This week’s Ricochet posts on marriage have made a sustained argument about what marriage is and why marriage matters. For a more detailed treatment of these issues, look to my new book, co-authored with Sherif Girgis and Robert P. George, What Is Marriage? Man and Woman: A Defense.

Monday’s post pointed out that long before there was a debate about same-sex marriage, there was a debate about marriage. It launched a “marriage movement,” to explain why marriage was good for the men and women who were faithful to its responsibilities, and for the children they reared. Over the last decade a new question emerged: What does society have to lose by redefining marriage as we’ve always known it?

Answering that question must begin with a clear idea of what marriage is. Tuesday’s post explained that marriage is a uniquely comprehensive union. It involves a union of hearts and minds; but also—and distinctively—a bodily union made possible by sexual complementarity. As the act by which spouses make marital love also makes new life, so marriage itself is inherently extended and enriched by family life and calls for similarly all-encompassing commitment: permanent and exclusive. In short, marriage unites a man and woman holistically—emotionally and bodily, in acts of conjugal love and in the children such love brings forth—for the whole of life.

If this is what marriage is, why does the government care? Wednesday’s post explained the many ways in which marriage contributes to the public good. Government cares about male-female sexual relationships because these alone produce new human beings. For highly dependent infants, there is no path to physical, moral, and cultural maturity—no path to personal responsibility—without a long and delicate process of ongoing care and supervision. Unless children do mature, they never will become healthy, upright, productive members of society. Marriage exists to make men and women responsible to each other and any children they might have.

Thursday’s post documented statements by many leaders of the effort to redefine marriage that show no interest in retaining marital norms—in fact, quite the opposite. Redefining marriage to abandon the norm of male-female sexual complementarity also would make other essential characteristics—such as monogamy, exclusivity and permanency—optional. This is increasingly confirmed by the rhetoric and arguments of those who would redefine marriage, and by the policies that their more candid leaders increasingly embrace.

The most interesting—and revealing—comments on this week’s posts have been those that said marriage is simply whatever sort of interpersonal relationship consenting adults—be they two or 10 in number—want it to be; sexual or platonic, sexually exclusive or open, temporary or permanent.

That idea sounds like the abolition of marriage. Marriage is left with no essential features, no fixed core as a social reality—it is simply whatever consenting adults want it to be.

If so, how can redefining marriage for public purposes to include same-sex relationships be a demand of justice? A matter of basic fairness and equality? From the wide variety of interpersonal consensual relationships that adults can form, why should the state pick out same-sex ones?

Indeed, some of those who posted comments saw this logic, and thinking that marriage has no form and serves no social purpose, they concluded that the government should get out of the marriage business.

If so, how will society protect the needs of children—the prime victim of our non-marital sexual culture—without government growing more intrusive and more expensive?

Marriage benefits everyone, because separating the bearing and rearing of children from marriage burdens innocent bystanders: not just children, but the whole community. It’s the community that often must step in to provide (more or less directly) for their wellbeing and upbringing. A child born and raised outside marriage is six times more likely to experience poverty than a child in an intact family—and therefore welfare expenditures grow. So by encouraging the norms of marriage—monogamy, sexual exclusivity and permanence—the state strengthens civil society and reduces its own role.

But marital norms make no sense—as matters of principle—if marriage is redefined. There is no reason of principle why emotional union should be permanent. Or limited to two persons, rather than larger ensembles. Or sexual, much less sexually exclusive. Or inherently oriented to family life and shaped by its demands.

If marriage isn’t founded on a comprehensive union made possible by the sexual complementarity of a man and a woman, then why can’t it occur among more than two people? If marital union isn’t founded on such sexual acts, then why ought it be sexually exclusive? If marriage isn’t a comprehensive union and has no intrinsic connection to children, then why ought it be permanent?

This isn’t to say that couples couldn’t decide to live out these norms where temperament or taste so motivated them; but that there is no reason of principle to demand it of them. So legally enshrining this alternate view of marriage would undermine the norms whose link to the common good justifies state action in the first place.

This highlights the central questions in this debate: what marriage is and why the state recognizes it. It’s not that the state shouldn’t achieve its basic purpose while obscuring what marriage is. Rather, it can’t. Only when policy gets the nature of marriage right do we reap the civil society benefits of recognizing marriage.

The future of our country, then, relies upon the future of marriage. The future of marriage depends on citizens’ understanding of what it is and why it matters—and demanding that government policies support, not undermine, true marriage.