Marriage is based on the truth that men and women are complementary, the biological fact that reproduction depends on a man and a woman, and the reality that children need a mother and a father. Redefining marriage does not simply expand the existing understanding of marriage; it rejects these truths. Marriage is society’s least restrictive means of ensuring the well-being of children. By encouraging the norms of marriage—monogamy, sexual exclusivity, and permanence—the state strengthens civil society and reduces its own role. The future of this country depends on the future of marriage. The future of marriage depends on citizens understanding what it is and why it matters and demanding that government policies support, not undermine, true marriage.

Marriage exists to bring a man and a woman together as husband and wife to be father and mother to any children their union produces. It is based on the anthropological truth that men and women are different and complementary, the biological fact that reproduction depends on a man and a woman, and the social reality that children need both a mother and a father. Marriage predates government. It is the fundamental building block of all human civilization. Marriage has public purposes that transcend its private purposes. This is why 41 states, with good reason, affirm that marriage is between a man and a woman. 

Government recognizes marriage because it is an institution that benefits society in a way that no other relationship does. Marriage is society’s least restrictive means of ensuring the well-being of children. State recognition of marriage protects children by encouraging men and women to commit to each other and take responsibility for their children. While respecting everyone’s liberty, government rightly recognizes, protects, and promotes marriage as the ideal institution for childbearing and childrearing.

At its most basic level, marriage is about attaching a man and a woman to each other as husband and wife to be father and mother to any children their sexual union produces... 

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 a husband and wife make marital love also makes new life, so marriage itself is inherently extended and enriched by family life and calls for all-encompassing commitment that is permanent and exclusive. In short, marriage unites a man and a woman holistically—emotionally and bodily, in acts of conjugal love and in the children such love brings forth—for the whole of life.[4] 

Just as the complementarity of a man and a woman is important for the type of union they can form, so too is it important for how they raise children. There is no such thing as “parenting.” There is mothering, and there is fathering, and children do best with both. 

Marriage is the fundamental building block of all human civilization. The government does not create marriage. Marriage is a natural institution that predates government. Society as a whole, not merely any given set of spouses, benefits from marriage. This is because marriage helps to channel procreative love into a stable institution that provides for the orderly bearing and rearing of the next generation.

Virtually every political community has regulated male–female sexual relationships. This is not because government cares about romance as such. Government recognizes 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 to which mothers and fathers bring unique gifts. Unless children mature, they never will become healthy, upright, productive members of society. Marriage exists to make men and women responsible to each other and to any children that they might have.

Redefining marriage would further disconnect childbearing from marriage. That would hurt children, especially the most vulnerable. It would deny as a matter of policy the ideal that children need a mother and a father. Traditional marriage laws reinforce the idea that a married mother and father is the most appropriate environment for rearing children, as the best available social science suggests. 

Recognizing same-sex relationships as marriages would legally abolish that ideal. It would deny the significance of both mothering and fathering to children: that boys and girls tend to benefit from fathers and mothers in different ways. 

Redefining marriage does not simply expand the existing understanding of marriage. It rejects the truth that marriage is based on the complementarity of man and woman, the biological fact that reproduction depends on a man and a woman, and the social reality that children need a mother and a father. 

Redefining marriage to include same-sex relationships is not ultimately about expanding the pool of people who are eligible to marry. Redefining marriage is about cementing a new idea of marriage in the law—an idea whose baleful effects conservatives have fought for years.

Redefining marriage marginalizes those with traditional views and leads to the erosion of religious liberty. The law and culture will seek to eradicate such views through economic, social, and legal pressure. If marriage is redefined, believing what virtually every human society once believed about marriage—a union of a man and woman ordered to procreation and family life—would be seen increasingly as a malicious prejudice to be driven to the margins of culture.

The future of this country depends on the future of marriage, and the future of marriage depends on citizens understanding what it is and why it matters and demanding that government policies support, not undermine, true marriage. 

Some might appeal to historical inevitability as a reason to avoid answering the question of what marriage is—as if it were an already moot question. However, changes in public opinion are driven by human choice, not by blind historical forces. The question is not what will happen, but what we should do.