Seventh Chords

A seventh chord adds a fourth note — a third above the fifth — to a triad. The interval from root to this top note is a seventh, giving the chord its name. Five main seventh-chord qualities appear in tonal music. The major seventh chord (M7) has a major triad with a major seventh (e.g., C–E–G–B). The dominant seventh chord (Mm7) has a major triad with a minor seventh (e.g., G–B–D–F); it is the most harmonically active seventh chord in tonal music.

The minor seventh chord (mm7) has a minor triad with a minor seventh (e.g., D–F–A–C). The half-diminished seventh chord (also called minor seventh flat five, ø7) has a diminished triad with a minor seventh (e.g., B–D–F–A). The fully diminished seventh chord (°7) has a diminished triad with a diminished seventh — an interval of nine half steps, enharmonically equivalent to a major sixth (e.g., B–D–F–A♭). The major-minor (Mm7) built on the dominant scale degree is labeled V7 and is the most common seventh chord in tonal harmony.

Seventh chords add richness and dissonance to harmony. The seventh itself — the interval from root to seventh — is a dissonance that typically resolves downward by step. In functional harmony, V7 resolves to I by contrary motion: the leading tone (7̂) steps up to the tonic and the chordal seventh (4̂) steps down to the third of the tonic chord. This double resolution drives strong cadential motion.