Big posers come by male order

SOPHIE'S WORLD by Jostein Gaarder, trs Paulette Moller Phoenix House £16.99

ABOUT two thirds of the way through this book, the principal characters are struck by the thought that they might not exist - they might be mere figments of their author's imagination. One turns to the other and says: "This book ... is in reality a textbook on philo-sophy."

"A textbook?"

"All our conversations, all our dialogues..."

"Yes?"

" ... are in reality one long monologue."

In Sophie's World, whether you are a bemused, puppeteered character or just a baffled reader, it is difficult to tell whose world you are in or who is pulling the strings. And that is just the point (or rather one of many points) this book sets out to make. Conceived as a novel for teenagers, this is a book about a book about the history of philo-sophy. Jostein Gaarder, its real (if I dare say that) Norwegian author, is an award-winning novelist and a former philosophy teacher. He wrote this book because, to borrow the words of his alter ego, "I had been to a large bookstore in Kristiansand and to the library too. But they had nothing suitable for young people."

Evidently Gaarder has tapped a latent demand for accessible philosophy - among all ages. In Scandinavia, where the book appeared in 1991 under a small imprint, it was bought by as many adults as teenagers. In Germany it has sold 500,000 copies in hardback, and here the British publishers are hoping that this American edition will prove as persuasive. A further 15 translations are planned, spreading the word to Israel, South Korea and China.

The story-lesson begins when Sophie, who is almost 15, finds philosophical questions like "Who are you?" and "Where does the world come from?" dropped in her mailbox. This provokes her curiosity - about the source and meaning of life as well as about theidentity of her correspondent. Larger envelopes follow, bearing chapter after chapter of a philosophy course that holds Sophie spell-bound on a whirlwind tour through the minds of Socrates, Plato and Aristotle, Descartes and Spinoza, Locke, Hume and Berkeley.

The ideas of each thinker are treated seriously, yet explained in disarmingly simple terms. Democritus's theory of atoms is like playing with Lego: indivisible basic units from which anything can be constructed, and to which anything will return when deconstructed. In Plato's theory of ideas the phenomena of the material world that take their forms from true, eternal and immutable patterns are like slightly faulty gingerbread men produced from a perfect mould. Kant's claim that our knowledge of the world comes from both sensory perception and reason makes instant sense when Sophie puts on a pair of red glasses.

This grand tour of philosophy leads Sophie and her tutor Alberto to discover what reality they are stuck in (their master's head), and how to escape it (Freud offers a way out via the subconscious). Philosophy is absolutely central to their predicament, and fun: they meet Adam and Eve, Winnie the Pooh, Alice in Wonderland and Mickey Mouse. The philosopher is like a Martian who questions everything, or a child who has not lost the faculty of wonder. The miracle of the universe is compared to a rabbit being pulled out of an empty hat. We are microscopic beings living in its fur. Most people snuggle down complacently, but philosophers put themselves at the very tips of the fur, to catch the magician's trick.

As a popular dissemination of philosophy, this is heady stuff. And Gaarder means to startle, about everything: Big Bang, primal soup, DNA. There are nice touches and ingenious devices. When we reach Romanticism and romantic irony, Alberto demands new chapters to his own story, recalling the line in Peer Gynt: "One cannot die in the middle of Act Five."

Does it succeed as a novel? Probably not. The "novel" is first a primer, hence the index and dates. Plot, characterisation and description have all been subordinated to the didactic task of getting from Socrates to Sartre in 400 pages. Alberto and Sophie's dialogues don't work as conversation. He lectures, she interjects slangy ripostes. (You wonder what was lost, or added, in translation, and suspect the original had more charm.) Sophie seems unsophisticated in everything but her intelligence. Almost endearingly PC, she is gauchely indignant that great male minds like Aristotle and St Thomas Aquinas could not see women as their equals.

But criticisms of its literary merits miss the point. Other books have set out to unravel great mysteries in layman's terms - Stephen Hawking's A Brief History of Time springs to mind - but this one has an energy and enthusiasm that are infectious. Sophie's World is challenging, informative and packed with easily grasped, and imitable, ways of thinking about difficult ideas: a reference book in an odd jacket.