Les Caprices de Marianne
Les Caprices de Marianne (Прихоти Марианны)  was an 1833 play by the French dramatist Alfred de Musset (1810–1857), which Tchaikovsky considered as the subject of an opera in 1878 and 1888 (TH 216 ; ČW 456).
On 16/28 August 1878, Tchaikovsky wrote to his brother Modest: "On the subject of reading, I've been going mad on Alfred de Musset. Today I cried out with delight, reading Les caprices de Marianne and, naturally, immediately decided to turn it into an opera. What do you think? I find there is one major shortcoming for the opera; that is, that Cœlio and Marianne never meet or appear together. Really? Nevertheless, it is so delightful! I've fallen in love with Cœlio" . Five days later Tchaikovsky still was not sure: "What shall it be?", he asked his brother, "Romeo or Caprices de Marianne? Write to me what you think about the latter" .
At around the same time, Tchaikovsky told Nadezhda von Meck: "I passionately love all of Musset's dramatic works. How many times have I dreamt of creating a libretto out of one of his comedies or dramas! Alas! most of them are too French, and are inconceivable and would lose all their charm if they were to be translated into a foreign language—for example, Le chandelier or Les caprices de Marianne. Those which are less specifically French—such as Carmosine or André del Sarto, for example—are devoid of dramatic action or are too packed with philosophical reflections, as in La coupe et les lèvres. I don't understand why no French composer so far has drawn from this rich mine" .
Modest's response is unknown, but there were no subsequent references to Les caprices de Marianne until 1888, when Tchaikovsky replied to the French writer Léonce Détroyat, who had offered his services as librettist:
I have never been able to understand why no French composer has ever let himself be inspired by Alfred de Musset's Comédies (with the exception possibly of Carmosine)? As far as I am concerned, I cannot think of anything more deliciously poetic and touching than Les Caprices de Marianne or also Le Chandelier. It is said that these masterpieces are not sufficiently effective for the stage. That may well be so! However, could such discerning and skilful connoisseurs as you and Mr Gallet not manage to adapt for the stage and with a view to the requirements of an operatic scenario the essential elements of these magnificent and powerful works by a poet whom I consider to be one of the greatest to have ever lived? I would prefer Les Caprices de Marianne above all, and I have often dreamed of making a Russian opera out of it. However, the Russian language (for all its great beauty and richness) does not, on account of its roughness and its ever so slightly barbaric flavour, lend itself sufficiently well to this genre of poetry, which is too exquisite, too subtle, too deliciously refined for it to be possible that any language other than yours could render all its charm. My Lord, how thrilled I feel when I think of the good fortune of being able to set to music something by Alfred de Musset. I am writing these lines to you with tears in my eyes—a sure pledge of sincere and fertile inspiration. I am very curious to find out what you think of my idea.
However, Détroyat reported that Alfred de Musset's family would not permit his works to be turned into operas, much to Tchaikovsky's disappointment. "It is very sad that Madame Lardin de Musset is opposed to her brother's masterpieces being set to music", he wrote, "because I regard this whim of hers as an insurmountable obstacle to the realization of the dream I had of creating an opera based on one or several of his comedies!" .