For a decade I have taught American attorneys and law students about the Japanese legal system. One of the great hurdles is getting them to appreciate that, although Japan has a much longer history as a nation than the United States, in many ways Japan’s legal system is actually more modern.

The United States Constitution dates back to the 18th century. and features of the country’s legal system go far back even farther to the roots of English common law. Parts of the Magna Carta of 1215 remain in the United Kingdom’s Constitution. Other similarly ancient laws and institutions—the jury system, for example—are deeply embedded in the legal culture of the United States as well.

By contrast, virtually every law and legal institution in Japan today was created after the Meiji Restoration of 1868. Most can also be traced to what were at the time modern Western (mostly European) models. While the common law system of America and England still contain aspects predating the age of reason, Japanese law and legal institutions were designed by rational people to function as part of a modern system of government.

One example is in how the courts are used in the two countries. Here it is tempting to compare the supposed cultural proclivities of Americans or Japanese for or against litigation. Before even getting to dispute resolution, however, a more basic difference may be where official documents come from.

Americans think it is natural to go to court to accomplish divorces, adoptions, or settle inheritance issues even when there is no dispute. They may also think court decrees are the normal form of official proof of status in such matters.

The reliance on courts in these areas is more a reflection of the history of Anglo-American law, including the influence of Christianity, which meant divorce was disfavored and difficult well into the 20th century. Moreover, before modern government institutions existed, courts were one of the few institutions capable of producing an official document—a judgment—that could be used to prove status or ownership.

However, if one were to design a modern system of government from scratch—what the leaders of Meiji Japan essentially did—requiring everyone to go to court to accomplish routine family transactions would be irrational. Thus, the lesser role of courts in Japan compared to the United States is in part due to the comparatively modern design of Japanese government systems.

Japan’s koseki (family registration) system is a prime example of this difference, one that seems particularly hard for Americans to understand. The koseki is used to register births, marriages, divorces, deaths, adoptions, and other changes in personal or family status. An extract of a person’s koseki issued by the appropriate municipal office serves as official proof of marital status, parenthood, and adoptive relationships.

Americans can use a marriage certificate to prove they got married to a particular person on a particular date in the past and a divorce decree to show they got divorced. However, they would likely find it impossible to prove that they are still married or still single today. Because divorce and other changes of status must be registered to have legal effect, the koseki provides both a snapshot of a person’s current legal family situation as well as a historical record of it over their entire life.

Because it presents a complete historical record of a person’s life, while Americans typically must go to probate court to settle the estate of a dead relative, in Japan koseki records of the deceased and his heirs may be sufficient proof of inheritance rights to allow a transfer of estate property without any court involvement.

Japanese courts do get involved in divorce and estate matters, but only if there are disputes among the parties involved or other complicating factors. Even then, the court decree is not used as a form of identity document, since any aspect of it that is relevant to third parties (a divorce, for example, since marital status is appropriate to property rights and liability for marital debts) will be reflected in the relevant koseki.

This is an important difference. American lawyers attach tremendous importance to what a court decree says in a divorce or child custody case. A Japanese lawyer can offer an explanation of how Japanese courts handle such disputes that will seem very familiar to her American counterpart, but may also be highly misleading if she does not mention that court involvement is optional. 90% of Japanese divorces are accomplished by the parties simply filing the relevant paperwork with the koseki authorities; court orders are unimportant as evidence of status.

Not only do Americans have to go to court when Japanese do not, because the US legal system involves multiple states each with its own system of courts, American lawyers are very concerned about whether a court has jurisdiction over any particular case. In order to prevent “forum shopping,” there is typically a residency or other waiting period that must pass before a party can bring certain types of cases. By contrast, Japan has a single system of courts and, in any case, whether they have jurisdiction is irrelevant to matters of personal status unless there is a dispute. In fact, Japanese people can get married or divorced from anywhere in the world by making koseki filings through a Japanese consulate.

Certainly there are things to criticize about the system as well. It is inexorably linked to Japanese nationality, meaning that foreigners are subject to different treatment. In combination with the Civil Code family law rules, some of which still date back to the 19th century, the koseki is inflexible regarding the types of family relationships that can be reflected in it. It also perpetuates presumptions of paternity, distinctions based on legitimacy and usage of surnames that some consider no longer appropriate for modern Japanese society.

This assumes family law is for family members—an assumption many Americans may take for granted since theirs is based mostly on present or former family members asserting rights against each other in court. Yet, the koseki is essentially a system of family law for the government and other third parties, one that confirms unambiguously those aspects of a particular individual’s family status relevant to people outside the family for purposes of property rights, parental responsibility, and liability for debts.

This aspect of the system was arguably more important back when koseki records were accessible to anyone and the koseki embodied the ie system of the past and under which multiple families might be subject to the authority of a single “head of household”—a legal status that was registered and heritable, and came with rights to dispose of family property and duties to ensure compliance of the family with tax and other public duties. The ie system was dismantled under the postwar occupation as incompatible with the current egalitarian Constitution.

Japanese society has changed dramatically since the modern koseki system was first introduced. Couples are marrying later or not at all. Fewer people are having fewer children. More people—women in particular—are seeking financial independence and professional accomplishment outside of “traditional” family structures and naming conventions. Privacy about family status has also become a very powerful value, coupled with increased sensitivity about the ways in which family background can be a source of discrimination. And globalization has increased the need to address the needs of non-Japanese people in Japan who exist outside the koseki system.

Similarly, although all koseki are associated with a particular location, the system is no longer directly related to residence; a separate system of residence registry is used for tax and benefits purposes.

Moreover, “My Number” personal identification codes were introduced in 2015 as part of the government’s ongoing efforts to rationalize the tax and public social welfare programs. Over time the My Number system is expected to be used more broadly, including in ways that obviate the need to use koseki extracts as identification.

Thanks to modern technology, the koseki seems likely to become less important. But the rational nature of its design and its utility as a tool of social ordering is still worth understanding, and some of its positive aspects should be appreciated in comparison to possible alternatives.

Colin P.A. Jones is a law professor, Doshisha Law School at Kyoto.