L'Isle Joyeuse is an extended solo piano piece by Claude Debussy composed in 1904. According to Jim Samson (1977), the "central relationship in the work is that between material based on the whole-tone scale, the lydian mode and the diatonic scale, the lydian mode functioning as an effective mediator between the other two."

Exposition, 1-98

The introduction creates a whole tone context. This changes to an A lydian context which, in bars 15-21, transitions, through the addition of G natural, to the whole tone context of a new motive at bar 21. This A lydian context serves to transition from the whole tone mode on A to the A major context, inflected by occasional lydian D sharps, of the second theme at bar 67.

Middle, 99-159

The other transposition of the whole tone scale, avoided in the outer sections, is used and provides further harmonic contrast.

Recapitulation, 160-end

The second subject appears in pure A major, the "ultimate tonal goal of the piece."

Source

• Samson, Jim (1977). Music in Transition: A Study of Tonal Expansion and Atonality, 1900-1920, p.38. New York: W.W. Norton & Company. ISBN 0393021939.