Seventeen volumes of text and eleven of plates, published between 1751 and 1772: some seventy thousand entries gathered from roughly a hundred and fifty contributors, and inside a single alphabet the process for making steel sat a few pages from the article on God. That was the argument, and nobody had to state it. In the France that produced it a book could be condemned by the Parlement of Paris and burned by the public hangman, and its author locked up on a royal warrant that required no trial; knowledge was property, with the guilds owning the secrets of the trades and the theologians licensing what could be said about nature. The counter-attack took the form of a dictionary.
Its editor wrote nearly six thousand of those entries himself, and he already knew what the state did to men who published. The Pensées philosophiques went to the fire in July 1746. In 1749 the Lettre sur les aveugles — where a dying blind mathematician asks for a God he can put his hands on — brought a warrant to his door on 24 July and three months in the tower of Vincennes, with Rousseau walking out from Paris to visit him there. He came home in November and, for the next quarter-century, wrote for the drawer.
The Encyclopédie consumed him anyway. The first two volumes were suppressed in 1752, and in 1759 the Parlement condemned the whole enterprise and the royal privilege was withdrawn; d'Alembert, his co-editor, resigned. Diderot carried the last ten volumes alone, into a false Neuchâtel imprint. Then in November 1764 he discovered that his own publisher, Le Breton, had been quietly cutting the sheets after he had passed them — some three hundred pages of the boldest material gone, unrecoverable, already printed. He wrote Le Breton a letter of pure fury and went on working.
He was fifty-one and could not raise a dowry for his daughter. In 1765 Catherine of Russia bought his library for fifteen thousand livres and paid him to keep it on his own shelves.
The philosophy is in what he did not print. Diderot came to think that sensibility — the capacity to feel — is not something added to matter from outside but a property matter has, latent in stone and released by the ordinary business of eating, growing and generation. There is no soul doing the perceiving, and no design at the beginning: living things assemble themselves, organ by organ, out of stuff that was never inert. He worked this out in Le Rêve de d'Alembert in 1769 and put it in a drawer. It follows that a person is a physical process, not free in the way courts and churches require — and Diderot refused the comfortable exit. He denied that we are blank material to be moulded, and kept arguing for a morality a determined animal could actually have.
So the record delivered him late. Le Rêve de d'Alembert reached print in 1830, Le Neveu de Rameau was read in Europe first as a German translation by Goethe in 1805, and the manuscript Diderot actually wrote surfaced only in 1890, in a Paris second-hand shop. Post-revolutionary France, canonising Voltaire and Rousseau, had little use for him. Readers came back to him after 1870 and have not stopped; he is now read as the most searching mind of the lot.