A Dictionary of Music and Musicians/Neapolitan Sixth

NEAPOLITAN SIXTH is the name by which a chord consisting of a minor sixth and minor third on the subdominant has long been known; as (a) in the key of C minor

Bach, Violin Sonata, No. 4.

Theorists, starting from different radical assumptions, suggest different derivations for this chord. Some, taking the major and minor scales to comprise all the notes which can be used for essential harmonies, except in the cases where important root-notes in those scales bear fundamental harmonies on such principles as they accept, derive the chord from a combination of two roots; so that the dominant is the root of the two lower notes which are respectively its seventh and minor ninth, and the tonic of the upper, which is its minor ninth. Others, accepting the unquestionably frequent use of some chromatic harmonies in relation to an established Tonic, by many great masters, indicate the major concord on the minor or flat supertonic (as the major common chord of D♭ in relation to the Tonic C) as one of them, and hold the 'Neapolitan sixth' to be its first inversion. Others, again, hold this sixth to be found in the minor scale of the subdominant; and others, yet further, that it is merely produced by the artificial lowering of the sixth for artistic purposes, similar to the artificial sharpening of the fifth which is commonly met with; and that its object may either be to bring the supertonic melodically nearer the Tonic in downward progression, or to soften the harshness which results from the augmented fourth in the chord of the sixth and minor third on the subdominant of the usual minor scale. In the theory which explains some chromatic combinations as reflections of the old ecclesiastical modes, this chord would spring from the use of the ecclesiastical Phrygian, which was the same as the Greek Doric mode, or mode of the minor sixth.

[ C. H. H. P. ]