Anthropologists have a term for this racheting-up of opposition: schismogenesis. Gregory Bateson developed the word to describe mirroring interactions, where every move by each side makes the other respond more negatively, like those horrible arguments with your spouse where everything you say makes the other person dig in their heels more fiercely.

These days we Americans live not only with political schismogenesis, but also religious schismogenesis. The political scientists Robert D. Putnam and David E. Campbell, in their book “American Grace,” found that “recent years have seen the sharpest points of disagreement between religious believers — of nearly all stripes — and those who denounce religious belief of all types.” The last few election cycles have made it clear that many evangelicals think that those without religion are dangerously wrong on many issues. A crop of equally committed atheists and agnostics have reciprocated, with vigor. Professors Putnam and Campbell find that it is the people at the extremes who are most engaged in the battle, but all of us see the battle lines clearly drawn.

I think that schismogenesis is responsible for the striking increase in the number of people who say that they are not affiliated with any religion. Since the early 1990s that number has more than doubled to 20 percent from less than 10 percent, and is close to a third for people under 30. We know that most of these people still believe in God or a higher power, whatever they mean by that. It’s just that they are no longer willing to describe themselves as associated with a religion. They’ve seen that line in the sand, and they’re not willing to step over it.

Yet believers and nonbelievers are not so different from one another, news that is sometimes a surprise to both. When I arrived at one church I had come to study, I thought that I would stick out like a sore thumb. I did not. Instead, I saw my own doubts, anxieties and yearnings reflected in those around me. People were willing to utter sentences — like “I believe in God” — that I was not, but many of those I met spoke openly and comfortably about times of uncertainty, even doubt. Many of my skeptical friends think of themselves as secular, sometimes profoundly so. Yet these secular friends often hover on the edge of faith. They meditate. They keep journals. They go on retreats. They just don’t know what to do with their spiritual yearnings.