A Dictionary of Music and Musicians/Sixth

SIXTH. The interval which embraces six degrees of the scale. There are three forms—the major, the minor, and the augmented. (1.) The major sixth, as CA, contains 9 mean semitones, and the ratio of its limiting sounds in the true scale is 5:3. It is a concord, and in harmony is regarded as the first inversion of the minor common chord. (2.) The minor sixth, as CA♭ or EC, contains 8 semitones, and the ratio of its limiting sounds is 8:5. It is also a concord, and in harmony regarded as the first inversion of the major common chord. (3.) The augmented sixth, which is arrived at by flattening the lower or sharpening the upper extreme sound of a major sixth, as D♭ B, or A♭ F♯, contains 10 semitones, and the ratio of the limiting sounds is 125:72. The augmented sixth is a discord, and is usually resolved by moving each note a semi tone outwards to the octave, the sharpening or flattening of one of the extreme sounds already implying a straining in that direction. [See Harmony.]

[ C. H. H. P. ]