“PLAN B”, a guidebook for unmarried women living in Seoul, the South Korean capital, begins with a test. “Have your parents chided you for wanting to live alone?” “Are you often told that a woman’s best chance of happiness is being a wife and mother?” Too many noes will land the reader in the “soft tofu” category—unprepared for the rigours of life as a single woman in socially conservative South Korea. (Other types include thick-skinned “watermelon” and die-hard “walnut”.)

The guide, put together last year by the Seoul metropolitan government and the Unni Network, a women’s organisation, and distributed in 600 offices and public places, offers tips for staying safe, good reads on living solo and information on dining clubs for young singles. The proportion of single people in Seoul more than doubled between 1990 and 2010, and they now account for 16% of households. Four in ten South Korean adults are unmarried, the highest share among the 34 OECD countries. In Seoul over a third of women with degrees are single.

One reason is that wedding expenses, mostly met by the groom and often including the couple’s first home, have become prohibitive for many. Another is that Korean families used to be so desperate to have sons that in the 1980s they aborted lots of daughters. Now one in seven men of marriageable age lacks a potential partner.

Also, some women want to “marry up”, which is harder now that so many women have degrees and good jobs. Many others are no longer prepared to play the role of a traditional wife. The mean age at which women marry has risen from 25 in 1995 to 30 today.

Social expectations have yet to catch up. The Unni Network wants to popularise the neutral term bihon (single) over mihon (not yet married). It has held public bihonshik, ceremonies for women who choose not to wed and vow to live happily as singles. Some studios are offering “single weddings”: photo shoots for unmarried women in bridal gowns. Park Hong-joon, who owns a photo agency in Seoul, has heard wedding guests say they wanted their special-day snaps to be taken in their prime. He now offers dresses and stylists as part of a single-wedding package.

Clients sometimes invite friends to join the photo shoot. Quite a few are unmarried women in their late 30s and 40s who want portraits for their homes. Some hope to add a husband later. Others want to celebrate their solo status, says Mr Park. In Japan, where the idea arose, an agency offers male models as grooms, but no women there have opted for the service.

Men have poured scorn on single weddings, says Mr Park, calling the concept “absurd”. Some snipe that these women’s “marriage strike” is selfish and unpatriotic, by which they mean that they would like women to carry on shouldering nearly all the burden of housework, child care and looking after ageing in-laws. Even otherwise modern-minded online men’s clubs, such as “I Love Soccer”, have taken to deriding feminists and calling women’s forums childish. Birth rates in most rich countries have plummeted in recent decades (see article)—but further and faster in South Korea than almost anywhere else.

Successive governments have regarded the promotion of traditional marriage as a way to boost procreation, says Kwonkim Hyun-young, a lecturer in gender studies at Sungkonghoe University in Seoul. This does not seem to work. Granted, the stigma against cohabitation remains strong: only 0.2% of Korean households consist of unwed couples, compared with 10% in Britain and 19% in Sweden. But rather than getting hitched, many women remain single. And many married couples are having only one child: the number of children beyond a first fell by 37% between 2010 and 2013. So long as South Korean wives and mothers are expected to behave like their mothers did in the 1960s, many women will opt to fly solo instead.