BRITAIN is nearly there; America not far behind; France passed the milestone in 2007. As couples wait longer to marry, and fewer eventually do, the number of countries where more births are out of wedlock than in it has risen to more than 20. Rates across the OECD group of 34 mostly rich countries vary hugely, from 2% in Japan to 70% in Chile. But overall the average is 39%—more than five times what it was in 1970 (see charts).

Policymakers wish they could change the trend. Unmarried parents are more likely to split up. Their children learn less in school and are more likely to be unhealthy or behave badly. It is hard to say how much of this difference is due to marriage itself, however, because unmarried parents differ a great deal from married ones. They are poorer, less well-educated and more likely to be teenagers, for example.

But efforts to persuade people who otherwise would not marry to do so have generally failed. Isabel Sawhill of the Brookings Institution, a think-tank, says that a plethora of policies in America, from tweaking incentives in the benefits system to teaching couples how to be better domestic partners, have had little or no effect on marriage rates. Better, she says, help women to avoid unplanned pregnancies and delay childbearing at least until they finish school and are in a solid relationship, whether married or not.

Governments must still decide what to do when cohabiting couples break up or one partner dies. They tend to take one of three approaches: to treat unmarried couples like married ones if they have been together more than a couple of years; to treat them as if they were single; or to offer several formal alternatives to marriage and hope that couples will choose the one that suits them best.

Subscribers to the first approach include Australia, New Zealand, Sweden and some Canadian provinces. For legal purposes, cohabiting couples are almost indistinguishable from married ones after some time living together, usually two or three years. De facto marriage may kick in earlier for parents. Some countries allow couples to opt out of some of the provisions of de facto marriage by signing a contract, for example if one partner wishes to exclude property, or money for offspring from a previous relationship.

In Australia, however, couples rarely draw up opt-outs, says Belinda Fehlberg of the University of Melbourne. So courts still end up dealing with messy separations. One party may dispute the very existence of a relationship. In a property dispute in 2013 a judge ruled that a couple who had lived together for 14 years, holidayed together and had regular sex were not in a de facto marriage. The woman claimed they had been. The man, who had married someone else, said they hadn’t, because one had always paid rent to the other.

In Brazil, where two-thirds of children are born to unmarried parents, couples whose relationship is “public, permanent and intended to form a family unit” are regarded as being in a “stable union”. They need not live together, and there is no set period before the law kicks in. Foreign clients find this startling, says Carolina Ducci of Mattos Filho Advogados, a São Paulo law firm; she advises those in unmarried relationships to declare a stable union in a notary’s office in case doubts arise. For those with the opposite concern—that a casual fling might demand alimony—there is no such quick fix. Some rich Brazilians insist on “dating contracts” at the start of any new relationship, says Ms Ducci—but these have no legal status.

Marriages of inconvenience

Such disputes are surprisingly rare, though, because Brazilians know the risks. Anyone determined not to enter a stable union will do nothing that a judge might take as evidence of one. Pictures together on Facebook show that a relationship was public, for example. Paying bills jointly, sharing a bank account or making loan repayments for a partner can be taken as intent to form a family. More common are legal battles after one partner dies: children from a former marriage, who lose out if their parent enters a new union, may dispute that a partner was a de facto spouse.

By comparison, recognising only formal marriage has the merit of clarity. But countries that take this approach, such as many American states, England, Italy and much of eastern Europe, have problems, too. The assumption that all those who want the rights and obligations of marriage will wed is often wrong. In many countries lots of unmarried couples mistakenly believe that they have all the rights of married ones after they have lived together for some time (see article). And often, says Robert Wintemute of King’s College London, one partner wants to marry but the other does not. The reluctant party is usually the richer one, most often the man.

Some people in this situation will leave and look for a less marriage-shy partner; others realise their predicament only after children are born, when keeping the family together trumps unshared marital aspirations. They risk poverty, even homelessness, if they are bereaved or the relationship comes to a bitter end. After a divorce, the parent who does most of the child care usually gets the family home, no matter whose name it is in or who paid for it; without marriage there is no such guarantee.

In England, bereaved unmarried partners may have to sell the family home to pay inheritance tax that a spouse would have been exempt from—if they are lucky enough to be left it, that is. Without a will, they may be made homeless by blood relatives favoured by the intestacy rules. The British government has done nothing to change these, despite recommendations from the parliamentary law commission and family lawyers’ association that some unmarried partners be given the inheritance rights of spouses.

Belgium, France and the Netherlands take a third approach, offering a range of formal options short of marriage. A cohabitation agreement, one of the options in the Netherlands, can be drawn up by a notary; more than half of unmarried Dutch couples had one in 2008. Couples can tailor these with details on how assets and expenses will be shared. A popular choice in France is the pacte civil de solidarité (PACS), which confers many of marriage’s rights and duties but is easier to end: one partner can terminate it by a registered letter or by marrying someone else, without giving notice to the (possibly surprised) ex. Couples in a PACS get the same income- and inheritance-tax breaks as married ones. But if they separate neither can claim alimony or the other’s property. About two-thirds as many French couples are in a PACS as are married—a popularity that has spawned a new verb: se pacser (to “get pacs-ed”).

But even when several options are on offer, many couples choose none. A fifth of French and Dutch cohabiting couples are in no form of registered partnership—the same share as in England, where marriage is the only option. (English same-sex couples can also enter into a civil union, a remnant of the equal-but-separate era before gay marriage became legal in 2014.) In the end governments face a trade-off. Treating long-lasting cohabitation as marriage leads to fewer bereaved and wronged families—but also blurs a once-clear line. Not doing so, though, puts the law out of step with the way families are evolving.