Sixth (interval)

Two sixths

The minor sixth is the inversion of the major third: together they make exactly one octave (4 + 8 = 12 semitones, or 5/4 times 8/5 equals 2/1). With the ratio 8:5 it sounds yearning and melancholy. Composers like to use it to express longing or wistfulness. In film music it is used to underscore emotional climaxes or tender love scenes.

The major sixth, the inversion of the minor third, is one of the warmest and most cheerful intervals. With the ratio 5:3 it sounds bright and inviting and counts as a typical “folk-song interval”. In functional harmony it is central to the sixth degree of a major key: in C major the A of the tonic substitute Am lies a major sixth above the C. In jazz too it plays a part in 6 chords: C6 is C–E–G–A. A familiar tune that begins with a major sixth is “My Bonnie Lies over the Ocean”.

On the guitar

Eight and nine frets are large stretches. They are mostly not fretted within one hand position but through a position shift or by changing string. On two neighbouring strings the minor sixth can be fretted with an offset of three frets (four on the G and B strings). The ratio 5:3 of the major sixth lies between the 3rd and 5th partials: on the guitar you hear it when you play the harmonic above the 7th fret and then the one above the 4th fret.

Common mistakes

• Mixing up sixth and seventh: The sixth has eight or nine semitones, the seventh ten or eleven.
• Swapping minor and major sixth: Eight against nine semitones.
• Overlooking the inversion: Sixth plus third make an octave; the minor sixth is the inversion of the major third.