Neapolitan chord
(The Neapolitan is also only a half-step away from the diminished supertonic triad in minor in first inversion, E-G-C♯, and thus lies chromatically between the two primary subdominant function chords.)
Whether the added note were notated as a minor seventh or augmented sixth largely depends on how the chord resolves.
In the present example of a C major/minor tonic, the D♭ generally moves down by two steps to the leading tone B♮ (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.
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.)
In very rare cases, the chord occurs in second inversion; for example, in Handel's Messiah, in the aria "Rejoice greatly".
[8] From the early 17th century onwards, composers became aware of the expressive power of the Neapolitan chord, especially to convey moments of intense feeling.
In his oratorio Jephte, Giacomo Carissimi portrays the grief-stricken tears ("lachrimate") of Jephtha’s daughter and her companions at the prospect of her brutal fate.
In his opera King Arthur, Henry Purcell features the chord (D♭ in the key of C minor) among a range of "daring chromatic harmonies"[10] and "strange sliding semitones"[11] to evoke the sensation of intense cold in Act 3 Scene 2, when the spirit of Winter, the awe-inspiring "Cold Genius" is aroused from its slumbers.
In contrast to Purcell, the opening movement of "Summer" from Vivaldi’s The Four Seasons, "a four-note descent transformed by Neapolitan-sixth harmony"[12] enhances the sensation of weariness and languor under the hot sun (A♭ in the key of G minor).
As the sonnet accompanying the music puts it: Sotto dura Staggion dal Sole accesa Langue l' huom, langue 'l gregge, ed arde il Pino; (Under a hard season, fired up by the sun Languishes man, languishes the flock and burns the pine.)
Paul Everett describes the above passage as "a set of disarmingly 'slow' gestures, metrically dislocated, that must represent the lethargy of the anxious man as much as the oppressive heat of an airless day.
19, the episode conveying Christ's agony in the garden of Gethsemane, the Neapolitan chord (G♭ in the key of F minor) is used on the word "Plagen" (torments) in the chorale harmonization sung by the chorus:According to John Eliot Gardiner, "The answering soft-voiced chorus... imbues [the music] with a mysterious quality, almost as though a muted drama is taking place at a distance from the main action – Christ's ‘Agony in the Garden’ and his acceptance of his role as Saviour.
"[19] Scruton sees the "semitone conflict" that recurs in different keys as the movement progresses as a unifying feature that has "penetrated the whole structure of the piece.
In the fourth scene of Richard Wagner’s opera Das Rheingold, the earth Goddess Erda prophesies the impending doom of the Gods.
