I N T R O D U C T I O N TERRY PRATCHETT A number of things conspired to cause this book to be written. There was the time when I was in a car with several other grown-up, literate people and we passed a sign to the village of Great Dunmow, in Essex. I said aloud, ''Oh, yes. Home of the Dunmow Flitch.'' They had not heard of it, yet for centuries a married man could go to that village on a Whit Monday and claim the prize of a flitch (or side) of bacon if he could swear that he and his wife had not quarrelled, even once, during the past year. And that he had never wished he was a bachelor again. Back in the late fifties and early sixties the Flitch ceremony used to be televised, for heaven''s sake. Not long after this I did a book-signing on the south coast, when I took the opportunity to ask practically every person in the queue to say the magpie rhyme (I was doing research for Carpe Jugulum).

Every single one of them recited, with greater or lesser accuracy, the version of the rhyme that used to herald the beginning of the 1960s and 70s children''s TV programme Magpie - ''One for sorrow, two for joy''. It wasn''t a bad rhyme, but like some cuckoo in the nest it was forcing out all the other versions that had existed around the country (some of which will appear in a later chapter). Then a distinguished-looking lady was in front of me with a book, and I asked her, with some inexpressible hope in my heart, how many versions of the magpie rhyme she knew. After a moment''s thought, she said ''about nineteen''. And that was how I met Jacqueline Simpson, who has been my friend and occasional consultant on matters of folklore, and once got me along to talk to the British Folklore Society, where I probably upset a few people by saying that I think of folklore in much the same way a carpenter thinks about trees. Some of the things in this book may well be familiar, and you will say ''but everybody knows this''. But the Discworld series, which on many occasions borrows from folklore and mythology, twisting and tangling it on the way, must be the most annotated series of modern books in existence. And one thing I have learned is this: not many people know the things which everyone knows.

But there are some things we shouldn''t forget, and mostly they add up to where we came from and how we got here and the stories we told ourselves on the way. But folklore isn''t only about the past. It grows, flowers and seeds every day, because of our innate desire to control our world by means of satisfying narratives. I used to live a short distance away from a standing stone which, at full moon and/or Midsummer''s Eve, would dance around its field at night, incidentally leaving unguarded a pot of gold which, in theory, was available to anyone who dared to seize it and could run faster than a stone. I went to see it by daylight early on, but for some reason I never found the time to make the short nocturnal journey and check on its dancing abilities. I now realize this was out of fear: I feared that, like so many stones I have met, it would fail to dance. There was a small part of me that wanted the world to be a place where, despite planning officers and EU directives and policemen, a stone might dance. And somewhere there, I think, is the instinct for folklore.

There should be a place where a stone dances. For those who feel the same way we have included a short reading list, in theory for those readers who would like to know more, but also because people who love books always want to recommend them to other people at the least excuse. I N T R O D U C T I O N JACQUELINE SIMPSON Ah yes, I remember it well, that book-signing on the south coast! A misty, moisty November evening in 1997, a long queue inching its way towards a very impressive black hat, the eager voice demanding, ''Tell me everything you know about magpies!'' A little ahead of me in the queue, one woman had been explaining to all and sundry as we waited that it was for her nephew, not herself, that she wanted a signed copy of Jingo. She herself never, ever read novels of any kind, let alone fantasy fiction. ''I only want facts. What''s the point of reading about things that aren''t real? As for a world flying through space on a turtle .'' Her voice died out in a splutter of indig nation, and the combined arguments of a dozen Discworld readers couldn''t budge her one inch. I was not surprised to learn what her job was: she was an accountant - which is to say, very nearly an Auditor of Reality.

Give her a small grey robe with a cowl, and she would find a perfect niche on the Disc. The truth of the matter is, the Disc is the Earth, but with an extra dimension of reality. On the Discworld, things that on Earth are creatures of the imagination (but sometimes quite powerful, even so) are alive and, in some cases, kicking. Sometimes we recognize them at once (is there anyone who doesn''t know a dragon when they meet one?). Sometimes we simply feel that something is deeply familiar and completely right, but we have no idea why. Hours, days or weeks later, we may find the key, when the rich soil that accumulates at the back of the mind suddenly yields the fruit of memory. Then we realize that the key to the familiarity lies in folklore. Whatever is folklore on Earth finds its mirror in the reality of the Disc.

Of course it''s perfectly natural that Mrs Gogol''s house moves about on four large duck feet, because Baba Yaga''s hut spins around on chicken legs in the forests of Russia; of course the Nac Mac Feegle are pictsies, not pixies, because of stories the Scots told about Picts; of course there''s an ancient king sleeping in a cavern deep under a mountain in Lancre, because that''s what King Arthur does in England and Scotland, and the Emperor Barbarossa in Germany. We''ve known about such things for ages, even if we called them fairy tales, myths, and folklore; now that we''re on the Disc, they are real, and we feel quite at home. Well, then, what is the ''folklore'' of Earth, and more specifically of British tradition? It''s the sum total of all those things people know without ever having been officially taught about them, all those stories and images which drift around with no apparent source, all those funny little customs people follow simply because everyone has always done them (and, usually, it''s fun). If we were bookish children, we may remember precisely when we first discovered some of them. Terry still has the copy of Brewer''s Dictionary of Phrase and Fable which he bought second-hand when he was twelve years old, and read from end to end (it cost him 10/6 - OK, OK, 50p, about three weeks'' pocket money). I remember the hot summer day I spent sitting against a haystack, aged thirteen, and embarking for the first time on the genuine full-length tales of King Arthur and his knights, as written by Sir Thomas Malory in the 1460s, funny spellings and weird words included. But most people, most of the time, just grow up having always known how and when to touch wood or cross their fingers, and what happens when a princess kisses a frog or a boy pulls a sword from a stone. They take for granted that there will be pancakes on Shrove Tuesday, pumpkins and scary costumes at Halloween, bonfires on Guy Fawkes Night, mince pies at Christmas.

(Non-British readers, please adjust to fit your own traditional foods and calendars.) So who are the ''folk'' who have all this ''lore''? The answer is, ''any of us''. It''s a mistake to think that the only folklore worthy of the name is what you get by finding the oldest crone in the dirtiest cottage in the poorest village in the remotest mountain valley, and cross-examining her on her deathbed. Every group and sub-group in society has its jokes, its beliefs, its tales and traditions. At this very moment, there are children in the playground giggling over the latest naughty joke (it may or may not be one their great-grandparents knew too); young mothers who take for granted that little girls must wear pink; college students teaching each other the equivalent of Nanny Ogg''s ''Hedgehog Song''. And because where there is fun there is also money to be made, there''s a large-scale trade in birthday cards, Easter eggs, Mother''s Day cards, Halloween masks and so forth, which no parent dares ignore. And any town or pub or castle which wants to attract tourists will go looking for colourful local legends and customs to exploit. The days are long gone when scholars insisted that ''real folklore'' must always be something passed on by word of mouth, not in print.

This was never very realistic, at any rate in literate societies, where generations of poets and novelists and dramatists have drawn material from myth and folk tale, twisted and embroidered it, and then handed it on to future readers. And then, maybe, the readers become tellers in their turn, and hand it on again. The Tree of Folklore has no objection whatever to creative carpenters. Stories and beliefs grow and multiply in all the media available, old and new; they are forever feeding on, and then feeding back into, the rich soup of tradition. Take vampires, for instance. How much of ''what everybody knows who knows anything about vampires'' comes from the basic five-hundred-year-old East European folklore, and how much from novels, films, comics, TV? Specialists can work it out, but does it really matter? Here and now, in the twenty-first century, all vampire lore has blended together into a luscious soup. Folklore may look as if it never changes, but if you keep a watchful eye on it, you will notice some things dying out and others springing up. In Britain nowadays, people do not wear mourning f.