Rachel Lu, a teacher of philosophy at the University of St. Thomas, described this experience from her classroom:

For several semesters running, I've encouraged the students of my introductory ethics course to discuss the issue [of what exactly is marriage], and it’s striking how quickly they give up. The problem isn’t that they disagree. They just frankly don’t know.

My students are pretty quick to agree that marriage must be a contract of some kind. When we try to spell out the terms, though, they can’t come up with a single thing that definitely seems to belong on the list. Should spouses live together? It’s generally a good idea, but you know, depends on circumstances. Should they have children, or try? Totally optional. How about sexual exclusivity? That’s probably a good idea, but ultimately up to the spouses themselves.

They end up concluding that marriage is a completely do-it-yourself sort of project. Spouses just have to talk things over and decide what they want their marriage to be. Here’s the thing, though. If our young people (so, the people who should be getting married in the foreseeable future) can’t say anything about what marriage actually is, then the concept is just meaningless. That should maybe worry you if you think that marriage has some significance to a healthy society.

"Progressive" forces in our society have worked to destroy the traditional concepts of marriage: that marriage is a contract between a man and a woman; that marriage is permanent and unbreakable except by gross misconduct; that marriage is the proper context for bearing and raising children; that sexual relations with parties outside of the marriage are immoral and intolerable; and so on. The new definition of marriage, per these forces, is much weaker: a ceremonial unity between any two consenting adults, prompted by "love," dissolvable once the "love" is gone. In this brave new world; marriage isn't even a contract: In most contracts, the person who breaches must make some kind of compensation to those who relied on his performance of the contract. But the "progressive" form of marriage permit people to dissolve the contract for any reason or no reason and never even offer an account of themselves.1

Under the new definition of marriage, billions of people in the history of the world who thought they were married were not. Most marriages have been arranged. Love may percolate later, but only as a result of marriage, not the reason for it.

Further, if love were the sine qua non of marriage, no “for better or for worse” promises would be needed at the altar. Vows aren’t meant to sustain love; they are meant to sustain the union when love wanes. A pledge keeps a family intact not for love, but for the sake of children.2

Ironically for those who promote same-sex marriage, society has already neutered marriage. If marriage is a ceremonial union, purposed in transient "love," that can dissolve once the "love" is gone, then why bother with the complications of the union in the first place?

Some might say we should completely deregulate relationships between adults. The only interest the state should have is in the protection of children. The state shouldn’t care at all about the relationship between the adults, only whether the child’s needs are being met.

But this is essentially what we are already doing with the children of unmarried parents. The outcomes for these children are not the sort of thing we would want to expand to the entire population. These children have poorer life chances in virtually every dimension we can measure, even taking into account their parents’ lower incomes. The fact that the children of unmarried mothers so often end up in the child welfare system tells us that their needs are not being met.3

My Definition of Marriage

My definition of marriage is as much theological as it is biological. At its root, it is the recognition that only one form of sex results in conception and the propagation of the species. But on a higher level, it is the recognition that sex is not just a bodily function but a profound act with consequences that are not just procreative and physiological but also spiritual.

Sex is the means by which the spiritual and procreative union between two people manifests itself in the physical realm and thus bears fruit. The sexual "union" of two men and the sexual "union" of two women cannot result in conception and does not carry the same risks as male-female coitus. Such "sex" is more correctly described as masturbation.

Genuine marriage bears tangible and intangible fruit. (Not necessarily children.) True marriage is never destructive. It feeds the participants and makes them healthier in all regards—physically, emotionally, and spiritually.