All this rambling invasion of theology, ethics, politics, and economics constituted merely a few sides of Diderot’s polymorphous interest and activity; there were many more. Who would have thought that this burly Jack-of-all-ideas would become, overnight, the leading art critic of his age?
In 1759 his friend Grimm, busy with war and Mme. d’Épinay, asked Diderot to substitute for him in reporting to the clientele of his Correspondance the biennial exhibitions of paintings and sculpture in the Louvre. Diderot reported the Salons between 1759 and 1771, and those of 1775 and 1781, sometimes at great length, for in these notes he let himself wander freely over almost every phase of human life. Nothing so fresh and intimate had ever appeared in art criticism before. Some of his critiques were cast in the form of conversations with painters at the exhibition itself; some were introduced as a personal communication to Grimm—as in 1761:
Here, my friend, are the ideas that have passed through my head on seeing the pictures exhibited in this year’s Salon. I throw them upon the paper without much care to select them or to express them.… The only thought I have had in mind is to spare you some moments that you will employ better.70
He went at his new task with ebullient delight. He thanked Grimm for compelling him to look at the exhibited art not with the “superficial and distracted gaze” of the passing crowd, but with the resolve to study each canvas or marble until he really felt its artistry and significance. He had no technical preparation, but he talked with the artists themselves—Chardin, La Tour, Cochin, Falconet … ; he studied their method of composition, brushwork, and coloring. “I opened my soul to the effects [produced by the artist’s labor]; I conceived the magic of the light and the shade; I understood color; I acquired the feeling of the flesh.”71
He became in the end a competent critic of technique. But, disclaiming all technical knowledge, he proposed merely to say what each work meant to him. First he described the subject or story in some detail, since most of Grimm’s clientele would never see the pieces in question; some clients, however, bought pictures on Diderot’s recommendation. Often he would imagine, and graphically recount, the living drama of which the artist represented only the concentrated, telling moment; at times he turned art into literature; and at last he could boast: “Chardin, La Grenée, Greuze, and others … have assured me that I was the only literary man whose images could pass upon the canvas almost as they had succeeded one another in my head.”72
He expressed his preferences and prejudices with unabashed candor. After denouncing almost everything in contemporary French civilization, he defended French painters with patriotic ardor. He called Hogarth a liar and an ignoramus for saying that France had no colorist. “Chardin,” he retorted, “is perhaps one of the greatest colorists in all painting.”73 He was severe on Nattier. He railed at Boucher’s nudes, but enjoyed them. After criticizing the defects in one nude he added: “All the same, let me have her just as she is, and I do not think I shall waste time complaining that her hair is too dark.” A picture of Joseph rejecting the advances of Potiphar’s wife angered him. “I can’t imagine what he could have wanted. I wouldn’t have asked for any better, and I have often settled for less.”74 He sympathized with artists who painted nudes, and especially with sculptors who modeled them; after all, “what can you do in statuary with buttons and pants?”75 He liked Greuze’s pictures of girlish innocence; he fully shared Greuze’s sentimentality; he particularly appreciated the portraits of Greuze’s wife, who had been Diderot’s mistress in his youth. He relished the wild landscapes in Dutch and Flemish art, and found “more poetry in a single tree which has suffered the buffets of the years and seasons, than in all the façade of a palace. A palace must be in ruins to be an object of interest.”76 He rejected the classic emphasis on rationality, order, and harmony, and exalted creative imagination above analytical reason. He called for “compositions terrible or sensuous, which … carry love or terror to the depths of your heart, dissolve your senses, and purge your soul; there is something in that which no rules can achieve.”77 He despised the notion of “art for art’s sake”; art, he thought, had a moral task: “to honor virtue and expose vice.”78
To his observations on the Salon of 1765 Diderot felt confident enough to add an “Essai sur la peinture.” Like Plato and Aristotle he found the essence of beauty in the harmonious relation of parts in a whole; but he suggested that there must also be a harmony of the object with its environment and with its intended purpose. Ideally, he thought beauty might be defined as complete adaptation to function; so a healthy and intelligent man should seem beautiful. Art should select, in a scene, the features that point its significance, and should eliminate irrelevant elements; it need not be a slavish imitation of the objective and indiscriminate reality. Yet the artist must study the natural object rather than ancient models or formal rules; better one Teniers than a dozen fanciful Watteaus. Diderot felt a certain discord between reason and art; he recognized that Boileau’s classical precepts had crippled French poetry. Here he left Voltaire and sided with Rousseau: art must above all be the voice and product of feeling. Therefore he exalted color, while Reynolds in the same decade was extolling design. “Design gives form to beings,” Diderot conceded, “but color gives them life.”79 Goethe found many things in this essay that seemed to him wrong, but he translated portions of it, and described it to Schiller as “a magnificent work; it speaks even more usefully to the poet than to the painter, though for the painter too it is a torch of powerful illumination.”80