Determinants of fertility differ across countries, and, to some extent, across regions with shared social, economic, political, and cultural backgrounds. Therefore, I would like to refine the theme, “What is likely to be the most important factor influencing future fertility trends?”, by limiting my geographical focus to Japan, the country I am mainly studying. But my research on Japan is also relevant to other East Asian societies that have similar cultural backgrounds and fertility trends shaped by similar socioeconomic developments:² namely, South Korea, Taiwan, and, to some extent, mainland China. These countries share, to varying degrees, family norms influenced by the tradition of Confucianism and its emphasis on patriarchal parent-child relationships, gender-based role specialization, and hierarchal relationships based on seniority (Cheng 2020). The region also includes countries/regions with some of the world’s lowest fertility rates: Taiwan (TFR: 0.90 in 2010), South Korea (TFR: 0.98 in 2018), and Japan (TFR: 1.25 in 2005). I would like to use this opportunity to share some thoughts on why fertility is so low in East Asia by (primarily) examining Japanese data; and to discuss what I see as being the most important determinant of future fertility trends in Japan and other East Asian countries.

In my view, the most important factor influencing fertility trends in Japan – and most likely in other East Asian countries as well – has been and continues to be marriage. In the following, I will elaborate on this view by providing some empirical evidence.

First, it is clear that marriage is essentially the only type of union in which couples have children in Japan and in East Asia. The proportion of births outside of marriage in Japan was only 2.2% in 2017, up from 0.8% in 1980 (Ministry of Health, Labor and Welfare (hereafter, MHLW) 2018). Similarly, in South Korea, the proportion of births outside of marriage increased from 1.1% in 1981 to just 1.9% in 2017 (Korean Statistical Information Service 2019). The very high share of marital births in East Asia makes singlehood a strong proxy for childlessness. At the same time, the timing of marriage strongly influences completed levels of marital fertility in Japan. The female mean age at first marriage has been increasing continuously since the early 1970s, rising from 24.2 in 1970 to 29.4 in 2014, and levelling off thereafter. As a result of this trend, the completed fertility of married women in Japan – which is measured as the average number of children born to women in a first marriage who have been married for 15–19 years – was stable from 1982–2002 (1982: 2.23, 2002: 2.23), but has declined slightly since then, and had fallen to 1.94 by 2015 (National Institute of Population and Social Security Research (hereafter, NIPSSR) 2017a).

The extremely low prevalence of extramarital childbearing in Japan can be seen as a cultural norm (Hertog and Iwasawa 2011), but it can also be explained from a legal point of view. A large share of the growth in non-marital childbearing in Western societies is attributable to increased childbearing within consensual unions; thus, the prevalence of non-marital childbearing is at least partly related to the legal status of non-marital consensual unions (Perelli-Harris and Sánchez Gassen 2012). Although scholarly attention to this issue has been lacking, common-law marriage in Japan is a legally defined consensual union that is comparable to non-marital unions in Western countries. Couples in common-law marriages intend to live as spouses, even though their relationship is not legally registered as married. The prevalence of common-law marriage relationships in Japan is not fully known, as the civil registration of such unions is not required, and these couples are often recorded as “married” in censuses or in other representative social/demographic surveys. In Japan, common-law marriage is similar in form to legal marriage. For example, the couples in these relationships share a residence and have legal obligations to provide mutual economic support and sexual exclusivity. Couples in common-law marriages in Japan are also entitled to the same social security benefits as married couples, such as national health insurance, pension, and other public assistance benefits.³ However, the marital benefits in the taxation system do not apply to couples in common-law marriages. When dissolving their relationship, the partners in a common-law marriage are also entitled to the same legal rights as married couples, such as the right to divide their mutual assets or to claim compensation if the other partner is responsible for the dissolution. But, in general, union dissolution is easier in common-law marriage than in legal marriage in Japan because the dissolution of a common-law marriage does not require the use of formal administrative procedures to deregister the marriage in the family register system.

However, legal marriage and common-law marriage differ significantly in terms of the legal protections and legal rights they confer, not only with respect to the relationship, but to the couple’s children. First, whereas the right of inheritance from a deceased partner is based on agreements made by the couple in a common-law marriage, the partners in a married couple are automatically entitled to inherit from one another. Second, and most importantly, when a child is born within a common-law marriage, the child is registered as “illegitimate,” and the custody of the child is awarded exclusively to the mother. By contrast, when a child is born to married parents, the mother and the father automatically share custody. Furthermore, a newborn child of parents in a common-law marriage needs to be recognized by the biological father in order to receive obligatory support from him. Without this recognition, the child would not even have a right to inherit from the biological father. In addition to these differences, the existence of a common-law marriage relationship is often difficult to prove because there is no official record of this relationship, particularly if both parties contribute to the social security system separately. Moreover, the distinction between common-law marriage and unmarried cohabitation is rather fuzzy, as it is based solely on whether the partners “consider” their relationship to be an alternative to legal marriage. Therefore, claiming the legal rights associated with common-law marriage is not straightforward, especially when the partners are in conflict with each other. Thus, under current civil law in Japan, there is little incentive for couples, and for women in particular, to have a child outside of legal marriage.

As I discussed above, marriage is currently the only broadly accepted setting for childbearing among Japanese couples, and there is little indication that non-marital childbearing is becoming more common in Japan, or is likely to do so in the future. However, this does not necessarily mean that marriage will continue to be an important factor in future fertility in Japan. In fact, there are slight but important signs of changes in the pathways to marriage and fertility within marriage. In this section, I will describe these new trends, and examine whether they signal the emergence of some broader changes in the marriage-fertility nexus.

Assuming that marriage continues to play a major role in determining fertility trends in Japan and East Asia, what is the most important factor influencing marriage trends?

A large body of research has examined the relationship between education and first marriage in East Asia. Education appears to be one of the most important factors influencing marriage rates. Participating in education provides young people with opportunities to meet potential partners. Educational attainment serves as a proxy for longer-term earnings potential and economic stability (Blossfeld and Timm 2003), and determines the timing of marriage. Indeed, the expansion of male and female tertiary education and the decline in first marriage are among the most prominent social changes in East Asia.

One of the consistent findings regarding East Asian marriage trends is a negative educational gradient in female marriage, which is thought to reflect gender role specialization based on the male breadwinner/female homemaker model of marriage (Blossfeld and Timm 2003). However, recent studies have shown a weakening or even a reversal of this relationship in Korea (Park and Lee 2017), Hong Kong (Zhou et al. 2017), Taiwan (Cheng 2014), and Japan (Fukuda et al. 2019). My recent study with colleagues illustrated that during the 1990–2015 period, the negative educational gradient in female marriage in Japan first disappeared around 2005, and then turned positive after 2009 (Fukuda et al. 2019). This shift in the educational gradient was brought about by a combination of a decline in the marriage rates of less educated women and an increase in the marriage rates of highly educated women. The former finding is consistent with expectations derived from theories on globalization and labor market bifurcation (e.g., the concentration of non-standard employment in less educated groups); whereas the latter finding is consistent with predictions stemming from the gender revolution framework, including the expectation that highly educated women have a more advantaged position on the marriage market (Fukuda et al. 2019). These patterns of change are generally consistent with trends documented in the U.S. and in many other wealthy countries. It should be noted that the ideational shift toward dual-earner marriage – which is likely to be facilitated by both economic uncertainty and the preference for more gender-equal sharing of economic roles – will be an important factor influencing marriage trends in Japan, and possibly in other East Asian societies in which highly educated young adults have become a majority in the marriage market. Given these findings, it is likely that policies aimed at supporting female employment and work-family balance will have a positive impact on both marriage and childbearing.

In this short article, I provided my thoughts on the factor that is most likely to influence future fertility trends in Japan, while drawing on a wide range of available data. My conclusion is that marriage continues to be the most important proximate determinant of future fertility in Japan, and, arguably, in other East Asian societies as well. Marriage itself is being affected by the trends in female tertiary education and the concurrent shift toward a dual-earner marriage ideology. However, I am aware that future fertility trends may not conform to a simple extrapolation of current fertility behaviors. For instance, young adults’ dating behaviors and the pathways to marriage are changing; marriage has become less stable; and marital fertility is declining. These changes may also reshape the link between marriage and fertility trends in the future.