Cohabitation is sparking conversation among couples after a New York Times article alleged that living together before marriage could bode poorly for a couple’s happily-ever-after prospects. Psychologist Meg Jay wrote about a nationwide survey conducted by the National Marriage Project that confirmed what she was seeing in her practice: That couples who live together before marriage are more likely to be dissatisfied by that marriage, and divorce.

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The article came days after one of the world’s most famous cohabitating couples — Brad Pitt and Angelina Jolie — decided to make it legal, announcing their engagement. Pitt and Jolie are examples of a trend from another recent study, which suggests that more children are being born to cohabitating parents. The Times story about cohabitation stayed on the most-emailed list all weekend, perhaps fueled by passive-aggressive forwards of the story from couples and singles, speculated Gawker.

There are a number of reasons that cohabitation is on the rise, according to the Times article: Better access to birth control, decreased stigma, and (especially these days) economic forces have made it easier for couples to shack up. Many couples also view living together as a tryout for marriage, rather than a step towards marriage. Jay says that when couples move in together, the “setup costs” — what you’ve invested in the relationship — make you more likely to stay, even if you aren’t a perfect match.

Jay is essentially telling couples what advice columnist Carolyn Hax has been saying for years: That when it comes to cohabitation, inertia is a powerful force. Hax’s advice is consistent: Move in together when you don’t think you’ll ever want to move out, but never before. Here’s what she has to say about cohabitation:

• “It’s a good idea to live together when you both think it’s a good idea to live together, and no sooner.” (Dec. 24, 2011)

• “Moving in with someone does have mistakes and bad outcomes associated with it, yes, but so does marriage. So does breaking up. So, with moving in vs. marriage — and with any other big decision, in fact — all you can do is be honest with yourself about your situation, make sure you’re informed, and resist the temptation to minimize the doubts that matter or hide behind the ones that don’t.” (Dec. 24, 2011)

• “Before you move in, inertia keeps you apart. After you move in, inertia keeps you together. To me, at least, it makes sense that the bond you create by overcoming inertia is going to be stronger than the one inertia creates. Too many people feel inclined to break up but don’t because the thought of it all is too daunting.” (March 20, 2012)

• “My general advice is that you're ready to move in with someone when you fully and mutually intend to spend the rest of your life with that person. That's not a guarantee you -will- spend the rest of your life with the person, nothing is, but it will at least (if you're being honest with yourself) hold you back from moving in because you're in love and excited to set up and share a home with someone. That pull is hard to resist, but it's well worth resisting.” (Feb. 11, 2011)