Claude Debussy (1862-1918) conceived his two books of Etudes in 1915, meant to extend the tradition established by a lexicon of European and Russian composers, like Bach, Chopin, Cramer, Czerny, Scriabin, and Rachmaninoff. The German piano virtuoso Walter Gieseking (1895-1956) called the 12 Debussy Etudes "the most difficult music I know." The advent of WW I sent Debussy into seclusion in Normandy, where he lived with his wife and daughter to write these pieces in a modern style he had himself invented. He dedicated the Etudes to Chopin.

Book I opens with a five-finger exercise in homage of Czerny, "pour les cinq doigts." It begins conservatively enough, but by measure 2 subversive elements intrude. Pour les Tierces moves in thirds, vertically and horizontally. Pour les Quartes moves in fluid fourths, with melodic lines appearing out of competing voices and ending on the bass, like a march. Pour les Sixtes is slow and sensual, breaking off twice into agitated interludes. No. V, Pour les octaves, is a joyful, bravura romp with octaves in both hands. Pour les huit doigts or eight fingers moves fast in four-note groups played by both hands,without the thumbs.

Book II opens in what Debussy calls "chromatic degrees" or half-steps, in permutation, with a jaunty melody that appears four times in the left hand. No. VIII is devoted to ornaments, a florid study in ten different key signatures and shifting moods and tempos. No. IX exercises repeated notes and the "Devil's interval" of the tritone. Marked scherzando, the piece indulges in the kind of irony Debussy found in Edgar Allen Poe. No X has competing or opposite sonorities, mostly in tones one half-step apart. The dynamic level changes to a climactic ff, with F Major above E# Major above F# Major, a shimmering moment. No. XI gives us "composed arpeggios," a watery, dreamy landscape piece, marked "seductive." At the end, a moment of cabaret or cheap, street theater erupts. XII is entitled "Pour les accords,” a three-part etude with a slow middle section. Clashing harmonies like F Minor against A Major make the sound unpredictable and disturbed.

Children’s Corner (1908) celebrates Debussy’s daughter Claude Emma or "Chouchou," The six-movement is a tribute to childhood and unconventionality. Dr. Gradus ad Parnassum begins like a Clementi etude in white notes but then deviates from drudgery. Jimbo's lullaby is a tribute to Jumbo the Elephant, who died working for P.T. Barnum. The music tiptoes in a single file like plainchant, delicate and melancholy. Serenade of the doll dances and sings, as girls' dolls tend to do. The Snow is Dancing moves in shifting D minor chords. It feels like a snow globe, like the one in Citizen Kane. The little shepherd begins each of its three phrases with a single line to depict the shepherd's flute. Golliwogg's Cakewalk celebrates minstrel shows and early Jazz, the cakewalk of New Orleans. In the middle, chords from Wagner's Tristan und
Isolde interrupt for a moment of remembered passion, but the joyful dance resumes once more.