I was listening to Debussy this morning, and I think Iโve figured out one of the keys to understanding his music. He likes to take a major scale and sharp the fourth. This has several effects:
1. The ascending scale starts with three consecutive whole tones.
2. The interval between the tonic and the fourth step of the scale is a tritone (an augmented fourth, which is the same as a diminished fifth).
3. The I and V chords are unchanged, but the IV becomes a diminished triad. The ii chord, which would normally be minor, becomes major. The vii, which would normally be diminished, is minor.
4. Those tritones give tons of opportunities to modulate smoothly into unrelated key signatures. To a lesser degree, so do the ii and vii chords.
I am coming to appreciate tritones more and more!




