The Sexual Revolution happened.

That is to say, starting in the 1960s, widespread cultural transformations combined with the invention of cheap, reliable birth control to bring about very significant changes in the way most people in the modern West approach sexuality, relationships, the family, childbearing, and so on. These changes have been manifold, they have been widespread, and they have been profound.

This is something that, as far as I can tell, no one on Planet Earth disputes. There is a dispute about what this tidal change continues to mean and where it is going, and about whether the effects of the Sexual Revolution have been good, bad, or a complex mix of the two.

But the Sexual Revolution happened. That much is indisputable.

I feel the need to point this out because there is a somewhat surreal debate going on about the state of marriage in America in the lower and middle classes. By now, progressives have grudgingly recognized that it is much, much better for children to be brought up in stable, two-parent households, a fact that is backed by overwhelming social science and psychological evidence. They have been dragged into sharing the conservative alarm that so many American children in the lower and middle classes are brought up in unstable families.

The degeneration of the family has been going on for decades, but it is now more prevalent than ever. It has potentially very far-reaching consequences in terms of social mobility, human capital formation, and poverty alleviation. And it is, quite simply, a massive impediment that prevents all of us from flourishing.

But while progressives agree that it is a worrisome trend, they disagree with conservatives about the causes, and what to do about it. Family breakdown among the lower and middle classes, many of them say, is a pure product of economics. The changes brought about by globalization — the end of stable union jobs, globalization and outsourcing, the shift to a services-based economy — have increased the stress on the working class and therefore made marriage harder. At bottom, the problem is that poor people don't have enough money, and that problem has a simple solution: The government should write people checks.

No one disputes that these economic trends have played some role in degrading the traditional family, and that there are appropriate public policy responses, including, yes, in some cases, redistribution. In fact, many of the conservatives who started this conversation stand out from other conservatives precisely because they favor a mix of responses that addresses both the economic and cultural roots of the problem, rather than focusing solely on culture.

But most progressives in this discussion are not arguing about the precise extent of the respective roles played by economics and culture, which would be a very productive discussion — they are simply denying that culture plays a role at all (in what amounts to one of the most emblematic examples of the Left's vulgar Marxism problem).

While some conservatives have shown superhuman patience — witness Ross Douthat's first of several very forbearing blog posts on this topic earlier this week — at some point someone has to say that the sky is blue and the Earth is round. To question whether the Sexual Revolution has had something to do with the decline of marriage is like wondering whether the French Revolution had anything to do with regicide.

Given that the family held up comparatively well during the Great Depression, and that today's lower class, while not doing great, is wealthy beyond the dreams of most people in the 18th century, to suggest that the biggest cultural trend in the 20th century has not affected marriage is prima facie absurd.

At some point, you start to feel like the poor man in Monty Python's "Dead Parrot Sketch" trying to convey his meaning. A change in how people approach sex, relationships, and family has changed how people approach sex, relationships, and family. After all, it's called the "Sexual Revolution," not the "Sexual Fad That Didn't Affect How People Live." That's what it means. That's what it is.

Again, none of this is to dispute that economics plays a role as well, and that there are appropriate policy responses. But to suggest that culture had no impact on culture is tantamount to saying that white is black, war is peace, and love is hate.