Harmonic functions · Music theory
Tonic, subdominant and dominant; the chords that substitute for one another; what changes in minor; how cadences are classified and how to analyze a progression.
Rest, departure, tension
All tonal harmony rests on three functions. The tonic is rest: the place you leave and return to. The subdominant moves away from it, opening the road. The dominant creates a tension that asks to come back. The simplest phrase in Western music is that journey: T – S – D – T.
What makes the dominant push is the tritone between its 3rd and 7th, B and F in G7. Both notes are a half step from notes of the tonic: B rises to C and F falls to E. Only V⁷ and VII, which contain that tritone, push toward I this way.