For most couples, getting their vehicle stuck in the mud en route to their nuptials might have caused a wave of panic. But not for David Letterman and his girlfriend Regina Lasko on their wedding day last Wednesday in Choteau, Mont.
What was a few hours when they had waited more than 20 years to tie the knot?
Mr. Letterman is one of many snail-paced grooms making solemn vows to their long-time girlfriends. In December, Woody Harrelson and his girlfriend Laura Louie tied the knot after two decades and three children together. Harrison Ford and Calista Flockhart were reportedly engaged this week after eight years together - a relatively feverish courtship by comparison.
Now that common-law arrangements have gone mainstream, expert observers say that cases like Mr. Letterman's are indeed on the rise - and shaking up what researchers know about the patterns of common-law relationships.
Most common-law relationships take two forms, says Christopher Thomson, who teaches the philosophy of love and sex at Ryerson University's G. Raymond Chang School of Continuing Education. They are either short-term preludes to marriage or they function as, essentially, long-term substitutes for it. But with more couples choosing common-law status, the lines are beginning to blur.
Stephanie Coontz, author of Marriage, A History, says that while common-law couples enjoy most of the same legal advantages as married couples in North America, the social pressure to marry remains strong - except in Quebec.
"One of the peculiarities of American history - and in the English-speaking world in general - is this idea that we will respect marriage, but we do not have long-term expectations of other relationships. ... We put everything in the basket of marriage," says Prof. Coontz, a professor of history and family studies at the Evergreen State College in Olympia, Wash.
As Dr. Thomson puts it: "You can only listen to people for so long politely ask you, year, after year, 'When are you finally going to get married?'
"Even though the pressure is kind and subtle, it's there and it's persistent."
And many couples willingly admit that acquiescing feels, well, grown-up. Toronto writer and television producer Liz Hodgson happily embraced tradition three years ago when she married her partner of 12 years. Living together as common-law spouses as they entered their 40s was "feeling a tad bohemian for my taste," she says.
For some, having children intensifies the urge. As actress Julianne Moore told the parenting website Babble.com this week, she once told Mr. Letterman her own reasoning for getting married to Bart Freundlich when their children were 5 and 1.
"I said, 'Well, one kid it seems like it's okay not to be married, and two kids it just starts to seem sloppy.' "
That doesn't mean a late-term marriage is merely about sober responsibility, say Matt Titus and Tamsen Fadal, the authors of Why Hasn't He Proposed? Go From the First Date to Setting the Date.
"It can give the relationship a bit of a fuel injection," Mr. Titus says.
Still, those who decide to marry well into a relationship admit they have to overcome some of their own prejudices and fears. Ms. Hodgson, for instance, found herself confronting her own lapsed liberal-feminist views on marriage. For many men, it means jettisoning an aversion to commitment.
Mr. Letterman admitted as much when discussing his decision: "I had avoided getting married pretty good for, like, 23 years, and I ... secretly felt that men who were married admired me ... like I was last of the real gunslingers."
But can reformed gunslingers be happy in marriage?
Until recently, research suggested that those who lived together before marriage had a higher rate of divorce, but with a rise in co-habitation, the opposite is now true. The only exception? If partners are "on different pages" in their attitudes toward marriage.
"If you slide into a marriage to please one partner, your risk of divorce rises," Prof. Coontz says. "But you cannot accuse [a couple that]has lived together 23 years of sliding into marriage."