The strange thing about philosophy is that it is more interested in cultivating a scrupulous inner ethic of thought than in accumulating a wealth of outward knowledge. Philosophy, you might say, is not so much a research programme, more a way of life. Biography, autobiography, and hagiography have therefore always had an important place on the philosopher's bookshelf. And the same, one might think, should apply to the novel, the art that specialises in inwardness. In the event, though, the relationship between philosophy and the novel is one of the great missed appointments of cultural history. There are exceptions perhaps: Sartre portraying elemental philosophical experiences, George Eliot applying the conclusions of philosophical ethics, or Kierkegaard enticing his readers into philosophical crises. But philosophical novels like these do not include much discussion of philosophy as such; and Jostein Gaarder's Sophie's World ("the novel that thinks it's a history of philosophy") is meant to fill this gap. It was published in Norwegian in 1991, as a lightweight primer for schoolchildren. But it is now an international best-seller - half a million hardbacks, for example, in Germany alone. "Europe's hottest novel," according to Newsweek, "is about philosophy."

Sophie's World retells a familiar old tale about how civilisation was born with the invention of philosophy in ancient Greece, went into decline in the Dark Ages, was revived by Bacon and Descartes, and has been getting more and more philosophically refined ever since. This is a novel which has swallowed a Victorian history of philosophy, in short, and (unlike most novels, unfortunately) it even runs to a comprehensive index, from Abraham and the Absurd to Zeno and Zeus.

But Sophie's World is a novel, not a textbook. It tells the tale of a pretty air-head called Sophie, who is befriended, just before her 15th birthday, by a mysterious middle-aged man with a beret and a beard. Her mother, understandably, does not approve; and Nabokovian readers will also start to sniff something exotic. But there is nothing to get excited about: the stranger is a philosopher, not a philanderer. All he wants to do is strip Sophie of her prejudices, and take her off on a journey through intellectual history, starting with Thales and gliding through every "great epoch in the history of mankind" before finally settling down with Sartre.

Nearly every chapter of Sophie's World is dominated by transcripts of the philosopher's lessons. They are lucid, after the style of Open University units, and Sophie laps them up with squeals of pleasure. ("Empedocles must have been pretty smart," she muses at one point; and on being told about neo-Platonism, she "experienced something unforgettable".) Half way through, however, the plot twists. There is still not a flicker of passion between them, but Sophie and her teacher suddenly realise that they are only fictional characters in a guileless novel (which some readers will have worked out already). This inner novel is being written by a man who imagines that if everyone in the world studied philosophy (or the history of philosophy - he does not see any difference) then peace would reign perpetually; and he is writing a book called Sophie's World for his daughter's 15th birthday. (The little darling finds the gift "terribly exciting", of course.) This narrative backtracking could have been the occasion for a glorious unravelling. The story of western philosophy was devised at the time of the rise of the novel, after all, and a novel which sent it up would indeed be something to savour - a book to set alongside Robert Pirsig's classic, Zen and the Art of Motorcycle Maintenance, where the authentic philosopher, interested only in what he cannot understand, has long ago been carted away by the police.

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But Gaarder is in the tradition of Enid Blyton rather than Pirsig. He does not try to be cleverer than his dozy characters, and Sophie's World is as clean of irony as of lasciviousness. The whimsical twist in the plot does not touch the solidified platitudes that make up the philosopher's gratuitous course. His unthinking identification of philosophy with civilisation and his smooth cocoon of Euromystical complacency emerge without a scratch. At the point where he and Sophie realise that they are only fictions, he has not yet reached Kant, and quite apart from having to meet a few trolls and matchgirls along the way, he will need another 200 pages to bring his monologues to their predestined existentialist conclusion. We may or may not thrill to their fairytale attempts to break out of the book that contains them; but surely the neglected plight of the thinkers trapped inside the philosopher's dank lectures is more worrying by far.

Jonathan Ree teaches philosophy at Middlesex University.

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