An omelette of infants

DIDEROT ON ART: Vols I and II trs John Goodman, Yale University Press pounds 30/pounds 12.95

DENIS DIDEROT has always been recognised as one of the major figures of the French Enlightenment, if only because of his contribution to its chief monument, the Encyclopedie. His reputation has risen, particularly since different aspects of his many-sided talent have appealed to successive generations. His art criticism is especially vulnerable to changes in taste. It first appeared in the edition of his works by his friend Jacques- Andro Naigeon in 1798, 14 years after his death, and a fuller edition followed in 1818, by which time the painters he admired were falling out of favour. This first substantial translation into English was published just before the award of the Turner Prize to Damien Hirst - but forget Hirst: Diderot would have had problems with Turner.

His taste was to some extent dictated by his first readers - around 15 of them, the subscribers to Baron Grimm's Correspondance litteraire, a manuscript "newsletter" dispatched to influential figures around Europe, including Frederick II and Catherine the Great: the restricted readership allowed Grimm and other contributors to be free with their opinions, particularly on religion (in the second of these volumes, Diderot quotes Naigeon's remark that the drops of blood in a painting of Christ's flagellation were nothing compared to all that would be "shed in the name of this accursed religion"). Grimm asked Diderot to review the biennial salon of the Royal Academy of Painting and Sculpture, both as a supplement to the official catalogue for the art collectors reading Correspondance litteraire, and as a philosophical reflection on art. He systematically works his way through the exhibition (more than 200 works for each year), varying the length and sometimes the tone of the entries, but generally adopting a conversational style. "I must revise these four pages if they are to be printed," he writes at one point.

A modern reader may enjoy it most when Diderot is expressing his dislikes. "A nice big omelette of infants," he says of an oval painting of skyborne cherubs by Fragonard; "To the Notre-Dame Bridge!" (the equivalent of the Hyde Park railings), about some landscapes and heads by Francisque Millet; "I won't let him or his works near my daughter", with reference to the libertine artist Pierre-Antoine Baudouin.

He has a moral objection to both Baudouin and his father-in-law, the better-known Francois Boucher. Not that Diderot could be called a prude: he was the author, after all, of the witty and licentious novel, Les Bijoux indiscrets. But he judged works of art according to classical criteria of truth, goodness and beauty, and argues that, "when it doesn't entail any artistic sacrifices", it is better to represent virtue than vice. The paintings that meet with his particular approval are the landscapes of Joseph Vernet, the sentimental genre paintings of Jean-Baptiste Greuze and the still lifes of Jean-Baptiste Chardin.

However, he does not pretend that those notions - truth, goodness, beauty - are unproblematic. His most influential work of literary theory, The Paradox of the Actor, argues that actors are best able to represent a dramatic character's emotions when they are most detached from them: the art consists in depiction, not in feeling what one depicts. Painting, he writes, has in common with poetry that both are founded in morality; and the truth of a painting is mediated by chiaroscuro, colour, expression, composition, "scenic invention", "variety of incident", dessin and so on, all of which is the product of study and patiently acquired technique. His reports on the Salons of 1765 and 1767 (Vols I and II respectively) are about the creation of a language for aesthetics, which is the basis of their claim to be the first modern art criticism in French; and Diderot's reported conversation with an Abbe in the 1767 Salon shows what a keen interest he took in wider questions of language and meaning.

For the professional art historian, these contemporary reports have an obvious value. To the more general reader, they offer a glimpse of one of the most alert minds and attractive personalities of his age, all the closer to us because he does not feel the need to polish his style for the printer. You can catch something of the man in the best-known portrait of him, that by Michel Van Loo, where he is looking up from his desk, with a half smile on his lips. The portrait was exhibited at the Salon of 1767, where he reviewed it in characteristic tone. "Pursing his mouth to make himself look captivating," he writes of its subject, with "clothing so luxurious as to ruin the man of letters should the tax collector levy payment against his dressing gown