PREPARE for some disappointment if you imagine that this work is a titillating survey of de Sade's precursors. Yes, some of the divine Marquis's like minded friends put in an appearance, but much more than just pornography is covered in Prof Darnton's surveillance of illicit French reading habits in the decades prior to 1789.

What is most striking is the sheer range of books which were considered unsuitable for public consumption. As Darnton remarks more than once, in an era before television, film and radio had been created, the printed word carried far more authority than today and its potential ability to undermine authority was universally acknowledged.

Hence the spectacle of France's public hangman lacerating and burning copies of forbidden books in the courtyard of the Palais de Justice and, rather less amusingly, the committal to slave galleys of anyone caught smuggling proscribed books into the country.

Inevitably, sources for this kind of information are limited, not least because so many of those dealing in this illicit trade understandably preferred not to keep detailed records Darnton depends heavily on the archives of a major publisher and wholesaler based in the French speaking Swiss principality of Neuchatel.

Just to make his task more difficult still, however, it transpires that the generic term for forbidden literature in France should be "philosophical books".

An extraordinarily diverse range of subjects was included under this heading philosophy, of course, both as we understand "bit today and as it was used to define the work of such political and social theorists as Diderot, Rousseau, Voltaire and Helvetius. But equally, the category of philosophical books could be taken to mean anti clerical treatises, political satire, libelous assaults on court life in Versailles and, of course, pornography.

According to Darnton's research, the No 1 bestseller in the illegal trade during the 20 years before the outbreak of revolution was a rather turgid utopian fantasy called L'An 2440 in which the narrator awakens after a sleep lasting almost seven hundred years and finds Paris immeasurably improved.

Unaccustomed to science fiction, readers of the period adored the book while it may strike a contemporary audience as uninspired, in the eyes of the authorities at the time L'An 2440's sedition lay in its implied criticism of ancien regime France.

The same could also be said of L'An 2440's nearest rival, Anecdotes sur Mms la comtesse du Barry which managed to combine lubricious gossip with damning insight into political corruption, both of these conveyed under the guise of a history of Louis XV's last mistress.

In complete contrast, third place on the bestseller chart was occupied by the distinctly unsexy Systeme de la nature, by d'Holbach. What, if anything, does this listing indicate? Above all, that there was widespread flouting of the publishing laws (even if many books were actually produced just across France's borders) and that all sections of the reading public could justifiably be accused of collusion in the matter.

It has long been accepted that members of the French aristocracy were among the most enthusiastic supporters of the philosophes, many of whose ideas were later employed by revolutionaries to justify their behaviour.

For this question, Darnton is tempted to ask do books cause revolutions? However, the question is, as he would remark himself, mal pose. Of course, books cannot be held responsible for revolution, even in the pre industrial world when there were few other means of widespread dissemination of ideas.

Instead, what this book suggests is that authority undermined, whether by the proposal of fresh political theory or by pornography, will sooner or later have consequences. Presumably nobody settling down with an illicit copy of L'An 2440 in the 1770s ever realised just how grave the consequences of such behaviour would eventually be.