Neapolitan chord

In Classical music theory, a Neapolitan chord (or simply a "Neapolitan") is a major chord built on the lowered (flatted) second (supertonic) scale degree. In Schenkerian analysis, it is known as a Phrygian II, since in minor scales the chord is built on the notes of the corresponding Phrygian mode.

Although it is sometimes indicated by an "N" rather than a "♭II", some analysts prefer the latter because it indicates the relation of this chord to the supertonic. The Neapolitan chord does not fall into the categories of mixture or tonicization. Moreover, even Schenkerians like Carl Schachter do not consider this chord as a sign for a shift to the Phrygian mode. Therefore, like the augmented sixth chords it should be assigned to a separate category of chromatic alteration.

In European Classical music, the Neapolitan most commonly occurs in first inversion so that it is notated either as ♭II⁶ or N⁶ and normally referred to as a Neapolitan sixth chord. In C major or C minor, for example, a Neapolitan sixth chord in first inversion contains an interval of a minor sixth between F and D♭.

The Neapolitan sixth chord is an idiom specific to classical music. Other music traditions often feature ♭II harmonies (ex. D♭ major chord in the keys of C major or C minor), but usually in root position. These are sometimes referred to as "Neapolitan" chords, but these rarely follow the classical voice-leading and chord functions described below. For examples and discussion, see Tritone substitution, or the section "In popular music" below.