The culture and laws behind the choice for family names

When my wife and I filed for our marriage certificate in 2002, the civil office clerk asked her if she wanted to keep her family name or take mine. We exchanged a second-long glance and then she ticked under my surname.

Earlier that day, she had jokingly tested my ego by asking if I minded her keeping her father’s name. Instead of giving her a straight answer, I asked back whether she had a liked or not my family name. The choice felt easy, almost automatic, though deep inside I felt it wasn’t truly a free choice.

My country does not oblige legally registered couples to assume a single name for all members. Wives are allowed to keep theirs or create a double-barreled family name. Husbands have the same legal right, though no one usually asks what they truly desire.

Most men, if pressed, admit they want to pass their bloodline to future generations through their surnames. I am sure many women would want exactly the same thing, if asked the same question.

But in practice, in many countries one of them is expected to compromise.

This is not merely a matter of tradition or ego. One surname for all family members serves many practical functions: streamlined government records, simplified household registration, reduced fraud risk, smoother travel and border control, faster medical emergency responses, easier school verification, clearer inheritance tracking, and — to name a decidedly less noble concern — the prevention of awkward confusion when someone tries to determine if someone is in an official relation and therefore should be avoided for dating.

These are real benefits. To dismiss them would be dishonest.

But the fact that a system is convenient for the state — or even convenient for families on a day-to-day basis — does not automatically make it just for the citizen. Convenience and justice are not the same thing. And when a society elevates administrative efficiency over individual identity, it makes a choice. Not a necessity. A choice.

Nowhere is this (lack of) choice more visible, or more mathematically unsettling, than in Japan.

The hidden risk of homogeneity

Before we examine Japan’s specific situation, let me ask a broader question: what is actually lost when family names converge?

Homogeneity in anything — genetics, culture, language, or surnames — carries inherent risks. The most obvious is the loss of information. A diverse set of surnames encodes centuries of migration, marriage, class, geography, and occupation. Each name is a tiny archive. When names vanish, those archives close permanently.

Consider what a surname can tell you at a glance: regional origin (Sicilian vs. Venetian names in Italy), ancestral trade (Smith, Taylor, Cooper, Carpenter), religious or ethnic heritage (Cohen, O’Brien, Kowalski), or even political history (many Vietnamese names date only to the Nguyen dynasty’s forced standardization).

A world of identical surnames would be a world without these quiet stories.

Beyond information loss, homogeneity creates vulnerability. In a hypothetical Japan where nearly everyone is named Sato, what happens to individual privacy? What happens to credit reporting, criminal background checks, or medical record matching when a query for “Sato, Tokyo” returns millions of citizens?

The very administrative efficiency that single-surname laws promise begins to collapse under its own success. Diversity is not just cultural; it is functional.

Finally, homogeneity signals compression of social freedom. When 96% of couples follow the same naming pattern — mostly the man’s name — not because a law explicitly demands it but because custom and pressure make alternatives unthinkable, the result is indistinguishable from coercion. A choice that no one feels free to make is not a choice.

Japan offers a stark, data-driven example of where this path leads.

The Sato simulation: A mathematical warning

A study published by the Tohoku University’s Research Center for Aging Economy and Society suggests that all Japanese will have the same family name by 2531 — Sato — which is the most popular in this Asian country.

Japan currently requires couples to choose between their family names when they get married and 96% prefer the man’s name.

In 2023, as many as 1.5% of the Japanese population were called “Sato” — which does not seem impressive — but mind that during one year only the adoption rate for it was 1.0083 times.

The root of the problem is the marriage law, adopted in the 1800s, which makes it compulsory for couples to choose one name for all members of the family. If this legal condition remains and the adoption rate maintains, everyone will be called Sato by 2531, the researcher said, noting that this is “just a probability,” according to a simulation run at this institution.

If, however, Japan amends the marriage law to allow for separate names, only 7.96% of Japan residents citizens will become Sato within the next 500 years. Under such scenario, Sato would conquer Japan not earlier than by 3310.

According to the National Institute of Population and Social Security Research (IPSS), Japan’s population is projected to decline from approximately 125 million in 2020 to 41 million by 2120 under the medium-fertility scenario.

Professor Hiroshi Yoshida of Tohoku University, the author of the study, extends these projections further, suggesting that by 3310 — under continued low fertility — the population could fall to as low as 22 million.

“In other words, even if 100% adoption of the Sato name is postponed for 800 years, there is a high possibility that the Japanese people themselves will become extinct before that due to the declining birthrate,” Professor Yoshida claims.

Paradoxically, the same demographic decline that drives the simulation’s math in Japan also threatens to overtake it. Extinction, not homogeneity, may be the more immediate risk.

Customs and laws in other countries

Before we conclude that Japan’s predicament is unique — or that its marriage law is the only sensible way to organize a society — it is worth looking at what the rest of the world actually does. The answer is surprising, and it defies easy generalization.

Some countries have chosen the opposite extreme from Japan. In Quebec, Canada, provincial law has forbidden a woman from taking her husband’s surname since 1981. The rule was enacted following the Quebec Charter of Rights, which took effect in 1976, and is intended to extend the charter’s statement on gender equality to names.

A woman in Quebec who wants to be known by her husband’s surname cannot do so on any official document.

Greece enacted a similar law in 1983 during a wave of feminist legislation, requiring all married women to keep their maiden names.

France has since 1789 had a law requiring that citizens use only the name given on their birth certificate. Today, French women cannot legally change their surname after marriage, though both men and women may accept the other’s surname for social and colloquial purposes.

Italian women have more options. Although they cannot legally change their surname, which has been true since 1975, they have the option of adding their husband’s surname next to theirs.

Women in the Netherlands are identified in documents by their maiden name and can take their husband’s name under special circumstances only. Belgian law prohibits the change of one’s surname after marriage.

In Malaysia and Korea, it is local custom for women to keep their maiden names, and although there is no law stating that they cannot take their husband’s surname, it is a relatively foreign concept. Custom dictates that women keep their surnames in many Spanish-speaking countries as well, including Spain and Chile.

In the U.S. women are increasingly keeping their maiden names.

In Romania, the system is even more generous as couples have all options on the table:

• Both spouses keep the names they had before marriage (each retains their original surname);
• Both spouses take the same surname — either the surname of one of them or a combined surname formed by joining both names;
• One spouse keeps their pre-marriage name, while the other takes the combined surname (the reunion of both names).

There’s more. A spouse who wanted to keep the married name needed the former partner’s consent or a court decision in Romania. A new amendment awaiting promulgation eliminates this requirement — each former spouse can now keep the name acquired during marriage without the other’s permission.

What does this global tour tell us?

It tells us that Japan’s law is not natural, inevitable, or universal. It is a choice — one choice among many. Quebec, Greece and France chose to forbid name changes entirely. Italy chose a hybrid model. Malaysia and Korea chose custom over law. The United States is choosing, slowly and unevenly, to let women keep their names.

Romania, by any measure, is a total libertine. Its example shows that even in a country that already allows choice, the law continues to evolve toward greater individual autonomy over one’s name. The trend, globally, is away from spousal control and toward personal freedom.

Not one of these societies has collapsed. Not one has lost the ability to identify families, process taxes, or run companies. The supposed administrative necessity of a single surname turns out to be, on closer inspection, a convenience — and one that many countries have decided is not worth the price.

In Japan’s case, the price is the slow, mathematically predictable extinction of nearly all family names except one. By 2531, if nothing changes, Sato wins. Not because it is a better name. Or because the Japanese people voted for it. But because a 200-year-old law, combined with a 96% social preference for the husband’s name, creates an inexorable arithmetic.

However, Professor Yoshida’s simulation is not a prophecy. It is a warning. And warnings, unlike prophecies, can be heeded.

The fact that Romania allows couples to keep separate names without social collapse or bureaucratic chaos undermines the argument that Japan’s law is necessary for family unity or administrative order.

One may argue that bias toward male spouses was almost omnipresent in European marriage laws during medieval times, and yet surname diversity has never been greater in Europe today. This seems to contradict the Japanese simulation.

But the difference lies in what Europe had that Japan lacks: linguistic fragmentation, patronymic naming traditions that changed every generation, and a much deeper, more diverse pool of surnames to begin with.

The Japanese case is not the inevitable outcome of male bias. It is the outcome of male bias combined with a specific set of legal and demographic conditions that Europe never experienced all at once.

The state exists to serve families, not the other way around. A law that elevates administrative efficiency over individual identity has forgotten its purpose.

So, before hitting the publish button for this opinion piece, I asked my wife again:

“Would you like to reverse to your maiden surname now?”

“No, I am fine. And frankly, it doesn’t really matter. It’s not the surname that holds a family together.”