Non-traditional scales

When we say non-traditional scales we refer to scales other than the major and minor scales used in baroque, classical and romantic music. Debussy used many non-traditional scales. Some of them are:

1. Pentatonic scales
2. Modes
3. Whole tone scales
4. Original scales

In this prelude, the main theme is based in the pentatonic scales formed by the black keys of the piano:

All notes of the theme, except the F in the third measure, are part of the scale:

There are other pentatonic scales in the prelude. In measures 12-14 the scale is formed by the notes of Gb with a 9^th (Ab), 11^th (Cb) and 13^th (Eb):

In measures 19 - 21. Similarly formed by an Eb Major chord with a 9^th (F) and a 13^th (C):