Minor seventh

Softly dissonant

The minor seventh is one of the most exciting intervals of Western music. With the ratio 9:5, or approximately 7:4 in the harmonic series, it sounds softly dissonant, earthy and full of longing for resolution. It is the defining interval of the dominant seventh chord: in G7 (G–B–D–F) G→F is a minor seventh. In the blues, seventh chords are used very often. In pop the minor seventh is everywhere; it is the basis of every “bluesy” colouring.

The blue seventh

The seventh sung or played in the blues corresponds more closely to the natural seventh partial, which lies about 31 cents, just under a third of a semitone, lower than the equal-tempered one. This slightly lower note, the “blue seventh”, produces the bluesy, yearning sound. Many listeners find it “interestingly strange”, because it departs from equal temperament.

In jazz the minor seventh is a central note in practically every II–V–I pattern. On the guitar it lies ten frets above the fretted note: on the high E string (329.63 Hz) D (587.33 Hz) sounds at the 10th fret.

Common mistakes

• Confusing it with the major seventh: Ten against eleven semitones.
• Hearing the seventh as a “wrong note”: It is the built-in tension note of the dominant seventh chord.
• Reading the blue seventh as an intonation error: It deliberately lies lower than the equal-tempered grid.