What happened in the 1960s is that finally their declines became so extended, and so rapid, that for the first time there were fewer at the end of the year than at the start of the year. That's what prompted a book like Kelly's in the 1970s, because for ten years or more the old mainline had noticed that they were losing membership in an absolute and not just a proportional sense.

If the timeline for the decline is shifted, how does that affect our understanding of the reasons that brought about the decline in the first place?

Once you realize that the decline didn't start in the 1960s, you end up having to go back well into the 19th century in search of the reasons, and you find two. The first is modernist theology. The theology that prevailed in the mainline churches changed dramatically. If you take Paul Tillich's view of God, in which God is essentially something imaginary, then why do you bother to hold a church service in the first place? If there's nothing there to pray to, why do it? The liberal clergy lost their faith, but they continued to hold church.

The second factor was, when the clergy in the mainline denominations decided that they could no longer save souls -- because there were no souls to save -- they decided that they should save the world instead. They switched from religion to politics, and that was a politics of Left-wing radicalism.

It's fine, of course, to be a Left-wing radical. But it was far out of step with the people in the pews. The people in the pews still believed in God, and the people in the pews did not believe that they needed a socialist government next week. Consequently, they stopped sitting in those pews and started going to other pews.

Jeffrey Hadden published a book in 1968 called The Gathering Storm in the Churches. He understood what was happening. He said that a big gap has opened up between the pulpit and the pews. It has two dimensions. One is religious, that the people in the pulpit are no longer really men of God. And the other is political, that the people behind the pulpit are very much men of the Left, and most of the people in the pews are not. The upshot of this, he anticipated, was going to be the continuing decline of the so-called mainline denominations.

And what he said was true. The decline has continued. I believe the Episcopalians lost another 3 percent last year. These have become small, not very important denominations.

So what will happen? Will the mainline denominations eventually decide to shut down shop?

My old hometown is a perfect model of what the American religious market is like. When I was a kid, Jamestown, North Dakota was split about 60 percent Protestant and 40 percent Catholic. The Protestants came in about seven varieties of Lutheran, and the biggest church was the Methodist and the second biggest was the Presbyterians. They're big churches and they stood on the corner of two downtown blocks, two churches facing one another. The Assemblies of God met in an apartment above an auto parts store. The Church of the Nazarene met in what had been a little one-room country schoolhouse that had been moved into town and had a steeple attached to it.

If you go to Jamestown today, the Nazarenes could not even fit their choir into what was their church when I was a kid. The Methodist and the Presbyterian churches are still sitting there on their corners and staring across the street at one another -- but they're empty, except for some very elderly people. The Assemblies of God has got a great big church building on the edge of town, they have two full-time ministers, and they're the biggest church of town.