If marriage were simply a form of sexual-romantic companionship or domestic partnership, then the equal protection clause of the Constitution’s Fourteenth Amendment would require the Supreme Court to strike down state laws limiting marriage licenses to male-female partners.

There would be no principled basis for distinguishing opposite- from same-sex relationships—or, for that matter, from multiple-party (“polyamorous”) ones. Any two (or more) people can feel affection for one another, believe that the quality of their relationship is enhanced by mutually agreeable sexual acts, and make a commitment to caring and sharing. So if our law understood these things as the essence of marriage, then restricting it to two-person, opposite-sex partnerships would be invidiously discriminatory—a denial of equal protection.

Historically, however, our matrimonial law has not conceived marriage as mere sexual-romantic companionship or domestic partnership; nor is there anything in the text, logic, structure, or historical understanding of the Constitution that commits the nation to such a conception of marriage.

In fact, the Constitution does not attempt to settle the question of how marriage should be defined. It dictates no choice among competing conceptions of what marriage is. It does not, for example, forbid polygamy or require states to permit it. Nor does it choose between marriage conceived as a genderless institution and marriage as the conjugal union of husband and wife. Rather, the Constitution leaves the choice among competing conceptions of marriage where it leaves most policy questions, namely, to the judgment of the people and their elected representatives.

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State Marriage Laws: Rooted in History, Biology, and Psychology

So, historically, how have the states understood and defined marriage?

They have understood and defined it as a relationship shaped by the needs of children for mothers and fathers, rather than as an institution whose purpose is to serve the interests or desires of adults by facilitating sexual-romantic companionship. Our laws, including those under review in the cases now pending before the Supreme Court, reflect the judgment that marriage is the conjugal union of spouses, rooted in the sexual-reproductive complementarity of male and female, which brings together a man and a woman as husband and wife to be father and mother to any children born of their union. As a social institution, it aims to secure for children the inestimable blessing of being brought up in the committed love—the marital bond—of the man and woman whose union brought them into being, and the related benefit of both maternal and paternal influences and care.

This understanding of marriage as a conjugal union recognizes that not all married couples will have children, though most will. But it responds to the biological fact that every child will have a mother and a father, and recognizes the psychological reality that children generally long to know and be known by, and to love and be loved by, both their fathers and their mothers. And it is built upon the fact  that the social purpose of legally recognizing and supporting marriage as an institution—the goal that gives the state any legitimate interest in marriage—is to ensure that as many children as possible are brought up by their father and mother in the marital bond. After all, the state has no interest whatsoever in the romantic lives of its citizens as such.

But what about the fact that some married couples cannot have children? Does that show that marriage cannot really be a conjugal relationship, but does in the end boil down to sexual-romantic companionship?

No. Our law, and the traditions of thought that have informed and supported it, have always understood marriage as the type of relationship that would naturally be fulfilled by the spouses having and rearing children together. And sexually complementary spouses can enter into precisely that type of relationship even when one or both happen to be infertile.

This understanding of the matter simultaneously and perfectly coherently holds two important truths: (1) the very idea of marriage is rooted in the male-female complementarity that makes sexual reproduction possible, and (2) the value of marriage cannot simply be reduced to its utility as a means to the end of having and properly rearing children. Men and women are so constituted that being in a marriage—a sexually complementary relationship that, as such, is naturally ordered to procreation and that would be fulfilled by having and rearing children together—is valuable in itself, and not merely as a means to something else, even where that something else is the great good of having and rearing children.

The Constitution Doesn’t Adjudicate between Competing Conceptions of Marriage

As a matter of constitutional law, defenders of state marriage statutes need not show that the conjugal conception of marriage is superior to the idea of marriage as mere sexual-romantic companionship or domestic partnership (though I certainly believe it is).

The question before the Court is whether the Constitution requires states to adopt the latter conception of marriage. Clearly, it does not. Thus, state laws defining marriage as the conjugal union of husband and wife do not violate the equal protection guarantee, and there is no constitutional warrant for the Court’s imposing a genderless conception of marriage on the country, even if a majority of justices happen to favor such a conception as a matter of social policy. Courts are not legislatures, and judges should not usurp legislative authority, even for the sake of a cause they personally happen to believe represents social progress.

Still, it is worth noting that the historical understanding of marriage as a conjugal union has the immense advantage over the revisionist alternative of being able to provide a principled basis for the norms that even today most people believe pertain to marriage: (1) that it should be a union of two persons, not three or more; (2) that it should be sexually closed and not “open” (even by consent of both spouses); (3) that it should be pledged to permanence, and not conceived as a temporary alliance (for a set term, or “for as long as love lasts”).

But wasn’t marriage once defined as a same-race relationship, with interracial marriages being banned? Didn’t the Supreme Court strike down anti-miscegenation laws as unconstitutional limitations on the freedom to marry? Aren’t laws defining marriage as conjugal (opposite-sex) guilty of the same offense?

Protecting Marriage as a Conjugal Union Is Not Analogous to Racism

Throughout history and across cultures, marriage has been defined as a conjugal partnership precisely because the sexual-reproductive complementarity of man and woman has been understood as central to it. That has been true even in cultures that permit polygamy. Race was generally not regarded as having anything to do with what marriage is or the social purposes it served. After all, a man and a woman of different races can unite in a bond of precisely the sort that is oriented to procreation and would be fulfilled by their having children together.

Anti-miscegenation laws were innovations that were introduced in certain states of the United States and a few other jurisdictions for one purpose only: to sustain and reinforce a vicious system of white supremacy and racial subordination and exploitation that began with race-based chattel slavery. These laws did not treat interracial marriage as impossible or a contradiction in terms, but rather prohibited people from entering into such marriages and punished them if they did. The objective of these laws was not the laudable one of maximizing the odds that children would grow up with the blessing of both a mother and a father in their lives. The goal, rather, was the ignoble one of maintaining “racial purity” and preventing the “mongrelization” of the allegedly superior race.

In the case of Loving v. Virginia, the Supreme Court struck down anti-miscegenation laws precisely because they represented and reinforced just the kind of racial injustice that the Fourteenth Amendment was enacted to dismantle. The racial classifications these laws introduced were rooted in sheer prejudice and lacked any rational basis or relationship to a legitimate governmental interest.

By contrast, conjugal marriage laws did not arise out of racism, sexism, or any other form of bigotry. They were created and became the norm virtually everywhere for the vital purpose of bringing the two sexes together in a bond that is uniquely apt for nurturing and educating children. The idea of marriage as a conjugal partnership is not rooted in the bigoted belief that any person or group of persons is inherently inferior to any other, but rather in the understanding that moms and dads are not substitutable—both are necessary for parenting.

The goal of anti-miscegenation laws was to keep the races apart—so that one could exploit the other. The point of conjugal marriage laws is to bring the sexes together—so that as many children as possible can be brought up in the committed bond uniting their parents. Racial sameness has nothing to do with marriage. Sexual difference—complementarity—is central to the very concept of marriage. Indeed, but for the fact that human beings happen to be among the types of creatures that reproduce sexually, no culture would ever have conceived the idea of marriage.

For the Court to strike down laws defining marriage as the conjugal union of husband and wife would be to abolish the idea that men and women matter—equally—in the lives of the children they create. And it would be both a judicial usurpation of legislative authority and a federal intrusion into a matter left by the Constitution in the hands of the states.