'The Gospel must be constantly forwarded to a new address because the recipient is repeatedly changing his place of residence.' Helmut Theitticke

Something's happened out there. People have changed their address, and unless Christians work out where they've moved to we will fail to communicate with them.

We are living through a radical change in the way people understand reality and truth. This change is so fundamental that almost everyone under 30, and many under 40, view the world through a new set of glasses.

Here's how John Carroll describes the changes in his book Humanism: The Wreck of Western Culture:

Some years ago, Alan Bloom wrote in his book The Closing of the American Mind: "There is one thing a professor can be absolutely certain of. Almost every student entering the university believes... that the truth is relative. If this belief is put to the test, one can count on the students' reaction: They will be uncomprehending. That anyone should regard the proposition as not self-evident astonishes them... The relativity of truth is a moral postulate... The only enemy of the true believer... the person who is not open to everything."

As Christians we need to understand this change. The modern world is dying and the postmodern world is rising in its place.

The modern world was formed and dominated by a number of key forces.

Scientific rationalism gave us the autonomous rational person observing, analysing, discovering, conquering the natural world. This produced a confidence that we could explain and eventually control everything.

The Industrial Revolution produced unparalleled economic growth in the West and lifted living standards to undreamt of heights. Along with things like modern medicine and the growth of technology, it led us to develop the idea of unstoppable progress.

The philosophy of liberal humanism placed humanity at the centre of all things. We were basically good. If we applied enough will and education and created the right environment, we would not only overcome all our problems, but create a glittering kingdom of prosperity, freedom and happiness.

In the modern world, of course, there was no need for the transcendent. A scientific breakthrough a day would push the chaos away. In any case, scientific knowledge was about facts, and facts are objective and value free. But beliefs are subjective and therefore private. So God was relegated the private world as unnecessary and irrelevant.

The modern world had its media icons. An icon for continual scientific progress was Star Trek - 'boldly going where no one has gone before'. The icons for the glittering kingdom were the Brady Bunch or the Cunningham family in Happy Days - ideal families in a prosperous, progressive world. Yes, there were occasional problems, but nothing that either Mr Spock or a family conference with some timely advice from dad couldn't fix.

But then things started to come unglued. The ordered and explainable world of the Enlightenment no longer seemed so orderly. We began to suspect it may even be chaotic, random, anarchic. It certainly didn't seem to make as much sense as it once did.

Rationalism and materialism explained God away, but at least we felt that we, humanity, had the answers. Suddenly we weren't so sure. The optimism had gone.

The collapse of the grand visions like Burocommunism; the emergence of old tribal hatreds in places like Yugoslavia; rising Third World debt and the failure of many Third World development schemes; the environmental crisis; AIDS; economic uncertainty; rapid change; high unemployment; the failure of the UN to keep the peace; the uncontrolled growth and degradation of the world's megacities - all this creates a sense of failure and hopelessness.

Our media reinforces this sense of anarchy and senselessness. We watch on the TV news horrific scenes from Rwanda or Bosnia, then we're suddenly switched to a 90-second ad for the latest car. The juxtaposition of images leaves us with a feeling of absurdity. For those of us living in this media zoo, where brilliant and controlled technology reports the chaos and consumerism of an uncontrolled world, it produces a new nihilism.

So autonomous reason, it would seem, has brought as many nightmares as bright visions. Modern culture is exhausted. It may not lie down and die tomorrow, but its heart and soul are in a terminal condition.

Several other forces have fed the development of postmodernity.

The world has come to the city. From the '60s to the '90s we've seen an unparalleled avalanche of people moving into the cities of the world. These cities have expanded to the point where they are mind-boggling. Greater Mexico, for example, has 21 million people.

The modern city is a giant multiracial, multicultural, pluralist supermarket of ideas, cultures and beliefs. It's an exciting and fascinating place. But all of this puts enormous pressures on any remnant of uniform culture and any common vision of reality. In fact, the modern city is producing a new tribalism as we fragment into subcultures.

These vast cities are tied together by the electronic media, which have created an explosion of information. We're now in an unregulated marketplace of ideas and belief systems, all available on the electronic shelves. This makes it difficult to accept any of them as absolutely true.

In this soil grows a new ideology. It teaches that truth, meaning and reality are just social constructs, developed by particular social groups through their language and cultural symbols. There is no objective truth.

This is more than simple relativism. Postmodern ideology rejects all 'meta-narratives' - all big stories that claim to explain all other stories.

There is no one story that explains all the individual stories.

At its extreme theoretical edge, the 'deconstructionists' argue that societies are inherently oppressive and their language and texts are developed to keep people in line. Every text must be interrogated for its hidden repressive ideas. Language does not reveal objective truth. It constructs 'truth'.

All of this has massive implications for the way people view any written text. If language is incapable of disclosing any objective meaning, we are left at the mercy of the presuppositions of the latest revolutionist.

Thanks to the media it's now possible to create a global culture - to have everyone wearing baseball caps and eating McDonalds.

But the media have a preoccupation with the surface of things, with the packaging, the 'wrappers', of consumer society. Style replaces substance. Technique replaces content. Effect replaces integrity. And in the end, the wrapper is the reality.

The media also provide a powerful tool for postmodernism to reconstruction reality for ordinary people. In Media Virus, Douglas Rushkoff makes the point that the media machine is now so ubiquitous and rapid in the dissemination of ideas, images and information that an even or an idea can attach itself like a virus to the media's circulatory system and be pumped through society in minutes. It can invade the cell of the cell of the prevailing ideas of that system with its own DNA and begin to change the current ideas.

An example of what Rushkoff is describing was the beating of Rodney King. Someone with an amatuer video camera recorded it, and in a matter of hours it was around the globe.

All this can profoundly change our feelings or perceptions of the world. But the emergence of postmodernism is affecting general culture in other ways as well.

For a start, relativism reigns. As Shirley MacLaine expressed it, "The truth is not an obstacle for someone like me, for we all create our own reality". This attitude is now deeply embedded in the minds of most people.

Second, postmodernism is "blurring the distinctions". This is best illustrated by contemporary film.

Take the question of right and wrong. Compare the old detective story, where the cops of the FBI get the baddies in the end, with Pulp Fiction or The Silence of the Lambs. Good is no longer strong enough to contain evil.

Male and female are blurred, as in films such as Orlando or The Crying Game. Alien and Total Recall also blur the gender boundaries. In Blade Runner the distinction between real people and androids is blurred to the point where you're forced to ask, Who are the real people? The brilliant special effects in films like Robocop and the advent of virtual reality games have begun to blur the nature of reality in people's minds.

The third effect of postmodernism is that dissatisfaction with rationalism and material has led to a new search for the transcendent. The mystical, the mysterious, the magical - it's every where, from New Age books to fairy shops.

Bono of U2 expressed it well: "the material world is not enough. We had a century of being told by the intellectuals and the intelligentsia that we are all two-dimensional creatures; that if something can't be proved it can't exist. That's over now. Transcendence is what everybody in the end is on their knees for - running at speed towards."

Another effect of postmodernism is that eastern mysticism, environmentalism and element of extreme feminism have converged to resacralise nature. The Judeo-Christian distinction between God and nature has dissolved.

Postmodernism also involves a loss of hope and idealism. Have you notices that the most dominant trend in popular fashion and music has been retro? Fifties and '70s music revivals; gothic grunge and '70s hip in clothing. Why all the nostalgia? Why are we remaking the past? Have we lost our belief in progress? Yes.

The sixth effect is that the quest for truth is turned inward to the personal world of subjective experience. The generation under 30 are the children of the most divorced, most mobile parents ever. All the traditional carriers of meaning and value have been destroyed - family, community, work, and religion. The pace of change is so rapid that there seems to be no fixed points.

Where do you go to find meaning and value? The answer of Generation X is 'within' - into the narrative of my story. When all meta-narratives have been rejected, only my own story seems authentic.

What are we to make of this disintegration of modern culture and the emergence of postmodernism? It would be easy to respond apocalyptically, as some postmodern writers themselves do. W.B. Yeates' poem The Second Coming is frequently quoted in postmodern literature:

We, however, have been instructed by our Lord not to guess the future but to get on with extending the kingdom now. In fact, I think we need to see this generation in Western culture as a time of great opportunity. There are four reasons for this.

Firstly, when all the meta-narratives are breaking down, a vacuum of meaning develops. That is fertile ground for the Gospel.

Second, the human longing for the transcendent guarantees that the need for hope and some moral imperative will, in the end, overpower nihilism. People simply cannot live with nihilism forever.

Third, the chaos and absurdity of the world leads to a longing for good news, and we've got good news.

Fourth, extreme deconstructionism may lead some to a search for an authentic and dangerous Gospel stripped of its Western philosophical trappings and institutional clothes.

The postmodern world is not unlike the first century world of the New Testament. Judaism was in crisis; the religions of the Graeco-Roman world were tired and without moral integrity. There was a growing fatalism, cynicism and loss of hope in pagan culture. Remember Pilate: "What is truth?" Sounds distinctly like a postmodernist!

In ground the Gospel was planted and the church grew. To many in those days the Gospel was either intellectually foolish or an offensive stumbling block in its claims about Christ crucified and risen. But to those whom God called, it was the power and wisdom of God (1 Corinthians 1-2).

This tells us the Gospel is effective in any culture, especially in one like ours. We must not lose our nerve.