In a survey of Debussy's oeuvre the critic Ernest Newman wrote, "It would be hardly too much to say that Debussy spent a third of his life in the discovery of himself, a third in the free and happy realisation of himself, and the final third in the partial, painful loss of himself". Later commentators have rated some of the late works more highly than Newman and other contemporaries did, but much of the music for which Debussy is best known is from the middle years of his career.

The analyst David Cox wrote in 1974 that Debussy, admiring Wagner's attempts to combine all the creative arts, "created a new, instinctive, dreamlike world of music, lyrical and pantheistic, contemplative and objective – a kind of art, in fact, which seemed to reach out into all aspects of experience". In 1988 the composer and scholar Wilfrid Mellers wrote of Debussy:

Because of, rather than in spite of, his preoccupation with chords in themselves, he deprived music of the sense of harmonic progression, broke down three centuries' dominance of harmonic tonality, and showed how the melodic conceptions of tonality typical of primitive folk-music and of medieval music might be relevant to the twentieth century

Debussy did not give his works opus numbers, apart from his String Quartet, Op. 10 in G minor (also the only work where the composer's title included a key). His works were catalogued and indexed by the musicologist François Lesure in 1977 (revised in 2003) and their Lesure number ("L" followed by a number) is sometimes used as a suffix to their title in concert programmes and recordings.

Early works, 1879–1892

Debussy's musical development was slow, and as a student he was adept enough to produce for his teachers at the Conservatoire works that would conform to their conservative precepts. His friend Georges Jean-Aubry commented that Debussy "admirably imitated Massenet's melodic turns of phrase" in the cantata L'enfant prodigue (1884) which won him the Prix de Rome. A more characteristically Debussian work from his early years is La Damoiselle élue, recasting the traditional form for oratorios and cantatas, using a chamber orchestra and a small body of choral tone and using new or long-neglected scales and harmonies. His early mélodies, inspired by Marie Vasnier, are more virtuosic in character than his later works in the genre, with extensive wordless vocalise; from the Ariettes oubliées (1885–1887) onwards he developed a more restrained style. He wrote his own poems for the Proses lyriques (1892–1893) but, in the view of the musical scholar Robert Orledge, "his literary talents were not on a par with his musical imagination".

The musicologist Jacques-Gabriel Prod'homme wrote that, together with La Demoiselle élue, the Ariettes oubliées and the Cinq poèmes de Charles Baudelaire (1889) show "the new, strange way which the young musician will hereafter follow". Newman concurred: "There is a good deal of Wagner, especially of Tristan, in the idiom. But the work as a whole is distinctive, and the first in which we get a hint of the Debussy we were to know later – the lover of vague outlines, of half-lights, of mysterious consonances and dissonances of colour, the apostle of languor, the exclusivist in thought and in style." During the next few years Debussy developed his personal style, without, at this stage, breaking sharply away from French musical traditions. Much of his music from this period is on a small scale, such as the Two Arabesques, Valse romantique, Suite bergamasque, and the first set of Fêtes galantes. Newman remarked that, like Chopin, the Debussy of this period appears as a liberator from Germanic styles of composition – offering instead "an exquisite, pellucid style" capable of conveying "not only gaiety and whimsicality but emotion of a deeper sort". In a 2004 study, Mark DeVoto comments that Debussy's early works are harmonically no more adventurous than existing music by Fauré; in a 2007 book about the piano works, Margery Halford observes that Two Arabesques (1888–1891) and "Rêverie" (1890) have "the fluidity and warmth of Debussy's later style" but are not harmonically innovative. Halford cites the popular "Clair de Lune" (1890), the third of the four movements of Suite Bergamasque, as a transitional work pointing towards the composer's mature style.

Middle works, 1893–1905

Musicians from Debussy's time onwards have regarded Prélude à l'après-midi d'un faune (1894) as his first orchestral masterpiece. Newman considered it "completely original in idea, absolutely personal in style, and logical and coherent from first to last, without a superfluous bar or even a superfluous note"; Pierre Boulez observed, "Modern music was awakened by Prélude à l'après-midi d'un faune". Most of the major works for which Debussy is best known were written between the mid-1890s and the mid-1900s. They include the  The suite Pour le piano (1894–1901) is, in Halford's view, one of the first examples of the mature Debussy as a composer for the piano: "a major landmark ... and an enlargement of the use of piano sonorities".

In the String Quartet (1893), the gamelan sonorities Debussy had heard four years earlier are recalled in the pizzicatos and cross-rhythms of the scherzo. Debussy's biographer Edward Lockspeisercomments that this movement shows the composer's rejection of "the traditional dictum that string instruments should be predominantly lyrical". The work influenced Ravel, whose own String Quartet, written ten years later, has noticeably Debussian features. The academic and journalist Stephen Walsh calls Pelléas et Mélisande(begun 1893, staged 1902) "a key work for the 20th century". The composer Olivier Messiaen was fascinated by its "extraordinary harmonic qualities and ... transparent instrumental texture". The opera is composed in what Alan Blyth describes as a sustained and heightened recitative style, with "sensuous, intimate" vocal lines. It influenced composers as different as Stravinsky and Puccini.

Orledge describes the Nocturnes as exceptionally varied in texture, "ranging from the Musorgskian start of 'Nuages', through the approaching brass band procession in 'Fêtes', to the wordless female chorus in 'Sirènes'". Orledge considers the last a pre-echo of the marine textures of La mer. Estampes for piano (1903) gives impressions of exotic locations, with further echoes of the gamelan in its pentatonic structures. Debussy believed that since Beethoven, the traditional symphonic form had become formulaic, repetitive and obsolete. The three-part, cyclic symphony by César Franck (1888) was more to his liking, and its influence can be found in La mer (1905); this uses a quasi-symphonic form, its three sections making up a giant sonata-form movement with, as Orledge observes, a cyclic theme, in the manner of Franck. The central "Jeux de vagues" section has the function of a symphonic development section leading into the final "Dialogue du vent et de la mer", "a powerful essay in orchestral colour and sonority" (Orledge) which reworks themes from the first movement. The reviews were sharply divided. Some critics thought the treatment less subtle and less mysterious than his previous works, and even a step backward; others praised its "power and charm", its "extraordinary verve and brilliant fantasy", and its strong colours and definite lines.

Late works, 1906–1917

Of the later orchestral works, Images (1905–1912) is better known than Jeux (1913). The former follows the tripartite form established in the Nocturnes and La mer, but differs in employing traditional British and French folk tunes, and in making the central movement, "Ibéria", far longer than the outer ones, and subdividing it into three parts, all inspired by scenes from Spanish life. Although considering Images "the pinnacle of Debussy's achievement as a composer for orchestra", Trezise notes a contrary view that the accolade belongs to the ballet score Jeux. The latter failed as a ballet because of what Jann Pasler describes as a banal scenario, and the score was neglected for some years. Recent analysts have found it a link between traditional continuity and thematic growth within a score and the desire to create discontinuity in a way mirrored in later 20th century music. In this piece, Debussy abandoned the whole-tone scale he had often favoured previously in favour of the octatonic scale with what the Debussy scholar François Lesure describes as its tonal ambiguities.

Among the late piano works are two books of Préludes (1909–10, 1911–13), short pieces that depict a wide range of subjects. Lesure comments that they range from the frolics of minstrels at Eastbourne in 1905 and the American acrobat "General Lavine" "to dead leaves and the sounds and scents of the evening air". En blanc et noir (In white and black, 1915), a three-movement work for two pianos, is a predominantly sombre piece, reflecting the war and national danger. The Études (1915) for piano have divided opinion. Writing soon after Debussy's death, Newman found them laboured – "a strange last chapter in a great artist's life"; Lesure, writing eighty years later, rates them among Debussy's greatest late works: "Behind a pedagogic exterior, these 12 pieces explore abstract intervals, or – in the last five – the sonorities and timbres peculiar to the piano." In 1914 Debussy started work on a planned set of six sonatas for various instruments. His fatal illness prevented him from completing the set, but those for cello and piano (1915), flute, viola and harp (1915), and violin and piano (1917 – his last completed work) are all concise, three-movement pieces, more diatonic in nature than some of his other late works.

Le Martyre de saint Sébastien (1911), originally a five-act musical play to a text by Gabriele D'Annunzio that took nearly five hours in performance, was not a success, and the music is now more often heard in a concert (or studio) adaptation with narrator, or as an orchestral suite of "Fragments symphoniques". Debussy enlisted the help of André Caplet in orchestrating and arranging the score. Two late stage works, the ballets Khamma (1912) and La boîte à joujoux (1913), were left with the orchestration incomplete, and were completed by Charles Koechlin and Caplet, respectively.

Source: https://en.wikipedia.org/wiki/Claude_Debussy / License: CC BY-SA 4.0.