Noam Chomsky started asking awkward questions when he was four. To many people's annoyance, he never stopped. He talks to Harriet Swain

Noam Chomsky is not happy with the idea that he is famous. Perhaps "infamous", he concedes. Outside academe, he is mostly involved with political activists, people who do not automatically confer on him any particular honour. He tries to avoid the prestige lecturers' trail. "I don't think fame is exactly the word." But whatever it is that allows him to pack auditoriums around the globe, that makes him a hit with alternative youth groups, hero-worshipped by some academics and politicians, attacked by others, whatever it is that has made him the most cited living scholar, it makes constant demands.

As he snatches a few minutes before our interview to deal with graduate application papers, his secretary at the Massachusetts Institute of Technology, where he has been a professor for 45 years, is reassuring. "He'll be fine," she says. "He's in a good mood."

Actually, Chomsky apologises, with a diffident smile, for looking a little haggard. He was up until 3am writing. His workload is relentless - it takes him three or four hours a day to deal with email. Other mail takes another couple of hours. Then there are requests for interviews, talks to prepare, departmental administration to address. He spends a lot of time on aeroplanes and fills it by writing, or thinking about future lectures. "I live on a kind of survival strategy," he says. "See if I can make it to tomorrow. There are always deadlines pressing."

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Chomsky is prolific - he has published about 75 books and hundreds of articles. But what really marks him out, and demands every waking minute, is the fact that he is prolific in so many different areas. He is expert in subjects from linguistics to philosophy, history to mathematics. He describes his life as one of "multiple personalities". But it is as a scholar of linguistics and as a political activist and scourge of the American authorities that he is best known.

In linguistics, he thought up the concept of a "universal grammar", arguing that all children are born with a fixed set of mental rules grammar rules, which enable them to make up sentences they have never heard before. They "know" these rules as part of their biological endowment. Language is an essential component of the mind.

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Many argue he has "revolutionised" linguistics. It is certainly rare to read about the subject without his name cropping up. Others argue that he has focused on the wrong area. How does exploring ways in which language is innate help those for whom it is a problem? He is also criticised for concentrating too much on abstract theory.

While his work in linguistics has often put him at the heart of intellectual debates, his political work has more than once put him in jail. In the early 1960s he made a decision to jeopardise a comfortable life of research and family by becoming involved in protests against the Vietnam war. Several nights a week he would address small sympathetic gatherings while hostile mobs made threats outside. Since then he has consistently spoken against "United States imperialism", which, he argues, is "to democracy what violence is to totalitarianism".

He keeps up to date with political developments across the world through newspapers and official documents, always stressing the importance of addressing issues when it can make a difference - in other words attacking wrongs close to home.

He has tenaciously criticised US intervention in East Timor, the Middle East, Bosnia and Somalia. He despises the superpower mentality that chooses to intervene only when it is self serving to do so. He argues that the US and Britain justify their bombing of Iraq by describing Saddam Hussein as a monster who gassed his own people. But they fail to add three words, "with our support". "They supported Hussein in the full knowledge that he gassed his own people," he says.

Recently Chomsky has concentrated on attacking "neoliberalism", by which democratic principles are exploited the better to subordinate people to the profit needs of a handful of private interests.

Among many examples, he includes Washington's "crusade for democracy" in Latin America during the Reagan years when the US sought "top-down" forms of democracy that did not upset traditional structures of power in countries such as Nicaragua and El Salvador. The Reagan government did this, says Chomsky, because its own interests were allied with those of the existing tyrannical rulers.

Chomsky insists that the two sides of his life are distinct. That whereas his work in linguistics takes research, his political ideas just demand a bit of thought. Take, for example, scares over how the "baby boom" generation is to be cared for when it retires.

"It takes five minutes thought to see that that problem was dealt with when they were children," he says. "Anyone who will have to be cared for when they are 70 and when they are 90 also had to be cared for when they were aged zero and when they were aged 20. The US did not collapse under that burden. And now it is a much richer country. This isn't quantum physics. Any school student can figure this out. But what we have rammed into our heads over and over is that the situation is at crisis point."

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This he calls "good propaganda". "Good propaganda is to make people focus on something that is going to motivate them to do what you want," he says. "In this case, turn their money over to Wall Street, instead of giving them enough of a framework that they can see this is the wrong response."

A slight man, now 71, he speaks so hesitantly that it can be hard to detect the bite behind his words. But they still hit home.

In fact, Chomsky inspires admiration to the point of awe. Linguist Raphael Salkie says he is "brilliant" in linguistics, unpretentious and accessible. "A friend said he got a sensual pleasure reading his political writings," he says. "I feel the same thing. I feel all the kinds of illusions and stupidity that get me confused are swept away and I get a beautiful clarity and understanding."

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But, like all famous people, he also has his detractors, people like philosopher Daniel Dennett who calls him an "intellectual bully" and accuses him of making linguistics such a nasty field that many academics now want to avoid it. Geoffrey Sampson, reader in computer science at the University of Sussex and a vociferous Chomsky critic, asserts "most of his ideas about language are mistaken" and "his picture of human nature is a very unattractive one".

Chomsky was born in Philadelphia to first generation Jewish immigrants from Eastern Europe. His father was head of a Hebrew college, working on semitic linguistics. His mother endowed him with a "general concern about social issues". There was always much talk about such issues at home and he had a number of relatives who were involved in radical Jewish politics.

Chomsky claims to have started questioning American society at four years old when he saw people coming to the door selling rags to survive.

He was educated from 18 months in a progressive Deweyite school that emphasised creativity and eschewed competitiveness. He remembers it vividly as "a very exciting experience". His brother, now a doctor, went to the same school, and Chomsky's wife, linguist Carol Schatz, and his sister-in-law, a radical lawyer, came from similar backgrounds.

By the time he was 12 he was hanging around anarchist offices and getting involved in youth activities, particularly in Zionism, or what is now called anti-Zionism. At around this stage he wrote an article for the school newspaper on the Spanish civil war afew years earlier, lamenting the rise of fascism.

However, it was only when he reached high school that he discovered he was clever - and that he hated the competitive, regimented aspects of normal school life.

He was uncertain about academic pursuits when he became an undergraduate at the University of Pennsylvania. He commuted from home, teaching Hebrew in his spare time to earn his keep, and remained active in radical anarchist and left-wing politics. He planned to drop out and live in a kibbutz. But he was persuaded to stay at Pennsylvania in linguistics classes and to further a growing interest in politics and philosophy. "It wasn't a first-rate university at the time but it had some good people scattered around," he says.

Having become a graduate fellow at Harvard, he took up a research post at MIT in 1955 and was also awarded a PhD for his thesis on modern Hebrew. Two years later he wrote Syntactic Structures, which made his name as a linguist, and within four years had been appointed to his first chair.

He began work at MIT in a military lab, which at the time was the freest system around. "When MIT was funded maybe 90 per cent by the military it had no constraints on what it should do," he says. "As it has moved from the Pentagon to corporate funding there are more and more constraints."

He can be scathing about intellectuals, accusing them of pandering to the establishment. "If you are not subordinate to power you rarely make it through the system," he says. This does not necessarily mean suppressing anything. "You just internalise the values so that there are certain things it would not do to say or even to think."

He does not necessarily want agreement. "On the contrary, disagreement is much more interesting. But you have to at least accept some rules of discourse. Like rational arguments matter. Facts matter. And for a large part of the intellectual establishment they don't." He says he has been lucky at MIT because it is a science-based university and therefore naturally more subversive. "Core education in the sciences is getting students to recognise that they are not supposed to respect authority. They are supposed to question and challenge and create good ideas. That comes to exactly the opposite of what most education is, which is mostly designed to instil obedience to authority and belief in power interests."

There is nothing that he would advise people to do that he would not do himself. He has only given up activism because he realised that he was not that good at it. "I can do much better helping people get their thoughts in order," he says. His aim is to get people to question, to think. It must take enormous self-confidence to find himself constantly going against the grain. "I think it is a normal human endowment," he says. "Children have it. They are almost trained to doubt themselves."

There is a knock at the door - he ignored the first, five minutes ago. Someone else needs his time.

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