What is this religion thing anyway? It seems odd to say that I am venturing into uncharted territory. After all, the realm of faith is a populous one, and there have possibly been more books dedicated to religions of various kinds than to any other subject. Nevertheless, it is hard to say what kind of a thing religion actually is.

We tend to assume that 'a religion' is a set of statements which one either believes to be true or does not. In that sense, a religion is a hypothesis or perhaps a manifesto. It may be associated with a general outlook, certain festivals, and moral laws, with which the members of the religion may or may not conform. But this only determines whether they are good or bad members of their religion; the religion itself is defined by what they believe.

Yet this doesn't seem to fit with the impression I've gathered of religion in other times and places. I once tried to write an essay on the relationship between 'religion' and 'society' in mediaeval England and spent half the word-count unsuccessfully trying to disentangle the one from the other. For a people who truly believed that God created and directed the world, it was difficult for anything to be completely outside the religious sphere. The term 'secular' could mean someone who was a priest rather than a monk.

Moreover, there are plenty of secular Jews, lapsed Catholics, even non-believing Muslims - people who acknowledge that their culture and outlook belong to a certain religion even if their creed does not. Beyond the monotheist tradition of the West and Middle East, the distinction is futher blurred. Buddhism, for example, seems to give belief a back seat - at least in the form in which it is becoming popular in the UK. This western neo-buddhism, with its emphasis on meditation, does not claim to be a set of truths on which to base a way of life, but a way of life which leads to truth.

This repackaging of buddhism has been a particularly successful piece of marketing, allowing people to take part in a spiritually satisfying way of life without having to start with the most difficult (and unfashionable) step of believing anything specific about the world. It has also remarkably preserved buddhism from the intellectual attacks that have been levelled against Christianity and, by extension, the other abrahamic faiths. Dawkins, for example, considers buddhism properly a philosophy more than a religion - and he does not pause much to consider what, if anything, he means by that terminological difference.

But I wonder whether our doctrinal view of religion is based on a similar but spectacularly unsucessful rebranding on the part of Christianity - a result of the very world view it sought to counteract. Perhaps as the 'scientific', literalist outlook advanced, certain church leaders felt threatened by the answers it gave about the world and felt that they had to meet it head on, on its own territory. Instead of treating statements about the world (creation in seven days, for example) as the products of a certain time period, part of a particular society or culture but not essential to faith, they put them at the centre of religion and seemed to concede that religion could stand or fall by the same criteria as a scientific hypothesis. By claiming to be playing the same game as science, they opened themselves up to charges of breaking the rules and of special pleading. They turned away from the unique selling points of faith and peddled a cheap imitation of science.

The ultimate result has been faith as add-on. In spite of the fact that mainstream christianity in this country has moved on significantly from this reactionary position, 'organised' religion has remained an optional extra which few people see the need for. It appears from the outside as if it is just a list of beliefs to which a person signs up, with an optional commitment of one hour a week to collective worship plus a list of moral rules (of varying length). It does not seem to offer a new way of life, a new way of seeing the world, an alternative culture and philosophy of living.

Perhaps it can't. After all, this is a post-christian country, and so much of the morality, philosophy and festivity comes as standard. But it is rather alarming that those who do allow their lives to be permeated and directed by faith, or even simply admit that they interpret their lives through a religious outlook, are seen as dangerously fanatical. Religion is tolerated so long as it is neatly compartmentalised. Secularist thinkers, for example, may say that it is perfectly acceptable for the children of fundamentalist christians to be taught creationism in religious studies lessons and evolution in science lessons, as if the two theories did not overlap or contradict in any way - as if somehow the poor children are supposed to believe one thing with their 'religious' brains and the opposite with their 'scientific' brains. Or that it is perfectly okay to oppose vivisection on the grounds that animals 'have rights' but not to oppose abortion on the grounds that foetuses 'have souls'.

But if one travels in the opposite direction, taking the path of modern paganism and western buddhism, one can reach the other extreme - dissolving religion into culture until it becomes indiscernable.

There is a tendency amongst some open-minded and peace-loving souls to dismiss doctrine altogether and proclaim that all religions and moral philosophies are roughly the same. It is remarkable how often one hears that Muslims accept Jesus as a prophet, and how rarely that the Qu'ran denies that Jesus died on the cross and damns as the most heinous of heresies that of 'ascribing offspring and partners to God'. However laudable the intention, this downplaying of doctrinal difference does not do justice to the true variety, complexity and richness of the religious traditions, and is disrespectful to the millions of people who have died for the sake of such differences. It is a sobering and educational thought that we are prepared to kill one another over differences of opinion. That we die for the sake of silly misunderstandings is just bitter absurdity.

Moreover, if religions are just different cultural expressions of the same basic truths, then there is even less reason for anybody in a modern, western culture to try one out. There is a risk of assuming that religion belongs to a primative age, inseparable from social conditions and outlooks which are alien to our own. A religion may be an exotic accessory, but it is ultimately neither possible nor of any value to exchange our existing culture for this foreign alternative.

Far from finding the essence of religion, always new but always the same, it seems that we have two unsatisfactory extremes. One option is to rework religion for the 'modern' age by importing the literalist and objective outlook of mid-twentieth-century science. The other is to see religion as a quaint but harmless aspect of culture, an enjoyable hobby to bring back from one's gap year. Yet these are, I think, just the outward faces of religion - the awkward attempts of the churched and unchurched to speak one another's language. Neither gets to the root of why people believe and what it actually means to those who do. So that is my source of the Nile. That's where I'm headed.