This is part of a series of posts based on articles on music and art in the 11th edition of the Encyclopædia Brittanica, published in 1911. Versions of it are available online at LoveToKnow 1911, although the text has been modified in some cases, and at Online Encyclopedia, although that version invites corrections and updating from readers. The 11th edition is no longer protected by copyright. The passages quoted here are from my printed copy.
Claude Debussy premiered Prélude à 'L'après-midi d'un faune' in 1894, Nocturnes in 1899, Pour le piano in 1901, Pelléas et Mélisande in 1902, La Mer in 1905. However, when the 11th edition of Encyclopædia Brittanica went to press, the world still had not heard Images (1912), Jeux (1913), either book of Préludes (1910-1913) or Etudes (1915), Syrinx for flute (1913), or any of the three late sonatas. Here are some excerpts from the article on Debussy (vol. 7, pp. 906-07) by Robin Humphrey Legge:
The climax of Debussy's creative career was reached by the production at the Opéra Comique on the 30th of April 1902 of his masterpiece Pelléas et Mélisande. Herein lay the whole strength of Debussy's system, the perfection of his appeal to the mind and imagination as well as to the emotions and senses. [...] Probably in the whole range of musical history there has not appeared a more difficult theorist to "place." Unquestionably Debussy has introduced a new system of colour into music, which has begun already to exert widespread influence. [...]Debussy died in 1918, but what this article does not appreciate, because it cannot, is how much more dissonant and atonal Debussy's music became in the last decade of his life. Also, there is no mention of the Javanese gamelan and the possible influence of Asian music on Debussy's tonal palette, only the refutation of an "Annamese" influence (the word is an substitute for Vietnamese).
His scale basis is of six whole tones (enharmonic), as (I) middle C, D, E, G-flat, A-flat, B-flat, which are of excellent sound when superimposed in the form of two augmented unrelated triads, used frequently incomplete (i.e. by the omission of one note) by Debussy. [...] It will be noticed that chords of the 9th in sequence and in all forms occur in Debussy's music as well as the augmented triad harmonics, where the melodic line is based on the tonal scale. This, in all likelihood, is the outcome of Debussy's instinctive feeling for the association of his so-called discovery with the ordinary scale. The "secret," it may be added, comes not from Annamese music as has frequently been stated, but probably from Russia, where certainly it was used before Debussy's rise.