Neapolitan Chord - Voice Leading

Voice Leading

Because of its close relationship to the subdominant, the Neapolitan sixth resolves to the dominant using similar voice-leading. In the present example of a C major/minor tonic, the D♭ generally moves down by step to the leading tone B-natural (creating the expressive melodic interval of a diminished third, one of the few places this interval is accepted in traditional voice-leading), while the F in the bass moves up by step to the dominant root G. The fifth of the chord (A♭) usually resolves down a semitone to G as well. In four-part harmony, the bass note F is generally doubled, and this doubled F either resolves down to D or remains as the seventh F of the G-major dominant seventh chord. In summary, the conventional resolution is for all upper voices to move down against a rising bass.

Care must be taken to avoid consecutive fifths when moving from the Neapolitan to the cadential 6
4. The simplest solution is to avoid placing the fifth of the chord in the soprano voice. If the root or (doubled) third is in the soprano voice, all upper parts simply resolve down by step while the bass rises. According to some theorists, however, such an unusual consecutive fifth (with both parts descending a semitone) is allowable in chromatic harmony, so long as it does not involve the bass voice. (The same allowance is often made more explicitly for the German augmented sixth, except in that case it may involve the bass – or must, if the chord is in its usual root position.)