the characteristic plain-song progressions to secure, for special purposes, a particular and definite effect of color; but no one had ever before deliberately adopted the Gregorian chant as a substitute for the modern major and minor scales, with their deep-rooted and ineradicable harmonic tendencies, their perpetual suggestion of traditional cadences and resolutions.  To forget the principles underlying three centuries of harmonic practice and revert to the methods of the mediaeval church composers, required an extraordinary degree of imaginative intuition; purposely and consistently to employ those methods as a foundation upon which to erect an harmonic structure most richly and elastically contrived—­to vitalize the antique modes with the accumulated product of modern divination and accomplishment—­was little less than an inspiration.  Debussy must undoubtedly have realized that the familiar scales, which have so long and so faithfully served the expressional needs of the modern composer, tend now to give issue to musical forms that are beginning to seem clichee:  forms too rigidly patterned, too redolent of outworn formulas—­in short, too completely crystallized.  Chopin, Liszt, Wagner, and after them the modern Germans and their followers, found in a scale of semitones a limited avenue of escape from the confinement of the modern diatonic modes, and bequeathed to contemporary music an inheritance of ungoverned chromaticism which still clogs its progress and obstructs its independence.  Debussy, through his appreciation of the living value of the old church modes, has been enabled to shape for himself a manner of utterance which derives from none of these influences.  It is anything but chromatic; indeed, one of its most striking characteristics is its use of whole-tone progressions, a natural result, of course, of its dependence upon the old modes.  Other contemporary Frenchmen have made occasional use of Gregorian effects; but Debussy was the first to adopt them deliberately as the basis of a settled manner of utterance, and he has employed them with increasing consistency and devotion.  His example has indubitably served to enrich the expressional material at the disposal of the modern music-maker—­there cannot conceivably, in reason, be two opinions as to that:  he has acted upon a principle which is, beyond question, liberating and stimulating.  And the adaptability to his own peculiar temperament of the wavering and fluid order of discourse which is permitted by the flexibility and variety of the antique modes is sufficiently obvious.

His resort to Gregorian principles is, it has been observed, far from being a matter of recent history with him.  Almost twenty years ago we find him writing in the spirit of the old modes.  Examine the opening phrases of his song, Harmonie du Soir (composed in 1889-1890), and note the felicitous adaptation to modern use of the “authentic” mode known as the Lydian, which corresponds to a C-major