Functional harmony: T, SD, D

Concept

Every chord in a key plays one of three roles: Tonic (T, home — I, vi, iii), Subdominant (SD, departure — IV, ii), or Dominant (D, tension wanting home — V, vii°). Songs work by setting up patterns of T → SD → D → T. Once you hear functions, you stop hearing 'chords' and start hearing motion.