Set aside for one moment the grandeur of today's ceremony, its constitutional implications and the media circus. Think about any couple of your acquaintance, and ask yourself how your attitude is changed by their decision to marry and to make their promises to each other in front of you, their family and their friends - whether in a church, a registry office, a stately home or hotel garden. Marriage does make a difference: these two people are telling you that they plan to spend their lives together and that they would like you to help them to stick with that decision. They are no longer just two people who started with a date and ended up living under the same roof.

It should be no surprise, then, that marriage is so much more durable than cohabitation. Getting married requires a decision and a commitment. Most cohabitations just happen. “Sliding, not deciding” is how one marriage expert puts it. And having committed, partners to a marriage seem to find the presence of that commitment helps them through periods of stress or uncertainty, and enables them to better survive big changes in their lives. For example (and perhaps surprisingly) cohabiting couples who have children together are more likely to split up than if they remain childless. Having children together does not put a seal on a relationship. Cohabiting parents are between 3 and 5 times more likely to separate than married parents. Being married before you have children makes you much more likely to cope with the shock of parenthood. In the less likely event that married parents do break up, marriage even offers some protection to children post-divorce: they are much more likely than children of never-married parents to retain contact with the absent parent after separation.

Sceptics maintain that these benefits are not conferred by the institution of marriage but are simply coincidental. They argue that people who get married are more likely to be the responsible, committed types who would have stayed together anyway, and hence there is no point in creating incentives for marriage. But this argument doesn't stack up with the evidence. Nor has the decline in marriage rates over the last thirty years been accompanied by a fundamental change in human nature. The majority of teenagers and young people still claim that they want to get married one day. The extraordinary level of interest in today's royal wedding demonstrates a powerful public appetite not just for ceremony and glamour but for the ideal of lifelong commitment. Policymakers should now be harnessing that idealism by supporting and promoting this most enduring and important institution. Not only does marriage help to shape society, it shapes the lives of those who enter into it.