Neapolitan chord

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In music theory, a Neapolitan chord (or simply a "Neapolitan") is the first inversion of a major chord built on the lowered second (supertonic) scale degree. It is notated either as ♭IIb or N⁶. The same chord played in root position (with the root note in the bass) is not a Neapolitan chord but a major flattened supertonic chord. This would be notated as ♭II.

The Neapolitan chord is so-called because it is erroneously attributed to Baroque composers in Naples, Italy, who used it at dramatic moments in their operas. Although the Neapolitan chord was used by these composers, it originated earlier. It is known as the Neapolitan 'sixth' chord due to the interval of a sixth between the 3rd and the root note of the chord. For example, in the key of C major the Neapolitan sixth chord would consist of the notes ♭D (the root note), F (the third) and ♭A (the fifth) with the F in the bass to make it a ♭IIb or N⁶ rather than a ♭II. The interval of a sixth is between F and ♭D.

In tonal harmony, the function of a Neapolitan chord is to prepare the dominant, substituting for the IV or ii (particularly ii⁶) chord. For example, it often precedes a perfect cadence, where it functions as a subdominant (IV). In such circumstances, the Neapolitan sixth may be considered to be a type of chromatic alteration of the subdominant. For example, in C major, the IV (subdominant) triad in root position contains the notes - F-A-C. By lowering the A by a semitone to A♭ and raising the C by a semitone to D♭, the Neapolitan sixth chord F-A♭-D♭ is formed. In C minor, the resemblance between the subdominant (F-A♭-C) and the Neapolitan (F-A♭-D♭) is even stronger, since only one note differs by a half-step. (Note that the Neapolitan is also only a half-step away from the diminished supertonic triad in minor in first inversion, F-A♭-D, and thus lies chromatically between the two primary subdominant function chords.)

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 an awkward 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.

If a I6/4 (or i6/4) chord is placed between the Neapolitan sixth and the dominant, 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 top part. If the root or (doubled) third is in the top part, 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 lowest part. (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.)

The flattened major supertonic chord is sometimes used in root position (in which case there may be even more concessions regarding consecutive fifths, similar to those just discussed); an example occurs in the second last bar of Chopin's Prelude in C minor, Op. 28, No. 20. In very rare cases, the chord occurs in second inversion; for example, in Handel's Messiah, in the aria "Rejoice greatly".^[1]

The Neapolitan sixth chord is particularly common in minor keys. As a simple alteration of the subdominant triad (iv) of the minor mode, it provides contrast as a major chord compared to the minor subdominant or the diminished supertonic triad. The most common variation on the Neapolitan chord is the Neapolitan major seventh, which adds a major seventh to the chord (this also happens to be the tonic).

Acommon use of the Neapolitan chord is in tonicizations and modulations to different keys. It is the most common means of modulating down a semitone, which is usually done by using the I chord in a major key as a Neapolitan chord (or a flattened major supertonic chord) in the new key, a semitone below the original.

Occasionally, a minor seventh is added to the Neapolitan chord, which creates a potential secondary dominant that can allow tonicization or modulation to the ♭V/♯IV key area relative to the primary tonic. For example, in C major or C minor, the Neapolitan chord with added seventh D♭7 can lead to G♭ (or F♯) major/minor. Another such use of the Neapolitan is along with the German augmented sixth chord, which can serve as a pivot chord to tonicize the Neapolitan as a tonic. In C major/minor, the German augmented sixth chord an enharmonic A♭7 chord, which could lead as a secondary dominant to D♭, the Neapolitan key area. As the dominant to ♭II, the A♭7 chord can then be respelled as a German augmented sixth, resolving back to the home key of C major/minor.

Chords
By Type	Triads	Major · Minor · Augmented · Diminished
	Sevenths	Major · Minor · Dominant · Diminished · Half-diminished · Minor-Major · Augmented major · Augmented minor
	Extended	Ninth · Eleventh · Thirteenth
	Other	Sixth · Augmented sixth · Suspended · Altered · Added tone · Polychord · Quartal and quintal · Tone cluster
By Function	Diatonic	Tonic · Dominant · Subdominant · Submediant
	Altered	Borrowed · Neopolitan sixth · Secondary dominant · Secondary subdominant

[edit] Notes

1. ^ Christ, W, DeLone, R, Kliewer, V, Rowell, L, and Thomson, W, Materials and structure of music, volume 2, 2nd edition 1973, Prentice Hall, NJ, pp. 146–7.