Everyone agrees that marriage, whatever else it is or does, is a relationship in which persons are united. But what are persons ? And how is it possible for two or more of them to unite? The view typically (if often unconsciously) held by advocates of liberal positions on issues of sexuality and marriage is that the person is the conscious and desiring aspect of the self. The person inhabits (or is somehow associated with) a body, certainly, but the body is regarded (if often only implicitly) as a subpersonal reality, rather than a part of the personal reality of the human being whose body it is. The body is viewed as an instrument by which the individual produces or otherwise participates in satisfactions and other desirable experiences and realizes various goals.

For those who formally or informally accept this dualistic understanding of what human beings are, personal unity cannot be achieved by bodily union. Persons instead unite emotionally (or, as those of a certain religious cast of mind say, spiritually ). And, of course, if this is true, then persons of the same sex can unite and share sexual experiences together that they suppose will enhance their personal union by enabling them to express affection, share pleasure, and feel more intensely by virtue of their sex play.

The alternate view of what persons are is the one embodied in both the historic law of marriage and what Isaiah Berlin once referred to as the central tradition of Western thought. According to this view, human beings are bodily persons, not consciousnesses, or minds, or spirits inhabiting and using nonpersonal bodies. A human person is a dynamic unity of body, mind, and spirit. Far from being a mere instrument of the person, the body is intrinsically part of the personal reality of the human being. Bodily union is thus personal union, and comprehensive personal union”marital union”is founded on bodily union.

The bodily unity of spouses is possible because human males and females, like other mammals, unite organically when they mate”they form a single reproductive principle. Although reproduction is a single act, in humans (and other mammals) the reproductive act is performed not by individual members of the species but by a mated pair as an organic unit. The point has been carefully explained by Germain Grisez:

Though a male and a female are complete individuals with respect to other functions”for example, nutrition, sensation, and locomotion”with respect to reproduction they are only potential parts of a mated pair, which is the complete organism capable of reproducing sexually. Even if the mated pair is sterile, intercourse, provided it is the reproductive behavior characteristic of the species, makes the copulating male and female one organism.

What is unique about marriage is that it truly is a comprehensive sharing of life, a sharing founded on the bodily union made uniquely possible by the sexual complementarity of man and woman”a complementarity that makes it possible for two human beings to become, in the language of the Bible, one flesh”and thus possible for this one-flesh union to be the foundation of a relationship in which it is ­intelligible for two persons to bind themselves to each other in pledges of permanence, monogamy, and fidelity.

People who reject this understanding of sex and marriage say that “Love makes a family.” And it does not matter whether the love is between two people of opposite sexes or the same sex. (Those who are clearheaded and candid acknowledge that, by the same token, it would not matter if the love were among three or more people.) Nor does the sexual expression of that love make any difference.

In fact, however, at the bottom of the contemporary debate over marriage is a possibility that defenders of conjugal marriage affirm and its critics deny: the possibility of marriage as a one-flesh communion of persons. If acts that fulfill the behavioral conditions of procreation (whether or not the nonbehavioral conditions happen to obtain) are, in fact, capable of uniting spouses interpersonally”thus providing the biological matrix of the multilevel union and sharing of life that marriage is, according to the traditional understanding long embodied in Western law, philosophy, and culture”then truly marital acts differ fundamentally in meaning, value, and significance from intrinsically nonmarital sex acts (such as acts of sodomy and mutual masturbation).

Arguments that true marriage is something other than or broader than the union of two sexually complementary spouses necessarily suppose that the value of sex must be instrumental either to procreation or to pleasure, considered as an end in itself or as a means of expressing affection, tender feelings, etc. Thus, critics of traditional norms of marriage and sexuality say that homosexual sex acts, for example, are indistinguishable from heterosexual acts whenever the motivation for such acts is something other than procreation. That is to say, the sexual acts of same-sex partners are indistinguishable in motivation, meaning, value, and significance from the marital acts of spouses who know that at least one spouse is temporarily or permanently infertile. Thus, the argument goes, the traditional understanding of marriage is guilty of unfairness in treating sterile persons of opposite sexes as capable of marrying while treating same-sex partners as ineligible to marry.

Stephen Macedo has accused the traditional view and its defenders of precisely this “double standard.” He asks: “What is the point of sex in an infertile marriage? Not procreation: The partners (let us assume) know that they are infertile. If they have sex, it is for pleasure and to express their love, or friendship, or some other good. It will be for precisely the same reason that committed, loving gay couples have sex.”

Many people find this sort of criticism impressive, and even some conservatively oriented people seem to find themselves stumped by it. Once the core of the traditional view is brought into focus, however, it is clear that the criticism straightforwardly fails because it presupposes that the point of sex in marriage can only be instrumental. It is a central tenet of the traditional view, however, that the point of sex is the good of marriage itself, consummated and actualized in and through sexual acts that unite spouses as one flesh and, thus, interpersonally.

The traditional view rejects the instrumentalizing of sex (and, thus, of the bodies of sexual partners) to extrinsic ends of any sort . Of course this does not mean that procreation and pleasure are not rightly sought when they are integrated with the basic good and justifying point of marital intercourse, namely, the one-flesh union of marriage itself.

Critics of the traditional understanding of marriage who grasp this point must therefore argue that the apparent one-flesh unity that distinguishes marital intercourse from sodomitical and other nonmarital sex acts is illusory and, thus, that the apparent bodily communion of spouses in acts that fulfill the behavioral conditions of procreation is not really possible.

Macedo, for instance, claims that “the ‘one-flesh communion’ of sterile couples would appear . . . to be more a matter of appearance than reality.” Because of their sterility, such couples cannot really unite biologically: “Their bodies . . . can form no ‘single reproductive principle,’ no real unity.” Indeed, Macedo argues that even fertile couples who conceive children in acts of sexual intercourse do not truly unite biologically, because, he says, “penises and vaginas do not unite biologically, sperm and eggs do.”

John Finnis has aptly replied that “in this reductivist, word-legislating mood, one might declare that sperm and egg unite only physically and only their pronuclei are biologically united. But it would be more realistic to acknowledge that the whole process of copulation, involving as it does the brains of the man and woman, their nerves, blood, . . . secretions, and coordinated activity is biological through and through.” Moreover, as Finnis points out, “The organic unity which is instantiated in an act of the reproductive kind is not,” as Macedo reductively imagines, “the unity of penis and vagina. It is the unity of the persons in the intentional, consensual act” of sexual intercourse.

The unity to which Finnis here refers”unity of body, sense, emotion, reason, and will”is central to our understanding of humanness. Yet it is a unity of which Macedo and others who deny the possibility of true bodily communion in marriage can give no account. For this denial presupposes a dualism of person (as conscious and desiring self), on the one hand, and body (as instrument of the conscious and desiring self), on the other hand, which is flatly incompatible with this unity. This dualism of person and body is implicit in the idea, central to Macedo’s denial of the possibility of one-flesh marital union, that sodomitical acts differ from what law and philosophy have traditionally regarded as chaste and honorable marital acts only as a matter of the arrangement of the “plumbing.” According to this idea, the genital organs of an infertile woman or man are not really “reproductive organs” any more than, say, mouths, rectums, tongues, or fingers are reproductive organs. Thus, the intercourse of a man and a woman, where at least one partner is infertile, cannot really be an act of the reproductive type.

But the plain fact is that the genitals of men and women are reproductive organs all of the time”even during periods of sterility. Acts that fulfill the behavioral conditions of procreation are acts of the reproductive kind even where the nonbehavioral conditions of procreation do not obtain. Insofar as the point of sexual intercourse is marital union, the partners achieve the desired unity (become “two-in-one-flesh”) precisely insofar as they mate or, if you will, perform the type of act on which the gift of a child may supervene”what traditional law and philosophy have always referred to interchangeably as “the act of generation” and “the conjugal act.”

Now, in some sectors of our culture, the views advanced by Macedo are hardly considered radical. On the contrary, his views about sex and marriage are ­considered by many to be too conservative, even old-fashioned. He and other defenders of this “moderate liberal” position have been taken to task for affirming the principle of sexual fidelity and criticizing, if usually only implicitly, promiscuity. They have an admirable commitment to the notion of marriage as a permanent and exclusive sharing of life integrated around (but certainly not reducible to) sexual activity. But they think that the nature of the sexual activity just does not matter. Sex is sex. It cannot really unite people as one flesh, but it can enable them to express their affection in a special way.

Once marriage and marital intercourse are thus reduced to the status of instrumental goods, the only intelligible point of entering into marriage will be the achievement of some other end or ends. For some, certainly, the end of marriage will be procreation, but whether a particular marriage is a “reproductive alliance” or an alliance for purposes entirely unrelated to reproduction is purely a matter of the subjective preferences of the parties entering into the alliance. In no way is marriage considered to be naturally ordered to the coming to be and nurturing of children. Nor are the contours of the marital state or the terms of the marital relationship understood to be established or shaped by a natural orientation toward child rearing.

Marriage, on this revised understanding, is marked by a plasticity or malleability that sharply distinguishes it from the conception of marriage it is proposed to replace. In this revisionist understanding, marriage is also unnecessary”even for child rearing. If two (or perhaps more) people find, or suppose, that the state of being married works for them, then they have a reason to marry. If not, then marriage is not as a matter of principle understood to be a uniquely, or even especially, apt context for them to structure their lives together.

What about sex? What is the point of that in the revised conception of marriage? What is sometimes referred to as lifestyle liberalism (to distinguish it from the political liberalism of, say, Franklin Roosevelt or Hubert Humphrey) rejects the view that sex is to be restricted to the marital relationship. It certainly has no ground of principle to object to sexual cohabitation outside of marriage. And even with regard to sex apart from stable relationships, lifestyle liberalism is “nonjudgmental.” Its main principle of rectitude in sexual matters is the principle of consent, not, as in the traditional view, the principle of marriage. So long as there is no coercion or deceit in the procurement of sex, sexual choices”as Frederick Elliston, for example”insists, do not raise moral questions.

Even adultery is unproblematic under the lifestyle-liberal conception of marriage if, as in so-called open marriages, there is no deception of a spouse involved. Indeed, under the lifestyle-liberal conception, as defended by Elliston and many others, it is impossible to identify any reason ”there are only subjective preferences”for spouses to demand fidelity of each other. Why should they “forsake all others”? What is the point of sexual fidelity? There is no reason, strictly speaking, not to have an “open marriage””only emotions that some people happen to have and others happen not to have. This is why people who reject the traditional terms of marriage”even those, like Macedo, who do so for putatively conservative reasons, for instance, to make the good of marriage available to people who prefer erotic experiences with partners of their own sex”find it impossible, in the end, to condemn promiscuity and the like, except, occasionally, on pragmatic grounds. Thus Andrew Sullivan, who once framed his case for altering the traditional understanding of marriage in conservative terms, now finds himself affirming the “beauty” and even “spirituality” of anonymous sex”sex among partners who do not even identify themselves to each other by name.

So what is the point of sex in the revised conception? Even if sex is permissible outside of ­marriage, is it nevertheless an intrinsic part of marriage? The answer has to be no. Under the revised conception, the point and value of sex, even in marriage, is instrumental. Marriage is not, in principle, a sexual relationship. If the partners happen to want to have sex with each other, fine”their goals might be to conceive children, to have or share pleasure or intimacy, or to express tender and affectionate feelings toward each other. But not only is it the case that all these goals can be legitimately pursued outside the marital context, it is also the case that there is no reason to pursue them within the marriage”or at all”if the people involved happen not to desire having sex with each other, or at all. Just as you can have sex without marriage, you can have marriage without sex. Thus, the whole idea of marital consummation”an idea historically central to the philosophy and law of marriage in our culture”loses its intelligibility.

A standard revisionist response to the defense of conjugal marriage like the one I am here proposing is the claim that, even if the traditional position is, from the moral viewpoint, true, it is nevertheless unfair for the law to embody it. Macedo, for example, argues that if disagreements about the nature of marriage “lie in . . . difficult philosophical quarrels, about which reasonable people have long disagreed, then our differences lie in precisely the territory that John Rawls rightly marks off as inappropriate to the fashioning of our basic rights and liberties.” So Macedo and others claim that law and policy must be neutral with regard to competing understandings of marriage and sexual morality.

This claim is deeply unsound. The true meaning, value, and significance of marriage are fairly easily grasped (even if people sometimes have difficulty living up to its moral demands) in a culture”including, critically, a legal culture”that promotes and supports a sound understanding of marriage. Furthermore, ideologies and practices that are hostile to a sound understanding and practice of marriage in a culture tend to undermine the institution of marriage in
that culture. Hence it is extremely important that ­governments eschew attempts to be neutral with regard to marriage and embody in their laws and policy the soundest, most nearly correct, understanding.

The law is a teacher. It will teach either that marriage is a reality in which people can choose to participate, but whose contours people cannot make and remake at will, or it will teach that marriage is a mere convention, which is malleable in such a way that individuals, couples, or, indeed, groups can choose to make of it whatever suits their desires, goals, and so on. The result, given the biases of human sexual psychology, will be the development of practices and ideologies that truly tend to undermine the sound understanding and practice of marriage, together with the development of pathologies that tend to reinforce the very practices and ideologies that cause them.

The Oxford philosopher Joseph Raz, a liberal who does not share my views regarding sexual morality, is rightly critical of forms of liberalism, including Rawlsianism, that suppose law and government can and should be neutral among competing conceptions of moral goodness. He has noted, for example, that “monogamy, assuming that it is the only valuable form of marriage, cannot be practiced by an individual. It requires a culture which recognizes it, and which supports it through the public’s attitude and through its formal institutions.”

Of course, Raz does not suppose that, in a culture whose law and public policy do not support monogamy, a man who happens to believe in it somehow will be unable to restrict himself to having one wife or will be required or pressured into taking additional wives. His point, rather, is that, even if monogamy is a key element in a sound understanding of marriage, large numbers of people will fail to understand that or why that is the case”and therefore will fail to grasp the value of monogamy and the point of practicing it”unless they are assisted by a culture that supports, formally by law and policy, as well as by informal means, monogamous marriage. What is true of monogamy is equally true of the other elements of a sound understanding of marriage.

In short, marriage is the kind of good that can be chosen and meaningfully participated in only by people who have a sound basic understanding of it and choose it with that understanding in mind”yet people’s ability to understand it, at least implicitly, and thus to choose it, depends crucially on institutions and cultural understandings that both transcend individual choice and are constituted by a vast number of individual choices.

Robert P. George, a member of the First Things editorial and advisory board, is the McCormick Professor of Jurisprudence at Princeton University. This article is adapted from a speech delivered in New?York City on March 11, 2009 at a meeting of Socrates in the City.