BY the time the average American reaches 21 years old, he or she has watched 650,000 advertisements. By the time a child enters first grade, it has clocked up 5,000 viewing, hours and 19,000 by the end of high school.

Prof Neil Postman loves producing such figures and statistics such. He does so with the fluency and ease of a person well used to being interviewed. He has written 20 books on media, culture, television and society and has become an icon of media studies for some; a prophet of doom, a Cassandra for others.

For such a devastating critic of television he is clearly a natural for the media. He speaks in a soft, smoke cured, New York accent in what can only be described as sound bites. His arguments come complete with visual images for this televisual age. It was he who offered Las Vegas as a paradigm for the US, the capital of entertainment, rather than the stockyards of Chicago, which he says were the key to an earlier age of enterprise.

That image was in his most popular work, Amusing Ourselves To Death. In that book, Postman argued, alarmingly convincingly, that television was transforming culture into one vast arena for show business in which all public affairs, including education and journalism, had been turned into entertainment.

In his more recent work, the Disappearance Of Childhood, he has argued that television has contributed to the end of childhood itself by ending the divisions between adulthood and childhood and by turning adult "secrets" - about sex, violence and relationships into popular entertainment, and by making news the same as advertising.

Sitting in his office at New York University, where he is the chairman of the Department of Communication Arts and Sciences, he says television would not be a problem in any culture if it simply took its place as one medium among many. "The problem with television and its effects on children is that it tends to become the command centre of a culture. It drives other mediums to the periphery of the culture.

His critique of television leaves little space for those who wish to make a difference between good "and bad television. For Postman, it is not what people watch, but that they watch. Sesame Street, the ground breaking American children's programme, which has, heavily influenced RTE's The Morbegs, would do well in primed time as it is fast moving, with interesting characters and good" music. His point is that it has become hard to distinguish what is essentially children's television: and what is not. A look at the ratings, he says, shows he is not the only one with this attitude. Children like to watch the very same programmes adults watch, and they do.

"Television is not a medium for conveying complex ideas or a sense of continuity. Only print can ado that, but print has been pushed to the sidelines. Print, he insists is linear, sequential and historical. Its grammar is the past tense. The grammar of television is the present.

Television offers no continuity and no "because". Television offers a series of "ands" . "I think it is strange that you can show hundreds dead in a typhoon and then report a football match, followed by a report of a rape. No one ever asks if the fact of the typhoon has any relationship to the report on the soccer match. The question seems stupid because the answer is obvious of course not.

"The idea of causality does not exist in TV's grammar, which is why they can follow that typhoon story with an advertisement."

Television has created a chaotic, almost meaningless world view for young people and while this fragmented, disconnected view of the world might have preceded television - it exists on the front page of a newspaper as well - it has been amplified by television.

But the main difference between print and television is between "and" and "because". TV just offers a series of "and this happened and this happened", whereas as you cannot write two paragraphs without implying a "because".

"You have a kind of grammar embedded in programming. You can show a programme about the troubles in Northern Ireland with people being killed. It can be followed by a comedy. You ask how can that be? Are not people depressed and sad having watched the documentary? How can we expect them to turn their attention to a comedy? I think the metaphysics of television allows that because television does not encourage people to see connections."

His view that young people live in a world that is chaotic, with nothing connected to anything else, is difficult to prove just yet, because television is still a young medium, he says.

The printing press created individualism, but it took 150 years for that to show up in the culture. We are still within the first 50 years of television. It will take time for its full effect to be seen.

In the meantime, we are already undermining the process by which we socialise our children. The literate person is one who understands sequence, the importance of consequences. Television opposes that process.

What of the charge that he simply does not like television? No, he says, he does watch it - for sport and old films, "but I never take it seriously and I am always embarrassed when television tries to be complex or deal with serious issues because I am very much aware that the people who put television programmes together know that people watch television, rather than listening to it. You are not going to be able to say very much on television without showing an image.

The average length of a shot on US television is 3.5 seconds: that means every 3.5 seconds the viewer has to process a different image and a different angle. When you are doing that, it is difficult to concentrate on linguistic content."

But hold on. Surely there is serious television, interviews, current affairs? Postman concedes that something like the US president's State of the Union address, or particularly important announcements, are on television and everyone watches. However, for the State of the Union only one camera is used, with one angle: it is one talking head. Most television programme makers know that a talking head turns people off. Programme makers know that what viewers want is high visual, stimulation. Language plays a very subordinate role.

In The Disappearance Of Childhood, he was unwilling to suggest a solution. He is now willing to suggest a tentative one. Children start watching television seriously at 36 months, he says. Very young children, ask for products they see advertised; they have favourite characters. As soon as possible they should be learning about technology and its effects on our culture. We must understand how television alters our psychic habits, our social habits and our political ideas. "I am not talking about educating kids to use a computer - 35 million Americans figured that out without being taught at school - but to understand how television and other technologies affect us. If we do that we stand a chance of gaining a measure of control over them, so that we can actually answer some of the questions.