Editor’s note: This week the Democrats gather in Philadelphia to nominate a candidate for president and adopt a party platform. Given that there are no minority reports to the Democratic platform, it is likely that it will be adopted as-is this week. And so we can begin the comparison of the two major party platforms. For those who say there are no differences between the Republican and Democratic parties, just read the platforms side-by-side. In many instances, the differences are—as Donald Trump would say, yuuuge. But in one surprising instance, the two parties actually agree. This piece walks readers through one of the biggest contrasts, while an earlier piece by Elaine Kamarck detailed a striking similarity.

When it comes to Republicans and the environment, black is the new green. In addition to denouncing “radical environmentalists” and calling for dismantling the EPA, the platform adopted in Cleveland yesterday calls coal “abundant, clean, affordable, reliable domestic energy resource” and unequivocally opposes “any” carbon tax.

Meanwhile, Democrats are moving in the opposite direction. By the time the party’s draft 2016 platform emerged from the final regional committee meeting in Orlando, it contained a robust section on environmental issues in general and climate change in particular. One of the many amendments adopted in Orlando contains the following sentence: “Democrats believe that carbon dioxide, methane, and other greenhouse gases should be priced to reflect their negative externalities, and to accelerate the transition to a clean energy economy and help meet our climate goals.” In plain English, there should be what amounts to a tax (whatever it may be called) on the atmospheric emissions principally responsible for climate change, including but not limited to CO2.

As Brookings’ Adele Morris pointed out in a recent paper, this proposal raises a host of design issues, including determining initial price levels, payers, recipients, and uses of revenues raised. It would have to be squared with existing federal tax, climate, and energy policies as well as with climate initiatives at the state level.

But these devilish details should not obstruct the broader view: To the best of my knowledge, this is the first time that the platform of a major American political party has advocated taxing greenhouse gas emissions. Many economists, including some with a conservative orientation, will applaud this proposal. Many supporters and producers of fossils fuels will be dismayed.

It remains to be seen how the American people will respond. In a survey conducted in 2015 by Resources for the Future in partnership with Stanford University and the New York Times, 67 percent of the respondents endorsed requiring companies “to pay a tax to the government for every ton of greenhouse gases [they] put out,” with the proviso that all the revenue would be devoted to reducing the amount of income taxes that individuals pay. Previous surveys found similar sentiments: public support increases sharply when the greenhouse gas tax is explicitly revenue-neutral and declines sharply if it threatens an overall increase in individual taxes.

Once this plank of the Democratic platform becomes widely known, Republicans are likely to attack it as yet another example of Democrats’ propensity to raise taxes. The platform’s silence on the question of revenue-neutrality may add some credibility to this charge. Much will depend on the ability of the Democratic Party and its presidential nominee to clarify its proposal and to link it to goals the public endorses.

There is a marriage gap in America. This is not just a gap in choices and actions, but in norms and attitudes. Each generation is more liberal, on average, when it comes to issues like premarital relationships, same-sex marriage, and divorce. But generational averages can obscure other divides, including ideology—which in many cases is a more powerful factor.

Take opinions on the most important prerequisites for marriage, as explored in the American Family Survey conducted earlier this year by Deseret News and the Center for the Study of Elections and Democracy (disclosure: I am an adviser to the pollsters). There is widespread agreement that it is best to have a stable job and to have completed college before tying the knot. But there is less agreement in the 3,000-person survey on other questions, including premarital cohabitation.

In response to the question of whether it is “important to live with your future spouse before getting married,” a clear gap emerges between those who identify as Democrats and those who identify as Republicans. This gap trumps the generational one, with younger Republicans (under 40) more conservative than Democrats over the age of 40:

The importance of family stability for a child’s wellbeing and prospects is well-documented, not least in Isabel Sawhill’s book, Generation Unbound. The question is not whether stability matters, but how best to promote it. To the extent that biological parents stay together and provide a stable environment, it doesn’t much matter if they are married. For children living with both biological parents, there is no difference in outcomes between those being raised by a married couple compared to a cohabiting couple, according to research by Wendy Manning at Bowling Green State University.

But people who marry are much more likely to stay together:

Marriage, at least in America, does seem to act as an important commitment device, a “co-parenting” contract for the modern world, as I’ve argued in an essay for The Atlantic, “How to Save Marriage in America.”

Cohabitation can signal radically different situations. A couple who plan to live together for a couple of years, then marry, and then plan the timing of having children are very different from a couple who start living together, accidentally get pregnant, and then, perhaps somewhat reluctantly, get married.

There is some evidence that cohabitation is in fact becoming a more common bridge to marriage and commitment. First-time premarital cohabiting relationships are also lasting longer on average and increasingly turn into marriage: around seven in ten cohabiting couples are still together after three years, of whom four have married.

In the end what matters is planning, stability, and commitment. If cohabitation is a planned prelude to what some scholars have labeled “decisive marriages,” it seems likely to prove a helpful shift in social norms, by allowing couples to test life under the same roof before making a longer-term commitment. Sawhill’s distinction between “drifters” and “planners” in terms of pregnancy may also be useful when it comes to thinking about cohabitation, too.