diatonic
Using only the notes of the prevailing major or minor scale.
In Depth
Diatonic means using only the seven notes of the prevailing major or minor scale, with no accidentals or chromatic alterations. A diatonic melody stays within the key, and diatonic harmony uses only chords built from those seven notes.
Most folk music, hymns, and pop songs are predominantly diatonic. The contrast between diatonic and chromatic writing is one of the fundamental tensions in Western music — diatonic passages feel grounded and stable, while chromatic passages add colour, tension, and expressiveness. Understanding diatonic harmony is the starting point for all tonal music theory.
The white keys on a piano form the C major diatonic scale — the only major scale that uses no sharps or flats, which is why C major is the first key most students learn.