What is the best recipe for roast heron? Where can one find clear examples of "txt spk" - "I wrote 2 U B 4" - more than a century before the creation of the mobile phone? And who was the first recorded author to use the words "absent", "adoption" and "adulteress"?

Answers to all these questions can be found in a major exhibition at the British Library, Evolving English: One Language, Many Voices (until 3 April 2011), and the accompanying book of the same name by David Crystal, honorary professor of linguistics at Bangor University.

The event is described by one of its creators, Adrian Edwards, curator of printed historical sources at the British Library, as "a celebration of all the different ways people have spoken English throughout the centuries". Another of the curators, head of learning Roger Walshe, claims that it is "the first exhibition ever to explore the development and spread of English from the Anglo-Saxons to the present day".

Though full of evocative objects and recordings, including speeches, announcements and comic wordplay, it obviously represents just the dip of a toe, or tip of a toe, into the British Library's vast collections. So how did Edwards, Walshe and Jonathan Robinson, curator of English accents and dialects, make their selection?

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"It was an organic process," says Edwards. "I have known the collection for 20 years, so I was aware of some good storylines, (and to develop the exhibition I) looked for suitable material, refined the broad themes - and made sure we didn't only use black ink on paper.

"We chose iconic items and famous books from the past, plus a good range of more ephemeral items, such as letters from schoolchildren illustrating everyday language in the 1970s. We spent an enormous amount of time just trawling the collection.

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"Material held in libraries is largely retrospective, which can make it hard to tell much about what is happening now. But we will also be drawing extensively on our sound archive and encouraging visitors to contribute to it. Like our collection of early printed books, it is already the largest in the world."

Two of the key "storylines" are the development of English up to the point when Henry V became the first king to make routine use of it in his correspondence and, much later, the spread of English across the globe. There are samples of Austral English, South African English, Wild West English and many others, not to mention parodies of the particularly ornate style of Babu English used by Indian "native clerks" in the late 19th century. Perhaps most poignant is the Nigerian cut-and-paste guide on How to Write Love Letters and Romance with Your Girl Friends (1965), where suitors are advised to start with "My little Angel" or "Dear beautiful" and sign off with "Nighty - Nighty" or "Cherio darling".

Other sections look at "Accents and Dialects", "English at Work" and "English at Play". Intriguing social history and changing attitudes leap out from every object. The Paragon of Alphabets (1815) includes the Greek historian Xenophon alongside Sorrowful Simon, Timid Tabitha and Wandering Willy among the characters designed to teach children their letters. An advertisement for "Newton's restorative tooth powder", from about 15 years later, is written in a spectacularly high-flown style with references to the patronage of "various illustrious branches of the royal family, nobility, gentry".

The exhibition also explores how far we can capture the "everyday English" of the past, whether from a 15th-century phrase book giving examples of haggling in a market, a collection of slang designed to warn people against the tricks of rogues and beggars, satirical examples of "polite conversation" or a stretch of glum dialogue from one of Harold Pinter's last plays.

English is constantly changing, so many of the most contentious issues relate to attempts to pin it down and regulate it.

There is something surreal and often comic when the full weight of scholarly attention is applied to the more ephemeral or vulgar aspects of a language. One dictionary of slang has a memorable entry under the word "Widdle": "See Piddle".

The pioneering lexicographer Eric Partridge was undoubtedly brave to include the F-word and its cognates in his Dictionary of Slang and Unconventional English (1937). Some definitions of the relevant terms fall back on coy Latin euphemism. Others tend towards the bizarre: "an impotent or almost impotent man whom none but a beggar-woman will allow to 'kiss' her", "inclined, even physically ready, for amorous congress" or "a (notable) performer of, an addict to, the sexual act".

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This leads naturally into the question of whether language ought to be policed. Should we try to stamp out misplaced prepositions, misuses of the word "disinterested", split infinitives and four-letter words? The British Library has assembled examples of tirades against laxity, including A Plea for the Queen's English, which makes it clear that many of today's bugbears - apostrophes in the wrong place, confusions between "lay" and "lie" - were already causing concern in 1860.

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When it comes to spelling, notes Edwards, "Caxton uses 'said' and 'sayd' on the very same page. It became a big debate in the early 20th century, although the Simplified Spelling Society managed to be inconsistent even within its own publications. One of the disadvantages of tidying up spelling is that it means coming down on a particular pronunciation, whereas a more 'organic' spelling allows for variants."

Crystal adds that "the main lesson is evolving diversity. Taking that seriously is a message that some people need to take on board. The exhibition is designed to counter the notion of a single correct or right form of English - it goes beyond ownership or particular countries.

"Though much less than 1 per cent of grammatical constructions and vocabulary is contentious, there are always going to be areas of dispute because languages are continually changing - and that has to be managed to assure communication between generations. There are dozens of different variants of English around the world, but we still need to manage the particular variant that exists in a particular place. Some people need to be taught how to use the linguistic wardrobe available to them, just as children need guidance on what clothes to wear in different situations.

"Academies are doomed to failure when they try to lay down the law and usually have no effect on the natural development of language - Dr Johnson said it was like trying 'to lash the wind'. But they can be important in creating dictionaries and encyclopedias. And, although it is very unusual, one can find cases where someone managed to reform a language."

Noah Webster's Compendious Dictionary of the English Language, published in 1806, for example, not only introduced words such as "caucus", "checkers" and "chowder" but deliberately promoted a distinctively American system of spelling - an essentially political intervention that met with surprising success.

In general, the exhibition comes down on the side of celebrating the variety and mutability of the English language, which is going to keep changing no matter what we do.

"The controversies of 100 years ago", says Crystal, "are not important now, but they needed to be managed at the time - by avoiding a particular word or clarifying the context. There is nothing to be done about the fact that the word 'gay' can no longer be used in some of its former senses. Any change in the language leads to the risk of ambiguity, but that is no reason for prescriptions or banning. There are more important things to write to the newspapers about."

And, for the record, the best way to cook roast heron, according to A Boke of Kokery from around 1440, is to follow the recipe for roast crane; an early example of "text speak" appears in C.C. Bombaugh's Gleanings from the Harvest-fields of Literature in 1860; and the words "absent", "adoption" and "adulteress" all first appear in print in John Wycliffe's Bible from the 1380s. Some elements of the language, then, do not change so quickly after all.

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