Rightly understood, marriage is all about permanence. In a world of transitory experiences, events, and commitments, marriage is intransigent. It simply is what it is — a permanent commitment made by a man and a woman who commit themselves to live faithfully unto one another until the parting of death.

That is what makes marriage what it is. The logic of marriage is easy to understand and difficult to subvert, which is one reason the institution has survived over so many millennia. Marriage lasts because of its fundamental status. It is literally what a healthy and functioning society cannot survive without.

And yet, modernity can be seen as one long attempt to subvert the permanent — including marriage. The modern age has brought the rise of individual autonomy, the collection of populations in cities, the weakening of family commitments, the waning of faith, the routinization of divorce, and a host of other developments that subvert marriage and the commitment it requires.

Added to this list is the phenomenon of cohabitation. The twentieth century saw the phenomenon of cohabitation become the expectation among many, if not most, young adults. But the end of the century, the progression of intimacy (including sexual intimacy) was likely to follow a line from “hooking up” to cohabiting.

A new study conducted by the National Center for Health Statistics suggests two very important findings: First, that cohabiting is now the norm for younger adults. Second, cohabiting makes divorce more likely after eventual marriage.

“Cohabitation is increasingly becoming the first co-residential union formed among young adults,” states the report. The facts seem daunting. The percentage of women in their 30s who report having cohabited is over 60 percent — doubled over the last fifteen years.

Reporting in The New York Times, Sam Roberts documents the rise of cohabitation among the young. He cites Pamela J. Smock of the University of Michigan’s Population Studies Center. “From the perspective of many young adults, marrying without living together first seems quite foolish,” she explains.

That perfectly captures the new logic — that it would be foolish to marry without first cohabiting. How can you know if you are really meant for each other? How can you measure compatibility without the experience of living together?

That logic makes perfect sense in a society that is increasingly sexualized, secularized, and “liberated” from the expectations of the past.

Reacting to the research findings, Professor Kelly A. Musick of Cornell University asserted, “The figures suggest to me that cohabitation is still a pathway to marriage for many college graduates, while it may be an end in itself for many less educated women.”  The study report affirmed her assessment: “Cohabitation is increasingly becoming the first co-residential union formed among young adults . . . . As a result of the growing prevalence of cohabitation, the number of children born to unmarried cohabiting parents has also increased.”

But, as this new report suggests, cohabiting before marriage does not lead to a stronger and more permanent union. Instead, the experience of cohabiting weakens the union. As Roberts reports: “The likelihood that a marriage would last for a decade or more decreased by six percentage points if the couple had cohabited first, the study found.”

Pamela Smock argues that the research will fall on deaf ears. “Just because some academic studies have shown that living together may increase the chance of divorce somewhat, young adults themselves don’t believe that.”

That may be true, and it surely captures the spirit of the age. The experience of cohabiting just makes sense to many young adults. Their logic is that marriage is what happens after a relationship becomes sexually intimate and is found to be adequately fulfilling — not before.

They do not know that what they are actually doing is undoing marriage. They miss the central logic of marriage as an institution of permanence. They miss the essential wisdom of marriage — that the commitment must come before the intimacy, that the vows must come before the shared living, that the wisdom of marriage is its permanence before its experience.

Cohabitation weakens marriage — even a cohabiting couple’s eventual marriage — because a temporary and transitory commitment always weakens a permanent commitment. Having lived together with the open possibility of parting, that possibility always remains, and never leaves.

This research might not alter the plans of many young couples, who are not likely to read, much less be advised by such research. But it does affirm what makes marriage what it is, and what weakens and destroys marriage as an institution.

From a Christian perspective there is more, of course. We are reminded of marriage as God’s gift and expectation, and of the divine goodness of it. We are also reminded that it is our Creator, and not we ourselves, who knows that we need permanence before experience. We need marriage.