As Sherif Girgis, Robert P. George, and I argue in The Wall Street Journal, the future of marriage is the future of humanity.

Conservatives rightly uphold the institution of marriage between a man and a woman because marriage is the seedbed of society, the necessary precondition for limited self-government.

But not everyone sees it this way. With the Supreme Court expected to decide this week whether to hear challenges to traditional marriage laws, now is the time for citizens to think deeply about the nature and purpose of marriage.

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.

In the revisionist view of marriage, however, what sets marriage apart from other bonds is emotional intensity—what one philosopher refers to as your “number one person.” But nothing about emotional union requires it to be permanent. Or limited to two. Or sexual, much less sexually exclusive. Or inherently oriented to family life and shaped by its demands.

As a result, redefining marriage to include same-sex relationships would harm the common good as it obscures the true nature of marriage and thus weakens the marriage culture. Weakening marital norms would hurt children and spouses, especially the poorest among us.

Empty appeals to “equality” get us nowhere. As my co-authors and I argue:

Every marriage policy draws lines, leaving out some types of relationships. Equality forbids arbitrary line-drawing. But we cannot know which lines are arbitrary without answering two questions: What is marriage, and why does it matter for policy?

The conjugal and revisionist views are two rival answers; neither is morally neutral. Each is supported by some religious and secular worldviews but rejected by others.… So voters must decide: Which view is right?

The best philosophy, theology, sociology, and what G. K. Chesterton called the democracy of the dead—tradition—all suggest that the conjugal view is right.

As we argue in our new book What Is Marriage? Man and Woman: A Defense, marriage is a uniquely comprehensive union. It involves a union of hearts and minds but also a bodily union made possible by sexual complementarity. Marriage is inherently extended and enriched by procreation and family life and objectively calls for similarly all-encompassing commitment, norms of permanence, and exclusivity.

In the op-ed, we detail why conservatives would be ill-advised to abandon support for conjugal marriage even if it hadn’t won more support than Governor Mitt Romney in every state where marriage was on the ballot.

Read our WSJ article here; our book may be ordered here.