No more. When the prudent son of the manse was a student, the Kirk had 1.34 million members. The current membership is less than half that. More worrying for the Church of Scotland's future, only 7,500 babies were christened last year, 500 fewer than the year before. Not all of those will go on to become actively involved, but this is the pool from which recruits are drawn. The effect of it drying up can be seen in every congregation in the land: the men and women in the pews are mostly old. In a major 2001 survey, the most popular religion among Scots under 35 was "None".

The Kirk's loss of 60 per cent of attenders since 1960 is dramatic enough, but the full extent of secularization becomes clear if we take a longer time span. In 1851, about half of Scots regularly attended church, most had some formal Christian instruction, and basic Christian ideas were taken for granted. Now, only 10 per cent attend church and the proportion familiar with Christianity is barely larger. In 1900, being Christian was expected; in 2005, it is exceptional.

It is not easy to explain secularization, but we can eliminate some possibilities. Growing indifference to religion cannot be explained by any particular institutional failure. If only a few organisations were decaying, it might be their fault, but when all the Christian churches (and most of the rest) are declining, the cause must lie in some general social process.

For a while in the 1980s, it looked like circling the wagons might keep the injuns at bay: the two extreme wings of Scottish Christianity - the conservative Catholic Church and the conservative Protestant sects - seemed to be holding up. But their support is now collapsing. With hindsight, we can see that their success was an accidental consequence of having larger-than-average families and being marginal to affluent, industrial, liberal society. Catholics were socially marginal; the Free Churches were geographically remote. The upward movement of Scots Catholics and the outward movement of Highlanders and Islanders has made both populations better integrated. When the social barriers came down, so did the distinctive piety.

Revival might be on the way, but there are good reasons to doubt it. Those who point to a few lively and growing congregations as signs of a better future miss the point that there will always be growth spots amid decay as the dwindling number of Christians huddle together. What matters are the overall totals; outposts of growth make no dent in the 17,000 people lost to the Kirk last year.

When the Kirk has been declining relative to total population for at least 150 years, it is hard to expect next year to be different.

Also, many surveys tell us that adult conversion is rare; if people are not socialised into a faith in childhood, they are very unlikely to acquire one later. We know a lot about family dynamics. When parents belong to the same church, their children have a one-in-two chance of acquiring the faith. When parents are not the same faith (even if both are churchly), the odds on successful transmission are halved again. And the Christian population in many parts of Scotland is getting close to being too small to reproduce itself. Young Christians can either not marry (and, hence, not produce the next generation) or marry out (and, hence, not produce the next generation).

Because the churches have lost the power to stigmatise deviants, their decay has opened the door to a raft of foreign religions and spiritual therapies, and it is now possible for us to cobble together our own spiritual club sandwiches. But, precisely because these are individually tailored products, they do not catch on. What suits my tastes will not match yours. And they are not sustained by a reinforcing community. A world of consumer choice does not produce a shared religion.

Anyway, those who see a bright future for new-age spirituality are not doing the arithmetic. A number of my colleagues have tried to assess the scale of the new age and, no matter how broadly we cast the net, we cannot get beyond 1 per cent of the population having any interest in innovative forms of spirituality, and most of that interest is shallow.

People do not accidentally become religious. Being a Christian is not "natural"; it is an acquired characteristic. Like a language, it must be learned and, if it is not used in the home, in everyday conversation and in public life, it dies out. As the population that speaks a minority tongue shrinks, decline does not slow; it becomes faster. There is no natural obstacle to the death of a language. I do not see why the fate of a religion should be different.

-- Steve Bruce is professor of sociology at the University of Aberdeen and author of God is Dead: Secularization in the West.