diatonic harmony
Harmony built exclusively from the notes of the prevailing major or minor scale.
In Depth
Diatonic harmony uses only chords constructed from the seven notes of the current key. In C major, the diatonic triads are C, Dm, Em, F, G, Am, and B°. These seven chords and their extensions form the harmonic vocabulary of most tonal music.
Understanding diatonic harmony is the first step in music theory — before exploring chromaticism, borrowed chords, or modulation, a student must master the relationships between chords within a single key. The most common progressions in pop music (I-V-vi-IV, I-iv-V, ii-V-I) are all diatonic.
The I-V-vi-IV chord progression is so universal in pop music that it has been nicknamed the Axis of Awesome progression — after the comedy group that demonstrated it underlies dozens of hit songs.