The “marriage equality movement”: that’s the name chosen for themselves by same-sex “marriage” supporters. The implicit argument is that the state’s granting marriage licenses only to opposite-sex couples is undue discrimination. The claim has an initial plausibility: the state grants a marriage license to John and Mary but not to Jim and Steve. Isn’t that unequal treatment? But this charge, I will show, rests on a profound confusion about both marriage and equality. A state’s recognition that marriage is only between a man and a woman is not unjust. What’s more, a state’s endorsement of same-sex “marriage” does create an arbitrary and invidious discrimination.

A law is unjust only if the distinction it creates is not essentially related to a legitimate purpose of law. But whatever one holds about the morality of homosexual acts, it is clear that the state does have an interest in promoting and regulating marriage as traditionally defined, and that the sexual relationships of same-sex couples are distinct in kind from that. So, even if—contrary to fact—the state did have an interest in promoting same-sex sexual relationships, that interest would be different from the one served by promoting marriage. And so the two types of relationships or arrangements should not be lumped together. Moreover, falsely to equate the two is to obscure the nature of marriage.

What is marriage? The traditional view of marriage is: the union of a man and a woman, who have consented to share their lives, on the bodily (sexual), emotional, and spiritual levels, in the kind of community that would be fulfilled by having and raising children together.

Two points need emphasis here. First, marriage is a bodily union, as well as emotional and spiritual. For in sexual intercourse—which consummates the marital union—the spouses become biologically one: they complete each other to form a single subject of a single biological action, the kind of action that could procreate, provided conditions outside their conduct are present. This biological union (a procreative-type act) embodies their procreative-type union (provided they have consented to share their lives in that kind of union).

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Second, marriage is the kind of union whose fruition is procreation. It is the kind of union that would be fulfilled by having and raising children together; the union of the spouses is embodied, prolonged, and enriched by enlarging into family. Still, marriage is not a mere means in relation to procreation, but a sharing of lives (bodily, emotionally, and spiritually) that is good in itself—and so a man and a woman who have consented to such a multi-leveled union are genuinely married, and have an intrinsically fulfilling marital union, even if it turns out they cannot procreate together.

Now of course not all agree with the traditional definition of marriage. But the point I want to make is simply this: marriage, as traditionally defined, is a distinct type of community and not an arbitrary set. Unmarried cohabitators have a different type of relationship. Alliances to raise children also are not necessarily marriages: a group of celibate religious women running an orphanage, for example, are not married. And, plainly, same-sex sexual relationships are a different kind of relationship: they cannot become biologically one, nor is their relationship of the kind that would find its fruition in conceiving, bearing, and raising children together. (True, same-sex partners can form an alliance to raise children—for example, those from a previous marriage or produced by artificial reproduction; but that alliance is not an extension or prolongation of a bodily-emotional-spiritual union already begun, as is the case in marriage.)

Now it is precisely the distinctive features of marriage that ground the state’s interest in promoting and regulating it, and that make the general strength or health of marriage a public good. First, marriage is a distinctive way in which men and women are fulfilled, an irreducible aspect of their flourishing, and one that can be easily misunderstood. And so marriage needs cultural support—and can be harmed by cultural confusion about it. Clarity within the general culture about the value and nature of marriage enables young men and women, as well as those already married, to participate more fully than they otherwise would in this distinctive good—just as a clear public understanding of health or learning assists individuals and families to participate more fully in those goods.

Second, while good in itself, and not a mere means to an extrinsic end, marriage also provides the crucial social function of encouraging parents (and potential parents) to commit to each other and to whatever children they may have. A healthy and strong marriage culture will provide the safest and healthiest environment for children. For these reasons it is in everyone’s interest for the state to promote a sound understanding of marriage, and certainly to avoid obscuring its nature.

Since a same-sex couple is unable to form the kind of union marriage is, not granting same-sex couples marriage licenses is simply a decision by the state not to engage in a confusing and harmful fiction. Marriage is a certain kind of union. Denying a marriage license—or the privileges, protections, and obligations of marriage—to those who are unable to marry is not unjust discrimination. The state denies marriage licenses to threesomes or foursomes (refraining from declaring polyamorous groups marriages) and denies marriage licenses to twelve-year-olds (requiring valid consent for a marriage). These denials are not unjust because threesomes, foursomes, and twelve-year-olds are unable to form the kind of union that marriage is. But the same is true of same-sex couples. So, just as the distinction between eighteen-year-olds and twelve-year-olds is relevant to the purpose of marriage—because the former but not the latter are actually able to form the union that is marriage—in the same way, the distinction between opposite-sex couples and same-sex couples is relevant to the purpose of the marriage laws, because the former but not the latter can actually form the kind of union that marriage is.

According to same-sex “marriage” proponents, the public interest served by marriage laws is the stability of households. For example, in striking down California’s pro-marriage constitutional amendment called Proposition 8, Judge Vaughn Walker claimed: “The state regulates marriage because marriage creates stable households, which in turn form the basis of a stable, governable populace.” Stability of households might of course be a legitimate public aim, but laws to promote that (and to provide benefits and privileges for stable households as such) are not marriage laws. Such laws, benefits, and so on, would—if applied justly—have to be given also to groups who do not have sexual relationships and groups not pledging permanence and exclusivity.

Clearly, though, same-sex “marriage” supporters want much more than certain benefits and privileges. Discussion of concrete benefits such as hospital visitation, inheritance rights, and so on, is really a side issue—such benefits could be secured by other means for individuals who need them (for example, a durable power of attorney for health care, a will, etc.). Nor—contrary to how it is usually portrayed—is the same-sex marriage proposal aimed at tolerance, since persons with same-sex attractions are already free to engage in private sexual behavior and to establish for themselves long-term romantic and sexual relationships. Rather, what proponents of same-sex “marriage” principally desire is the social affirmation and endorsement of homosexual relationships as such. Judge Walker indicated this point clearly in his Proposition 8 decision: “Plaintiffs [some same-sex couples] seek to have the state recognize their committed relationships . . . . Perry and Stier seek to be spouses; they seek the mutual obligation and honor that attend marriage.”

So, the proposal is for the state to promote something called marriage, and that marriage is to be understood in a way that will include same-sex partners. This sounds like old news. But what, on their view, is the thing called “marriage,” and why should the state promote it? What distinguishes marital unions from others, such that the state should promote them? One cannot just pronounce that these couples will now count as married; there must be something one means by “being married,” something held in common by all married couples. But the same-sex “marriage” position cannot provide a coherent account of what that something is.

If marriage is not a bodily, emotional, and spiritual union of a man and a woman, of the kind that would be fulfilled by procreation, then what makes a union marriage and why should the state support it? It is not simply a union that is formed by a wedding ceremony: that would be a circular definition. Nor is every romantic and sexual relationship a marriage, and certainly there is no point in the state promoting all such relationships. Perhaps one will say that it is a stable, committed, and exclusive romantic-sexual relationship. But how stable would a romantic-sexual relationship need to be in order to be a marriage? Suppose John and Mary have a romantic-sexual relationship while college students but plan to go their separate ways after graduation: is that stable enough to be a marriage? If not, why not?

Or suppose Joe, Jim, and Steve have a committed, stable, romantic-sexual relationship among themselves—a polyamorous relationship. On what ground can the state promote the relationship between couples, but not the relationship among Joe, Jim, and Steve? The argument here is not a slippery slope one. Rather, the point is: There must be some non-arbitrary features shared by relationships that the state promotes which make them apt for public promotion, and make it fair for the state not to promote in the same way other relationships lacking those features. Without this the distinction is invidious discrimination. The conjugal understanding of marriage has a clear answer: (a) marriage is a distinct basic human good, that needs social support and that uniquely provides important social functions; (b) marriage’s organic bodily union and inherent orientation to procreation distinguish it from other relationships similar in superficial respects to it. But the same-sex marriage proposal’s conception of marriage has no answer. In fact, its conception of marriage is actually an arbitrarily selected class, and so the enactment of this proposal would be unjust.

The problem is not solved if one adds to one’s description or definition of marriage, that it must be a permanent commitment (as Judge Margaret Marshall did in her decision striking down Massachusetts’ marriage law: “It is the exclusive and permanent commitment of the marriage partners to one another, not the begetting of children, that is the sine qua non of civil marriage”). For it is fair to ask: why should the commitment be exclusive and permanent? The college students’ relationship (lacking permanence) and the celibate monks’ relationship (lacking exclusivity—others can join the religious order), both form households and contribute to social stability. In contrast, the conjugal understanding of marriage allows a clear answer to these questions: since marriage is a bodily and procreative-type union, and an irreducible basic good, it is non-arbitrarily distinct from other types of relationships. The promotion of this kind of relationship, for its own sake (because it is a basic good), and for the sake of children generally (since a strong marriage culture provides a safe haven for children), makes it in accord with justice to recognize, as marriage, only a relationship between a man and a woman, pledged to be permanent and exclusive. The conjugal conception of marriage is just and coherent; the same-sex marriage proponents’ conception of marriage is unjust and incoherent.