Before leaving the Mozartean museum, let us stop in one final room. It is arranged much like Paillasson's study that we glimpsed in the Encyclopédie, and it is also a museum of sorts: this room finds a man of letters comfortably seated in his office, surrounded by his books, a few decorative pieces adorning his walls, and sculptures posed in various corners. The furniture and objets d’art surrounding the central figure tell a personal history—they are mementos of past travels, gifts from cherished friends, curiosities collected through a lifetime of intellectual pursuits. This is the self-portrait that Diderot paints in his essay Regrets sur ma vieille robe de chambre. Unlike Paillasson's static monochrome engraving, however, the literary image Diderot composes is fully alive and moving. The scene changes before the reader's eyes as one collection of objects is discarded and another displayed in its place, the owner first dashing to hang new pictures and reorder his possessions, then pacing in agitation, and finally clinging to a treasured canvas as though to a long-lost love. Diderot's animated narrative creates a fully dramatized self-portrait, and his lyrical, sometimes elegiac, tone gives his theatrical conceit an almost operatic quality. Indeed, the story he recounts has all the features of a dramma per musica. The main character is not a king or a mythological hero, but he is sovereign of his own philosophical domain, and the action is set within the walls of the private kingdom that is his study. As we witness the evolution of his character, we pass through all the typical stages of a tragic action. We catch sight of the hero's hamartia—hubris—and follow his downward spiral until the moment of anagnorisis. With a dramatic change of heart, the hero recants and this moment of peripeteia paves the way for a scene change and the drama's dénouement. Like all good drammi per musica, a storm scene briefly heightens the action before we reach the reassuring lieto fine.

Diderot's essay bears all the hallmarks of Enlightenment opera, but in fact it was probably written as an introduction to his Salon de 1769, a lengthy review of the exhibition put on by the Académie royale de peinture et de sculpture that year.