Where once Bertrand Russell led, the Rupert Murdoch professor of language and communication now follows. Simon Targett talks to the exponent of this year's BBC Reith lectures, Jean Aitchison True or false? The BBC has invited a windsurfing "wimp" expert who gets her kicks by reading tabloid titillation and running after a Papua New Guinean pidgin called Tok Pisin to deliver the Reith lectures. False? Wrong. True.

Next week, Jean Aitchison, Rupert Murdoch professor of language and communication at Oxford - once dubbed "the Gotcha! chair of page three studies" - will follow in the footsteps of Bertrand Russell and a fanfare of Who's Who figures by walking on to the Reithian rostrum. The Pall Mall world of Reith and the Playboy world of The Sun will rarely have come quite so close.

But Aitchison is no potty professor. She may like weird tongues, she may like the vocabulary in naughty vicar stories, she may even love "Up Yours, Delors" headlines, but she is steeped in the literature of É«ºÐÖ±²¥r, Plato and Sophocles. And if she wears roll necks, sips herbal tea, prefers 1960s decor, and windsurfs on the Thames at weekends, there is nevertheless something of the plain Girtonian bluestocking about her.

Born in 1938, she went to school in Wimbledon, and studied Latin because she found it "fairly easy" and ancient Greek because "it was so bloodthirsty". Throughout her teens, she harboured hopes of cracking the Mycenean language known as "Linear B", which had been discovered by the German archaeologist Heinrich Schliemann in the late 19th century. But when Michael Ventris got there first, Aitchison settled for a place at Cambridge, where she bagged a front seat at the lectures of John Chadwick, the professor who was involved in the decyphering project.

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Aitchison took a double first in classics and in 1960 won a scholarship to Harvard. There, she studied linguistics, and nipped across to MIT to listen to an obscure young don by the name of Noam Chomsky. She planned on doing a PhD. But impecunity - "student poverty isn't new", she says - pushed her into accepting an assistant lectureship at London's Bedford College teaching ancient Greek.

In 1965, she moved across London to teach linguistics at the London School of Economics, and she had every intention of seeing out her university days there. "I was in a cosy little hole at the LSE," she recalls. "I was writing the things I wanted to write, I was being asked around the world, and the students were quite bright." She thought she was "quite lucky", and in 1992, after years' service, she was given a readership. But a professorship was not on the cards.

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Her Oxford colleague Anna Morpugo Davies, professor of comparative philology, thinks that London would eventually have been "shamed into giving her a personal chair". Yet that was unlikely. Although London University had pioneered the study of linguistics in the United Kingdom, giving the School of Oriental and African Studies scholar John Rupert Firth the first British chair of general linguistics in 1944, linguistics teaching at the LSE had been slowly marginalised, and today it is virtually nonexistent.

Also, Aitchison was not, and is still not, renowned as a leading edge researcher. She has worked on language acquisition, noting how a word like "wimp" entered everyday conversation even though it was not listed in any dictionary. She has worked on Indian English. She has worked on obscure creoles and pidgins like Tok Pisin. But when asked to identify her "big idea", professors of linguistics struggle to come up with the answer. Steven Pinker, professor of brain and cognitive science at the Massachusetts Institute of Technology, follows a long pause with a diplomatic response: "When I read her books, I don't come away thinking about her own research. But that doesn't mean it's not there." Less diplomatically, Peter Matthews, professor of linguistics at Cambridge, says "she is not one of our leading scholars in terms of originality", adding that "there is no 'big idea' that I would associate with her". Even Jim Hurford, professor of linguistics at Edinburgh University, who is organising a conference with Aitchison in April, stumbles for an appropriate comment: "I'm sure she does have a big idea, but I can't immediately put my finger on it."

Her great redeeming feature is what Davies calls "her gift" for taking linguistics beyond the groves of academe. Matthews notes: "She is an extremely good populariser, and she has the knack of communicating difficult concepts without getting things wrong or sacrificing something important." Pinker agrees: "She doesn't, as we say over here, 'dumb things down'." Certainly, her books have sold well, if as undergraduate textbooks rather than scholarly monographs. Articulate Mammal, first published in 1976, has been reprinted 11 times in three editions and translated into six languages, including Polish, Persian and Belorussian. Her other main books, Language Change and Words in the Mind, have enjoyed similar popular success, and have been translated into languages as different as Portuguese and Korean.

It was partly this penchant for populist linguistics which recommended Aitchison to the selection board for the Murdoch chair. With hindsight, she would seem to have been the obvious choice. Yet she very nearly missed her chance. Even now, John Wells, a Cambridge contemporary who is now professor of phonetics at University College London, says "she was a surprise choice for the Oxford chair".

After Murdoch's announcement of a Pounds 3 million donation to Oxford in May 1990, nearly three years passed before Aitchison was finally esconced in her new chair. "There was a lot of politics and in-fighting," reveals one observer. Aitchison herself responded to the first advertisement, sending for "further particulars". "But when I got the details," she remembers, "I tore them up and threw them away, because it was really a job description which had been written by committee." Anglo Saxon, Shakespeare and The Sun - an expert in all these was what the committee was after. It was a recognition that a fierce battle was raging between the literature lobby and the language lobby within the Oxford English faculty. According to Aitchison, only "a funny bunch of people" applied.

No one was appointed. Some weeks later, Aitchison received a telephone call "out of the blue". Would she like to be interviewed for an Oxford chair? She said yes, found out that the still-vacant Murdoch chair was "actually quite interesting", and took up the professorship in January 1993. Since then, she has caused a stir by introducing a "language, film and media" course during which Oxford undergraduates sit in front of Coronation Street and talk about the northern vernacular. And next month, she publishes her latest work, Seeds of Speech, which addresses the origin of language, a topic she says was until recently "a playground for cranks".

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Like her earlier writings, Seeds of Speech is uncompromisingly popular. There is little fresh research, but the synthesis of ideas from different disciplines is original. It is a textbook technique which, in some cases, leads to the elevation of some novel theories. Take the one about deceiving. Drawn from anthropologists, who have found that chimpanzees are extremely skilled deceivers, the idea is that language was a spin-off from the ability to think about things which are absent or nonexistent.

Seeds of Speech is also popular in the sense that Aitchison treats all language equally. She has little time for Sir Randolph Quirk, making no pejorative distinction between Oxford English and Cor Blimey! English. As she admits: "I would not use the same accent that I use in Oxford if I was in Hackney market. They would say 'who's this toff'."

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Perhaps most obviously, Aitchison writes in a down-to-earth way, piling metaphor on top of metaphor, and liberally quoting anyone from comedian Spike Milligan to crime writer Ruth Rendell. One of her stylistic habits - it is almost a hallmark - is to give a controversy a cliched, or otherwise memorable, tag. The idea that language emerged fairly suddenly she calls "the rabbit out of the hat problem". Others include the "cocktail party syndrome", the "East Side story" and "the nut tree question". Some scholars get irritated by this. Aitchison remembers one reviewer who got unusually hot under the collar about the phrases "Content Cuthbert" and "Process Peggy". But for her, what matters most are the views of the people rather than the professors, and they are universally pro. As she says, striking a defensive note: "I can't tell you how many letters, phone calls and thank yous I've had from students. 'My mind was a blank when I opened the exam paper,' they said, 'and then I suddenly remembered Content Cuthbert and Process Peggy, and those controversies all came flooding back'."

In the Reith lectures, Aitchison will be addressing her biggest audience, and her chosen theme during the five half-hour talks is "The Language Web". She will confront what she thinks are the fundamentals of language: that it is preordained, that it is not primarily for conveying information, that it resembles bird song rather than ape chant. But, in a bid for popularity, she will also confront the "pseudo-worries", as she calls them: whether or not graffiti should be singular or plural, whether or not double negatives are allowable.

But by taking the popular road, she risks belittling the study of language. To a large degree, linguistic theory is founded on elaborate hypothesis rather than hard fact, and there is a sense that Aitchison delights in academic argument for academic argument's sake. She herself acknowledges that she likes "playing devil's advocate", explaining that her books "aren't meant to be believed but subjected to inquiry". This air of intellectual irreverence, this fondness for the latest popular controversy, comes across in her criticism of the antipopular lecturing style of Chomsky, the arch theoretician. "He always used to talk so fast, and in an accent that really wasn't incredibly helpful," she says, "and he was often scribbling things on the board with his back to the audience." Yet for all this, no one has done more than Chomsky to raise the popular profile of linguistics.

After Bertrand Russell delivered the first Reith lecture, Lord Reith recorded that "he went far too quickly and has a bad voice anyhow", yet soon afterwards copies of Authority and the Individual were selling at a rate of 500 a week. What you say is more important than how you say it, and one message from the language fraternity is very serious. Most of the world's 6,000 languages - like some tabloids - are drinking in the Last Chance Saloon.

Jean Aitchison knows this. "It is astonishing," she says, "that everyone makes such a fuss about a few animals and a few plants disappearing, when around 90 per cent of languages could be lost over the next 100 years." She knows too that, however populist, she cannot afford to miss this opportunity to speak up seriously for the future of ethnic languages. It is the first time in nearly 50 years that the Reith lectures have addressed the subject. If another 50 years go by without any international action, then humankind could be standing on the brink of a linguistic apocalypse.

The first Reith lecture will be broadcast on Radio Four on February 6.

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