For decades now, a dispute has raged between liberals and conservatives about whether the decline in marriage is a cause or a consequence of economic problems for the American working class. Conservatives like David Brooks believe a crisis of morals is driving poverty up. Liberals like Paul Krugman counter that this is backward, and it's working-class economic decline that's driving the crisis of values.

They're both wrong — and not just about their explanations for the problem. They're wrong about the idea that there is a problem to explain.

This is clarified by looking at two pieces of data. One is international comparisons of marriage trends; the other is actual outcomes for American children. Globally, we don't see low marriage rates leading to widespread poverty, nor do we see poorer countries exhibiting lower marriage rates. Instead, the countries with higher rates of out-of-wedlock births are generally the ones with the most fortunate working classes, while countries that are considerably poorer than the United States have stronger marriage norms.

But the decline in marriage is no black fly in the chardonnay, either. It's true there is a lot of very persuasive observational data to indicate that children raised by stable, loving couples end up better off than children whose family lives are disrupted by divorce or breakups. But what we don't see is the aggregate increase in children borne by unmarried women leading to bad aggregate outcomes. Instead, the current generation of teenagers is the best-behaved on record. Young people are doing less drugs, having fewer teen pregnancies, and even doing better at meeting federal exercise guidelines. The high school graduation rate is at an all-time high, and so is the share of the population with a college degree.

How marriage fights poverty

One thing conservatives are absolutely right about is that marriage is an extremely powerful tool in the war on poverty. What conservatives are less good at is explaining how and why this works. Marriage's potency as an anti-poverty tool is largely a mechanical result of how poverty is defined in the United States, paired with the existence of basic household economies of scale.

A woman working 40 hours a week, 50 weeks a year, at the federal minimum wage of $7.25 will find herself earning $14,500 a year — well above the federal poverty level. If she has a kid, her two-person household will slip below the poverty line — even if she's working the same hours. But if she marries another single mom with an identical job, their new four-person household makes $29,000 a year — and is no longer poor, according to the government. Indeed, they could even have a fifth child and still not be poor.

If every poor adult in America married another poor adult, in other words, we would see a significant drop in the poverty rate. Nobody's actual income would have increased, of course, but through the magic of statistics we would achieve a significant win in the war on poverty.

And of course, if every poor person in America were to fall in love with a quality partner and form a fulfilling lifelong partnership, that would be great news! Indeed, one is strongly inclined to say it would be great news for much deeper reasons than anything related to economics.

By the same token, however, passing a law saying every poor unmarried adult is going to get flogged on Valentine's Day would almost certainly reduce poverty. What it wouldn't do is actually make people better off. What would happen is some single people would be flogged (bad) and some newly married people would be unhappy in their relationships (also bad).

A roommate could be as good as a husband

Some of this goes to show there's a level of arbitrariness to our definitions of household income and poverty. But it really is the case that bigger households have economic advantages. It does not cost twice as much to heat a home for two. Nor do you need two times the cable subscriptions. Bulk purchases of food (or, for that matter, toilet paper) are more efficient than shopping for one. And of course, a multi-person household can share things like kitchen space and bathrooms.

This is why when I first moved to Washington, DC, and didn't make much money I lived with roommates.

But eventually I started making more money and moved out of the group house I was renting to a shiny new one-bedroom condo. Because my monthly mortgage payments were substantially higher than my share of the old group house rent, I ended up with slightly less disposable income than I had before the raise. But that's not a wildly unusual situation for an urban professional who's getting a bit long in the tooth. You decide you want to live alone, and you're willing to endure a moderate financial sacrifice for the sake of personal space.

The relationship between marriage and economic prosperity should be seen in somewhat similar terms. In places where women have very few economic opportunities, they can't afford to be too choosy about marriage partners. Where women are more empowered, they become choosier. At times, this greater choosiness leaves them with less money than they would otherwise have. But that's the point. It's precisely because women are more empowered that they can afford to trade off economic security for other benefits.

Marriage is getting better

Unlike the conservative or liberal pessimist narratives, the optimist narrative fits a broad range of data. Marriage has declined more in the Nordic countries than in the United States, but more in the United States than Portugal, because the USA is between the Nordics and Portugal in terms of economic security for working-class women. And marriage rates are lower almost everywhere in 2015 than they were in 1915 because working-class women have more economic opportunity today in virtually every country than they did 100 years ago.

Marriage has long been, at least in part, a deeply gendered economic arrangement, so it's natural that growing economic opportunities for women would transform the meaning of marriage. In particular, it has made women choosier about their partners. That led to a surge in divorces in the 1970s, followed by a slow and steady decline in the divorce rate ever since 1981 or so.

Among college graduates, marriage has been re-founded on a new basis. As Betsey Stevenson and Justin Wolfers put it, we have gone from shared production to shared consumption and formed more egalitarian partnerships based on common preferences rather than a swap of housework for rent money. This new model of partnerships has thus far not taken root as strongly in working-class relationships. That's unfortunate. But it's a mistake to believe women are making themselves worse off than their next actually available alternative. As women have become more empowered, they have gotten pickier. That means more single women, and a higher quality of relationship for the non-single.

None of this is to deny either the conservative premise that many people would be better off in stable, loving relationships or the liberal premise that more and better employment opportunities for working-class men could make such relationships more likely.

But to explain a social crisis, you first have to establish that a crisis is occurring. There is no major dimension on which American children are doing worse in 2015 than they were in 1975. That should be a huge giveaway that the decline of marriage is a consequence of something good — prosperity, especially for women — rather than a cause or a consequence of something bad.