Denis Diderot (1713–84) was a supreme man of letters as understood in the eighteenth century: that is to say, a person seriously concerned with every aspect of human activity and critical inquiry. The range of his writings was astonishing. Moreover, he made important and original contributions in almost every field he engaged with: the natural sciences, moral philosophy, art criticism, the nature of theatre and of acting, the art of fiction. Towards the end of his life, he even travelled to St Petersburg to meet Catherine the Great and advise her on the government of Russia. If his work has a unifying theme, it lies in his exploration of the implications – ethical, political and aesthetic – of a materialist world-view. But rather than proposing firm answers, Diderot asks questions; what is most characteristic of him is his philosophical scepticism and its expression in peculiarly dialogic forms. His intellectual interests and his mode of writing make him the most modern of the great figures of the Enlightenment.

The mind of a sceptic

Diderot was best known by his contemporaries as the editor of the famous Encyclopédie, a vast work published between 1751 and 1772 and comprising seventeen folio volumes of text and eleven volumes of plates. The aim of the Encyclopédie was to collate all the knowledge of the day – scientific, philosophical, historical and practical – and to disseminate that knowledge with a view to reducing theological superstition and improving the human lot. It was a monument to Enlightenment values and its project of demystification. Diderot challenged conventional thinking of any kind and encouraged his readers to beware of preconceived ideas. However, he was interested less in the accumulation of knowledge than in its instability and limits. He had a sense of existence as dynamic and constantly changing.