Diatonic triads built on each scale degree provide a closed system of chords that generate functional progressions

A key establishes one note (the tonic) as the home. A major scale contains 7 notes with a fixed pattern of whole and half steps (W–W–H–W–W–W–H). Building a triad (root, third, fifth) on each scale degree produces 7 chords (I, ii, iii, IV, V, vi, vii°), each with major, minor, or diminished quality determined by interval counts. These diatonic chords follow functional tendencies: V and vii° resolve to I; ii and IV lead to V; vi leads to ii or IV; iii leads to vi. The I–V–vi–IV progression is one of the most common in popular music. Most commercial and electronic music uses only these 7 chords.

Examples

In C major: I=C major, ii=D minor, iii=E minor, IV=F major, V=G major, vi=A minor, vii°=B diminished. Progression I–V–vi–IV (C–G–Am–F) is used in ‘Someone Like You’, ‘Hide and Seek’, and hundreds of other songs.

Assessment

Build the 7 diatonic triads in A minor (natural minor). Identify which are major, which minor, and which diminished. Compose a 4-bar progression using only these chords that includes a V→i resolution.