In 1997, the bookshop chain Waterstone's invited its customers to vote for the "Top 100 Books of the [20th] Century". More than 25,000 people took part in the poll, which was topped by J R R Tolkien's Lord of the Rings. At number 41 on the list, squeezed between Watership Down and The Name of the Rose, Umberto Eco's detective thriller set in medieval Europe, was Sophie's World by the Norwegian writer Jostein Gaarder, a history of western philosophy from the pre-Socratics to Jean-Paul Sartre in the guise of a novel.
Sophie's World was an astonishing success: it sold over 30 million copies in 53 languages after its initial publication in Norway in 1991, and was adapted for the cinema and turned into a computer game. Since then, the general reader's interest in popular philosophy has grown enormously and the trend shows no sign of going into decline. Popular, too, are more conventionally discursive introductions to the subject and essayistic variations on it, such as Alain de Botton's bestselling updating of Epicurus, The Consolations of Philosophy (2000).
Neither Gaarder nor de Botton has held a university position, but it is possible for academics to be popular philosophers, too. A number of notable professional philosophers have, over the past decade, written original but accessible books that have impressed a readership beyond the seminar room. However, they have also attracted the suspicion of colleagues who find it hard to understand why one would want to address anybody but one's peers.
Conversely, the response of professionals to the work of amateurs such as de Botton has generally been hostile. Reviewing The Consolations of Philosophy for the New Statesman in March 2000, Edward Skidelsky accused him of promoting a "decadent" conception of philosophy that "can only mislead readers as to the true nature of the discipline". De Botton, he wrote, treated philosophical theories as if they were little more than "ointment we apply to soothe our various ailments". This was philosophy not as an inquiry into the good life, but as self-help. Speaking to the Independent last year, de Botton attributed such critical reactions to "snobbery". He pointed out that, "for the past 150 years, to be a philosopher meant to be employed by a university".
The professionalisation of philosophy and its contraction into an academic specialism remote from the interests and concerns of an educated public began more recently than de Botton suggests. A hundred and fifty years ago, thinkers and intellectuals such as John Stuart Mill and Leslie Stephen wrote on philosophical topics not for learned journals, but for general periodicals such as the Fortnightly Review and the Edinburgh Review. They were not academics writing for fellow professionals, but "public moralists", to use the historian Stefan Collini's phrase, addressing their fellow citizens.
Uncertainties of chronology aside, de Botton's general point stands: professional anxieties about the perils of popularisation are not new, nor is the hunger of the average reader for philosophical sustenance. Indeed, the two things are closely linked, because popular philosophy has often filled a vacuum left in the culture by professionalisation and academic specialisation.
In the late 1950s, Iris Murdoch, then still a philosophy don at Oxford, bemoaned the intellectual quality of public discourse in Britain. As philosophy becomes "increasingly a matter for highly trained experts", she wrote, "it separates itself from, and discourages, the vaguer and more generally comprehensible theorising which it used to nourish and be nourished by".
What replaced academic philosophy was often just as unedifying, however. In 1957, a year before Murdoch presented her diagnosis, the best-known philosopher in Britain was not the octogenarian Bertrand Russell, who by this time was more celebrated for his (sometimes crankily utopian) political activity than for his philosophical work. Nor was it A J Ayer, professor of philosophy at University College London, a regular contributor to the newspapers and one of the stars of the BBC radio programme The Brains Trust.
The author of the bestselling philosophical book of the 1950s was a young man named Colin Wilson, whose debut, The Outsider, a somewhat confused confection of warmed-over existentialism and hand-me-down mysticism, sold 5,000 copies on the day of its publication in May 1956 - thanks to the sponsorship of Edith Sitwell and Cyril Connolly and a rather breathless profile in the London Evening News, which told how Wilson had come to the capital from Leicester and had saved money by sleeping rough on Hampstead Heath.
Wilson's notoriety was short-lived. By the time his second book, Religion and the Rebel, was published in 1957, his sponsors had abandoned him. He was ridiculed as "a philosophical Tommy Steele", and an article in the London Magazine observed that his "activities [had] become steadily more embarrassing". These included a confrontation with his girlfriend's father, who turned up on his doorstep brandishing a horsewhip.
That such an obviously bad book as The Outsider should have caused such a stir can be explained by the state of academic philosophy at the time, which was dominated by so-called ordinary language philosophers, such as J L Austin and Gilbert Ryle. Theirs was a largely esoteric and self-celebrating activity that bore little resemblance to the subject as it had historically been pursued.
They saw philosophy not as inquiry into the nature of reality, but rather as the examination of how we think about things. And given that the only access we have to how we think is through what we say, philosophy became a form of linguistic analysis. For Austin, it was the "business of becoming self-conscious about the way we use words".
This way of doing philosophy was satirised in a Beyond the Fringe sketch first performed in 1961 by Alan Bennett and Jonathan Miller. They played two philosophers named Bleaney and Urchfont, who, after a moment's uncertainty as to whether the former is using the word yes in its "affirmative sense", conclude that the questions about life and death asked by great philosophers of the past are "entirely irrelevant" to the proper business of philosophy.
The sketch succeeds because it captures what English philosophers sounded like in the late 1950s. It was entitled "Words . . . and Things", an llusion to a book of the same name by Ernest Gellner that attacked ordinary language philosophy. When it emerged that Ryle had refused to allow the book to be reviewed in Mind, the journal he edited, Russell, who loathed Ryle, wrote a letter to the Times in Gellner's defence. The controversy that followed occupied the correspondence pages of that newspaper for much of the final two months of 1959.
Gellner argued that by treating philosophical problems as linguistic muddles for which intellectual therapy was at hand, the ordinary language philosophers had betrayed their calling and trivialised the subject. The ancient Greeks had said that philosophy begins in wonder, but this new approach "killed curiosity". Gellner saw that this had implications for the philosopher's public role, too. If his job is the purely negative one of dispelling misunderstanding, then he can offer no "guidance". Ordinary language philosophy abhorred the "responsibility and power" that philosophers had accepted in the past.
Happily, the picture in this country today looks much healthier than it did 50 years ago. Areas of the subject in which the ordinary language specialists showed little interest - especially moral and political philosophy and metaphysics - are flourishing, and have been doing so for some time. This is largely, it has to be said, because of the influence of American philosophers such as John Rawls and David Lewis.
What's more, a growing number of professional philosophers are realising that rigour and accessibility need not be mutually exclusive - one thinks of the work of Mark Rowlands on the philosophy of mind and animal rights, or any number of books by Simon Blackburn, professor of philosophy at Cambridge.
And, in 2009, the University of Warwick appointed Angela Hobbs as the country's first fellow in the "public understanding of philosophy". It is a sign that philosophers are at last taking their obligations to the wider culture seriously.
Jonathan Derbyshire is culture editor of the New Statesman