Editor's note: This article was co-authored by Robert George and Sherif Girgis

In our new book What Is Marriage? Man and Woman: A Defense, we make a rational case for the historic understanding of marriage as a conjugal relationship -- a union of a man and a woman at every level (mind, heart, andbody), inherently oriented to family life. We show how the common good depends on enshrining this view in law, and answer all the most significant criticisms of this view (having to do with equality, freedom, neutrality, interracial marriage, infertile couples, and much more). We show how the argument for redefining marriage contradicts itself, and document the many ways that embracing it would harm the common good. And we show how society can support marriage without ignoring the needs, undermining the dignity, or curbing the fulfillment of people with same-sex attractions.

Here, we respond to some challenges that even those sympathetic to our views might raise: Why worry about same-sex marriage in particular? Why worry about marriage policy? If marriage policy does matter, why not "broaden the definition" of marriage to promote family values? How would recognizing same-sex relationships as marriages harm marriage? Isn't ours a losing cause, or at best a secondary one? And why privilege anyone's sectarian values at all -- doesn't that compromise freedom and equality? We address each of these questions in turn.

Why focus on opposing the recognition of same-sex partnerships as marriages? Aren't widespread divorce and single parenting the real problems?

Why do conservatives focus exclusively on same-sex marriage? The answer is simple: We don't. Conservatives always did, and still do, make other social and political efforts to strengthen the marriage culture. The push to redefine marriage was brought to us. We don't know a single person involved in this effort who wouldn't rather focus on something else. But now that this is the live debate, we can't ignore it, for its outcome will have wider effects on the marriage culture that really is our main concern.

Long before the debate over same-sex marriage, a "marriage movement" was launched to explain why marriage was good for husbands and wives faithful to its demands, for their children, and for society more broadly.

Prominent articles, such as "Dan Quayle Was Right," Barbara Dafoe Whitehead's cover story for The Atlantic in 1993, tallied the high social costs of family fragmentation. The next decade saw the emergence of organizations such as Mike and Harriet McManus's Marriage Savers and policies such as the Bush administration's Healthy Marriage Initiative. The targets of these and countless other initiatives were high divorce and cohabitation rates and the rising birth rate among unmarried women. Same-sex relationships weren't on anyone's radar.

It was in this marriage movement that Maggie Gallagher, today's leading opponent of redefining marriage, was active throughout the 1980s and '90s. She wrote books documenting the sexual revolution's damage to "family, marriage, and sex" and making "the case for marriage" as a better arrangement for couples than cohabitation. One of us (RPG) joined her in the '80s after witnessing the havoc wrought by the collapsing marriage culture in his native Appalachia. (The other two of us were busy gestating or learning to read.) None of this was about gay anything.

Though the Defense of Marriage Act was passed in 1996, the question of whether to redefine marriage to eliminate sexual complementarity didn't take center stage until 2003, when the Massachusetts Supreme Court created a constitutional right to recognition of same-sex partnerships as marriages. By then, the marriage movement's leaders had no choice. They had to decide: Would recognizing same-sex relationships as marriages strengthen the marriage culture or further weaken it?

They concluded that same-sex marriage was not ultimately about expanding the pool of American couples eligible to marry. It was about cementing a new idea of marriage into the law -- the very idea whose baleful effects they had spent years fighting. That idea, that romantic and emotional union is all that makes a marriage, could not explain (as anything other than sentiment or personal preference) or support the stabilizing norms of permanence, monogamy, and sexual exclusivity that make marriage fitting for family life. It could only weaken them.

Indeed, it had already begun to do so. Disastrous policies such as no-fault divorce were motivated by the idea that a marriage is made by romantic attachment and satisfaction -- and comes undone when these fade. The marriage movement's leaders knew that to keep any footing for rebuilding the marriage culture, they had to fight the formal and final redefinition of marriage as essentially romantic companionship.

Why worry so much about policy?

Some think supporters of marriage should focus less on politics and more on civil society. This is a false and self-defeating dichotomy. We should focus both on politics and on culture, because each can only reinforce -- or undermine -- the other. Indeed, they are not entirely separate things.

Over time the law shapes what people think marriage is and requires, which in turn affects how people act toward and within marriage -- just think of the effects of no-fault divorce laws. The effects of redefining marriage to exclude sexual complementarity will likely be multiplied by anti-discrimination laws requiring the compliance of unwilling third parties and by changes in public-school curricula. Political and cultural efforts simply can't be separated. They are two fronts in the same battle to provide the space, motivation, and social support for couples to live according to a true ideal of marriage. Indeed, in some ways they aren't separate fronts at all: Law, policy, and politics are themselves part of culture.

How much does such social regulation matter? History is our lab, and the results are clear. Every political community that has lasted long enough to leave a trace of itself has regulated male-female sexual relationships. Why? These alone produce new human beings -- highly dependent little creatures who have the best chance of reaching physical, moral, and cultural maturity and of contributing to the community when reared by their own mothers and fathers in the context of marriage. But family stability doesn't happen by chance. It requires a strong marriage culture: norms and subtle influences designed to guide people's choices toward their own long-term interests and the common good.

Indeed, justice demands as much. By encouraging marital stability, the state vindicates a right -- that of a child to know the committed love of his own mother and father for him and for each other. And it limits the impact of negative externalities on innocent parties, because failed marriages and out-of-wedlock births burden us all with a train of social pathologies and a greater demand for policing and state-provided social services. The research of sociologists David Popenoe and Alan Wolfe on Scandinavian countries shows that as marriage culture declines, the size and scope of state power and spending grow. Libertarians, please take note.

A study by the left-leaning Brookings Institution finds that $229 billion in welfare spending between 1970 and 1996 can be attributed to the breakdown of the marriage culture and the resulting exacerbation of social ills: teen pregnancy, poverty, crime, drug abuse, and health problems. A 2008 study found that divorce and unwed childbearing cost taxpayers $112 billion each year.

Government is leaner and more effective when it supports marital norms than when it tries to pick up the pieces from a shattered marriage culture. And it can support these norms without banning anything. Libertarians and social conservatives should be allies on marriage.

Why wouldn't you want to recognize committed, monogamous same-sex relationships?

Some argue that marriage will civilize and stabilize same-sex relationships. But there is nothing magical about the word "marriage." It does not by itself promote marital norms no matter where or how we apply it. Rather, marital norms are promoted by marriage laws that embody and encourage a vision of marriage that makes sense of the norms as a coherent whole.

Marital norms make no sense, as a principled matter, if marriage is just whatever same- and opposite-sex couples can have in common -- namely, intense emotional regard. There is no reason of principle that emotional union should be permanent. Or limited to two persons rather than larger ensembles. Or sexual, much less sexually exclusive (as opposed to "open"). Or inherently oriented to family life and shaped by its demands. (Couples may live out these norms where temperament or taste motivates them, but there is no reason of principle for them to do so, and no basis for using the law to encourage them to do so.)

In other words, if sexual complementarity is optional for marriage, present only where preferred, then so is almost every other norm that sets marriage apart. Though some same-sex marriage supporters would disagree, this point can be established by reason, and is increasingly confirmed by the rhetoric and arguments used in the campaign to redefine marriage, by the policies that many of its leaders are increasingly led to embrace, and even by preliminary social science.

Thus, in their statement "Beyond Same-Sex Marriage," more than 300 "LGBT and allied" scholars and advocates -- including such prominent figures as Gloria Steinem and NYU law professor Kenji Yoshino -- call for legally recognizing sexual relationships involving more than two partners. Professor Elizabeth Brake, of the University of Calgary, argues that justice requires using legal recognition to correct for "past discrimination against . . . polygamists and care networks."

What about the connection to family life? Andrew Sullivan says that marriage has become "primarily a way in which two adults affirm their emotional commitment to one another." E. J. Graff celebrates the fact that recognizing same-sex relationships as marriages would change the "institution's message" so that it would "ever after stand for sexual choice, for cutting the link between sex and diapers."

And exclusivity? Mr. Sullivan, who has extolled the "spirituality" of "anonymous sex," thinks that the "openness" of same-sex relationships could enhance the bonds of husbands and wives by promoting "flexibility" -- euphemisms for sexual infidelity. Dan Savage argues for the same in a New York Times Magazine article titled "Married, with Infidelities." A piece in The Advocate, a gay-interest newsmagazine, supports our point still more candidly:

Anti-equality right-wingers have long insisted that allowing gays to marry will destroy the sanctity of "traditional marriage." . . . What if -- for once -- the sanctimonious crazies are right? Could the gay male tradition of open relationships actually alter marriage as we know it? And would that be such a bad thing?

These are not our words, but those of leading supporters of same-sex marriage. We could provide many, many more examples. If you believe in permanence and exclusivity but would redefine marriage, take note.

In fact, some have embraced the goal of weakening the institution of marriage in these very terms. Former president George W. Bush is correct, says Victoria Brownworth, "when he states that allowing same-sex couples to marry will weaken the institution of marriage. . . . It most certainly will do so, and that will make marriage a far better concept than it previously has been." Michelangelo Signorile urges those in same-sex relationships to "fight for same-sex marriage and its benefits and then, once granted, redefine the institution of marriage completely."

These ideas play out in policy. Since countries have begun recognizing same-sex relationships, governments have seen challenges to nearly every other traditional norm: Mexico City considered expressly temporary marriage licenses. Equality-based proposals to decriminalize or recognize polygamy have arisen in Canada and elsewhere. A public notary in Brazil recognized a three-person partnership (a "triad" or "throuple") as a civil union, saying that the redefinition of marriage required it: "What we considered a family before isn't necessarily what we would consider a family today."

Preliminary social science confirms that marital norms would be weakened by the establishment of same-sex marriage. The New York Times recently reported on a study finding that exclusivity was not the norm among gay partners: "With straight people, it's called affairs or cheating," said Colleen Hoff, the study's principal investigator, "but with gay people it does not have such negative connotations." In fact, several studies suggest that there is either no difference between exclusive and open same-sex male relationships or greater stability in the open ones. By contrast, 99 percent of opposite-sex couples demand of each other and anticipate sexual exclusivity in their marriage, and violations of it are, in one study's words, "the leading cause of divorce across 160 cultures and are one of the most frequent reasons that couples seek marital therapy."

All the evidence suggests that same-sex marriage simply cannot generate social norms of the sort traditionally associated with marriage. That is because such norms make less sense as general requirements for same-sex relationships than they do for truly conjugal unions, as many LGBT scholars and activists concede.

How would recognizing same-sex relationships as marriages hurt marriage?

Recognizing same-sex relationships as marriages requires replacing one basic vision of what marriage is (in our law, and hence in our mores, and hence in practice) with another vision of marriage. The new vision is one that equates marriage with the much broader category of companionship. Companionate bonds have great personal value, but they can't ground in a principled way the norms that set marriage apart.

To the extent that marriage is misunderstood, it will be harder to see the point of its norms, to live by them, and to encourage their strict observance. And this, besides making any remaining restrictions on marriage arbitrary, will damage the many cultural and political goods that first got the state involved in marriage. Here is a summary of those goods.

Real marital fulfillment. No one acts in a vacuum. We all take cues from cultural norms, many of which are shaped by the law. To form a true marriage, one must freely choose it. And to choose marriage, one must have at least a rough idea of what it is. The revisionist view would harm people (especially future generations) by distorting their idea of what marriage is. It would teach that marriage is essentially about emotional fulfillment and cohabitation, without any inherent connections to bodily union or procreation and family life. As individuals internalized this view, their ability to realize genuine marital union would diminish. This would be bad in itself, since marital union is good in itself. It would be the subtlest but also the primary harm of redefining marriage; other harms include the effects of misconstruing marriage.

Spousal well-being. Marriage tends to make spouses healthier, happier, and wealthier. But what does this is marriage, especially through its distinctive norms of permanence, exclusivity, and orientation to family life. As the state's redefinition of marriage makes these norms harder to understand, justify, and live by, spouses will enjoy less marital stability and less of the psychological and material advantages that flow from it.

Children's well-being. If same-sex relationships are recognized, not only will the stabilizing norms of marriage be undermined, but the notion that men and women tend to bring different gifts to parenting will not be reinforced by any civil institution. Redefining marriage would soften the social pressures and lower the incentives -- already diminished these past few decades -- for husbands to stay with their wives and children and for men and women to marry before having children. All this would harm children's development into happy, productive, upright adults.

Friendship. Misunderstandings about marriage will speed our society's drought of deep friendship, with special harm to the unmarried. The state will have defined marriage mainly by degree or intensity -- as offering the most of what makes any relationship valuable: shared emotion and experience. It thus will become less acceptable to seek (and harder to find) emotional and spiritual intimacy in nonmarital friendships. Instead of being seen as different from marriage and therefore distinctively appealing, they will be regarded simply as less. Only the conjugal view, which gives marriage a definite orientation to bodily union and family life, preserves a horizon richly populated with many types of association and affection, each with its own scale of depth and specific forms of presence and care.

Religious liberty. As the conjugal view of marriage comes to be seen as irrational ("bigoted"), freedom to express and live by it will be curbed. Several states already have forced Catholic Charities to choose between giving up its adoption services and placing children with same-sex partners, against Catholic principles. Some defenders of marriage have been fired or denied employment or educational and career opportunities for publicizing their views. If marriage is redefined, believing what virtually every human society once believed about marriage -- that it is a male-female union -- will be seen increasingly as a malicious prejudice, to be driven to the margins of culture. The consequences for observant Christians, Jews, Muslims, and others are becoming apparent.

Limited government. The state is (or should be) a supporting actor in our lives, not a protagonist. It exists to create the conditions under which individuals and our freely formed communities can thrive. The most important free community, on which all others depend, is the marriage-based family; and the conditions for its thriving include the accommodations and pressures that marriage law provides for couples to stay together. Redefining marriage will further erode marital norms, thrusting the state further into leading roles for which it is poorly suited: parent and discipliner to the orphaned, provider to the neglected, and arbiter of disputes over custody, paternity, and visitation. As the family weakens, our welfare and correctional bureaucracies grow.

Isn't the fight against redefining marriage a losing battle?

The simple answer is no. A careful look at the polls reveals complex and dynamic trends. But how those polls change will depend on human choice, not blind historical forces. The question is not what will happen, but what we should do.

Consider, first, the much-vaunted 2012 election results of marriage-related referenda. In Maine, Romney received 40 percent of the vote, and marriage 47 percent. In Maryland, it was Romney 37 percent, marriage 48 percent. In Minnesota, Romney 45 percent, marriage 48 percent. In Washington State, Romney 42 percent, marriage 47 percent. All this in a campaign in which proponents of redefinition had a four-to-one financial advantage and the backing of prominent figures: President Obama, Vice President Biden, governors, and a host of business, sports, and entertainment leaders. And in May, marriage won in a landslide, 61 percent to 39 percent, in a referendum in the swing state of North Carolina, a state Obama had carried in 2008 and lost fairly narrowly in 2012.

Do young people tend to favor redefining marriage? Yes, though not by the margins many assume. To the extent that young people lack a solid understanding of the nature and social purpose of marriage, we have reason to redouble efforts to reeducate a generation of heirs to the sexual revolution's ruins. We have no reason to give up on them, and no excuse for doing so.

Here we should take our cue from the pro-life movement, as one of us (RTA) argues in the Fall 2012 issue of the Human Life Review. In the years just after Roe, public opinion was breaking strongly for abortion. With each passing day another pro-life public figure -- Ted Kennedy, Jesse Jackson, Al Gore, Bill Clinton -- evolved to embrace abortion on demand. Elites ridiculed pro-lifers as being on the wrong side of history. The pro-life ranks were aging; their children, increasingly against them.

But courageous pro-lifers put their hands to the plow, and today we reap the fruits. Pro-lifers have decisively won the intellectual battle on the humanity of the unborn child. Most Americans now oppose most abortions, and despite politicians' blunders (as in the 2012 election), pro-life state laws are generally making great progress.

What happened? Besides the advent of the sonogram and other fortuitous factors, arguments, organizations, and strategies were developed. Similar work must now be done on the issue of marriage. Whatever the intelligentsia may say, only idleness can guarantee a political loss.

Taking this longer view, we like our chances. As young people settle down, marry, and have kids, they will develop greater appreciation for what makes a marriage, for the distinctiveness of husbands and wives, mothers and fathers. And if we are right about the likely harms of redefining marriage, then even a season of nationwide genderless marriage and its consequences would lead to a reassessment -- just as no-fault divorce spawned the marriage movement a generation ago.

Why limit freedom in the name of sectarian values?

If this debate indeed is about which of two visions of marriage to enshrine, then neutrality (or equality) by itself can't move us an inch toward requiring a redefinition of marriage. Neutrality can't favor enshrining one substantive moral vision of marriage over another. And it's clear that the revisionist view is indeed a substantive vision of marriage. The revisionist view still imposes some restrictions on what does and doesn't count as a marriage. For example, it excludes what Newsweek tells us are America's 500,000 multiple-partner (polyamorous) homes. Monogamy is just as much a standard as sexual complementarity.

But it isn't just marriage policy that can't be neutral. Settling other policies also requires controversial moral stances on issues where worldviews clash: affirmative action, abortion, assisted suicide, poverty relief, capital punishment, torture, and many more. That doesn't mean that the state must keep silent on these matters; it hardly can. Instead it must work to get them right -- which it's likeliest to do if citizens explain the reasons for their views with clarity and candor.

In fact, though, our view of marriage isn't ours in any sectarian sense. Something quite like it has been shared by the Jewish, Christian, and Muslim traditions; by ancient Greek and Roman thinkers untouched by these religions; and by various Enlightenment philosophers. It is affirmed by the common and the civil law, and by ancient Greek and Roman law. And far from having been intended to exclude same-sex relationships, it arose in many places, over several centuries, in which same-sex marriage was nowhere on the radar. Indeed, it arose in cultures that had no concept of sexual orientation, and in some that fully accepted homoeroticism and even took it for granted.

Still, redefining the historic conception of marriage to include same-sex relationships will undermine both the rationale behind civil marriage and (based on evidence only touched upon here) the practice of marriage, as well as all the crucial goods that depend on it.

Of course, support for marriage between a man and a woman is no excuse for animus against those with same-sex attractions, or for ignoring the needs of individuals who may never marry, for whatever reason. They are no less worthy than others of concern and respect, and public policy should do what is necessary and proper to help their lives go well. But the same diligent concern for the common good requires protecting and strengthening the marriage culture, by promoting the truth about marriage.

- Mr. Girgis is a Yale Law School student and a doctoral student in philosophy at Princeton. Mr. Anderson is the William E. Simon Fellow at the Heritage Foundation and a doctoral student in political science at Notre Dame. Mr. George is a visiting professor at Harvard Law School and the McCormick Professor of Jurisprudence at Princeton. For more of their work on marriage, see http://whatismarriagebook.com/.