The French writer, philosopher and publisher Denis Diderot was born in Langres in Champagne in 1713, the son of a master cutler. He was educated at the local Jesuit college, his parents intending him for the priesthood, but ran off to Paris in 1728, returning home only very infrequently in later life.

Little is known of his early years in the capital except that he studied at the Sorbonne and earned a precarious living from tutoring, writing sermons (he had studied theology), clerking, journalism and translation. His first original work, Pensées P hilosophiques (Philosophical Thoughts), appeared in 1746. Two years later came the anonymous Les Bijoux Indiscrets (The Indiscreet Jewels), an obscene satirical squib based on the notion that female genitalia might talk.

Dangerous ideas
Diderot collaborated with the composer Jean-Philippe Rameau on a book on musical harmony; then came the philosophical essay Lettre sur les Aveugles (A Letter on the Blind), which argued that morality may be dependent on an individual's perception rather than being a universally applicable code. This interesting thought cost him three months in the prison of Château de Vincennes, a chastening experience which made him more careful.

Other of his notable writings include the satirical Le Neveu de Rameau (Rameau's Nephew) and Jacques le Fataliste (Jacques the Fatalist), an exuberant homage to Sterne's Tristram Shandy , both published posthumously.

Diderot's most impressive achievement however was the 17-volume Encyclopédie, a massive work of research and popularisation which he and Jean d'Alembert directed, edited and partially wrote between 1747 and 1765.

Diderot and d'Alembert's encyclopedia was conceived with the aim of combating ignorance and superstition and spreading enlightenment across France and beyond. It included new categories of knowledge previously considered beneath the notice of the learned, with entries on traditional academic subjects like philosophy, history, theology and law now jostled by others on agriculture, horticulture, mechanical and even domestic arts.

Through a comprehensive system of cross-referencing one entry might link to another, encouraging browsing: an article on sugar, for example, could lead to another on plantations and slavery, or to a recipe for jam or a pear tart.

Groundbreaking work
One can scarcely exaggerate the importance of the Encyclopédie in 18th century Europe, or the challenge its publication posed to accepted ideas about who defines and controls knowledge. Both church and state tried to repress it. Without success: the cultural historian Robert Darnton estimates that 25,000 copies of the formidably expensive work were in circulation across the continent before 1789.

Intellectual authority was moving from the ancient institutions into homes and libraries, both private and semi-public, a development that was accompanied by a new enthusiasm for discussion and "improvement" groups. This democratic tendency would only increase in the following
century.

It is an unquestioned assumption of modern middle class life that reading is a good thing – particularly for children. But in the 18th century this was a strongly contested idea. Conservative commentators were appalled, and perhaps a little intimidated, to see books in the hands of domestic servants, while the notion that a shoemaker or a barber might wish to read was considered laughable.

Even more outlandish perhaps would have been a proposal that the children of the poor should be taught to read at public expense, at a time when, it is thought, not much more than 2 per cent of the population was fully literate.

The greatest leap in mass literacy was to come in the 19th century, but Diderot's Encyclopédie , with its 21 million words and 72,000 articles from more than 140 contributors, was a significant milestone on the way to opening up knowledge to everyone.