Seventh (interval)

Two sevenths

The minor seventh is one of the most exciting intervals of Western music. It is the defining interval of the dominant seventh chord: in G7 (G–B–D–F) G→F is a minor seventh. In blues and jazz it has a special status as the typical blue note. The seventh sung in the blues corresponds more closely to the natural seventh partial (ratio 7:4), which lies about 31 cents lower than the equal-tempered B♭. That produces the bluesy sound.

The major seventh lies only a semitone below the octave and “pulls” upwards with great tension. In traditional harmony it counted as a dissonance that needed resolution and appeared mainly as a suspension or passing note. Only from the later 19th century on was it increasingly used as a colour in its own right, in Impressionism and especially in jazz: the maj7 chord (Cmaj7 = C–E–G–B) became the trademark of bossa nova and romantic ballads there. The tension is no longer resolved but enjoyed as a colour.

Seventh and chord

A seventh arises when you stack a further third on a triad. The seventh is then the top note, seven degrees from the root. The seventh chord is named after the seventh. The half-diminished seventh chord has a minor seventh on top, the fully diminished one a diminished seventh, which lies nine semitones above the root.

On the guitar

The minor seventh lies ten frets above the fretted note, the major seventh eleven. On the high E string (329.63 Hz) D sounds at the 10th fret and D♯ at the 11th. The 11th fret lies very close to the 12th fret, the octave. This very closeness creates the strong tension of the major seventh.

Common mistakes

• Mixing up minor and major seventh: Ten against eleven semitones.
• Mixing up seventh and sixth: The seventh spans seven degrees.
• Reading the major seventh as a mistake: In jazz and bossa nova it is a deliberate sound.