'Revolution'. See 'Reference book'

Patricia Fara finds chaos, sedition and sabotage in a taxonomic milestone

Enlightened philosophers enjoyed cracking learned jokes, especially ones with a political edge. When Denis Diderot was editing the Encyclopédie , he tried to fool the censors by smuggling in revolutionary messages. He devoted the first part of his article on "King" to a "bird of the approximate size of a female turkey", and his description of "Cannibals" ends with a cross-reference to "Eucharist, Communion". Struggling to finish the first volume after a spell in prison, Diderot told his readers that his entry "Aguaxima" was pointless because Brazilians were already familiar with the plant and Europeans would be none the wiser for reading about it.

Diderot is the central character in Philipp Blom's lively, empathetic account of the Encyclopédie and its publishing history. The deceptive subtitle, The Triumph of Reason in an Unreasonable Age, echoes Diderot's predilection for ambiguity. Although it encapsulates the self-congratulatory pronouncement of Diderot and his fellow philosophers, Blom reveals the haphazard organisation, emotional conflicts and commercial opportunism riddling a venture that took 20 years - instead of the anticipated three and a half - to complete.

Blom exposes the iceberg of chaos lying beneath the French icon of rational taxonomy. Diderot's subversiveness had acquired a tone of desperation by the time he got to the encyclopedia, in which he admitted that "gross gaffes have slipped in... and there are entire articles which contain not even a shadow of common sense". More soberly, Diderot emphasised the flexibility of an alphabetic order, not foreseeing that the Chevalier de Jaucourt - who supplied more than 15,000 articles in six years - would undermine the decision to exclude biographies by inserting them under cleverly chosen place names. But this does seem an odd tactic: how could French people know that they should look up Wolstrope (Woolsthorpe) to find a life of Isaac Newton?

While the editors quarrelled, sulked and included references to entries that never appeared, their witty subterfuges proved only partially successful. After only the seventh volume, their Jesuit opponents procured a ban, which was itself sabotaged by Diderot's unlikely saviour, the Chief Censor, who connived in a covert rescue operation to smuggle out page proofs.

The work was almost finished when Diderot noticed something strange about one of his earlier "S" articles. Furious, he reported that he "wept with rage" (crying was fashionable for men at this time) when he discovered that he was being censored by his own printer, who was safeguarding his own reputation and profits. Attacks on Catholicism had vanished, and under "Lust" no trace remained of Diderot's accusatory "imagine how many damned there must be, if the slightest sin in this category is damning".

Blom charts Diderot's "transition from literary gadfly to family man and responsible editor", but other characters stomp colourfully through the pages, such as the White Tyrant, Friedrich Grimm. Sophie Volland, Diderot's lover, shared her place in his heart with the powdered and perfumed White Tyrant, and (unsurprisingly) Madame Diderot became disillusioned with her unfaithful husband. Jean-Jacques Rousseau features as the paranoid philanderer with a troublesome bladder, while Voltaire is the scheming "old fox" who persuades Jean d'Alembert to desert his co-editor.

By naming most chapters after an Encyclopédie entry, Blom ingeniously interweaves his flamboyant cast with illuminating discussions of the propaganda they slipped into their manifesto of rationality. Blom appears to have perused all 17 volumes (about 72,000 entries) as well as the additional 11 volumes of plates, although his notes indicate the help he has received from secondary sources. But many of these are old, and they are predominantly French: Robert Darnton is there, but not some other leading English-language scholars, such as Dena Goodman, Roy Porter and Richard Yeo.

As a consequence, Blom's vision of the French Enlightenment seems dated and lop-sided. He celebrates Voltaire as "the secular 'patron saint' of the Enlightenment", whereas the general view now is that the Enlightenment started far earlier and was not exclusively - or even primarily - a French phenomenon. Although Blom confidently elucidates his authors' political and religious manoeuvres, he pays little attention to science and scarcely mentions Newton. This is strange in a book ostensibly celebrating the triumph of reason, since Voltaire himself worshipped Newton as the personification of rationality, and when publicising the Encyclopédie , d'Alembert hailed Newton as the genius who had supplanted Descartes - he "appeared at last, and gave philosophy a form which apparently it was to keep".

Writing a single book about 28 encyclopaedia volumes is a daunting challenge. Far from being an arid, technical analysis, Blom's Encyclopédie conveys the entries' flavour while also providing juicy anecdotes about the idiosyncratic champions of reason and their turbulent trajectory through Enlightenment Paris.

Patricia Fara is a fellow of Clare College, Cambridge.