Neapolitan Sixth

The Neapolitan sixth is a major chord built on the lowered second degree of the key, usually played in first inversion. In A minor the chord is B♭–D–F with D in the bass; in C minor it is D♭–F–A♭ with F in the bass. It is written N6 or ♭II6. Its root lies a half step above the tonic, and that unexpected half step gives the chord its dark, dramatic color.

How it is built

1. Lower the second degree of the scale: in A minor, B becomes B♭.
2. Build a major triad on it: B♭–D–F.
3. Put its third, D, in the bass. That makes it a "sixth" chord, because the root, B♭, is a sixth above the bass.

In a minor key, D and F already belong to the key, so only B♭ is chromatic. In a major key the chord needs two borrowed notes: in C major, N6 is D♭–F–A♭.

What it does

The Neapolitan is a predominant chord (harmonic function): it leads to V, either directly or through a cadential six-four chord (i6/4–V). Its lowered second degree (B♭) usually falls toward the leading tone, either through the tonic (B♭–A–G♯) or straight down a diminished third (B♭–G♯). In four-part writing the bass note (D) is usually the doubled note, and B♭ often sits in the top voice.

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The name

The chord is associated with 18th-century opera composers working in Naples, although composers elsewhere used it as well, and earlier. In the Classical and Romantic periods it became a standard way to darken a cadence, especially in minor keys.

A connection to jazz

A dominant seventh chord on the same lowered second degree (B♭7 in A minor, D♭7 in C major) is the tritone substitution for V7. Jazz musicians reach the ♭II sound from a different direction, but the half-step slide down into the tonic is the same.

Practice with The Neapolitan sixth and Label the chromatic chords.