The chromatic chords
A reference card. Beyond secondary dominants and borrowed chords, there's a small family of chromatic chords — spicy, dramatic harmonies that use notes from outside the key. They're the vocabulary of Romantic opera and the big emotional moments. Recognise them; you don't need to build them yet.
The Neapolitan sixth
A major triad built on the ♭2 of the key, almost always in first inversion (so ^4 is in the bass — hence "sixth"). In A minor, that's a B♭ major chord. It appears just before the dominant, adding a dark, fatalistic weight to a cadence.
- Written ♭II6 or N6.
- The tell: a ♭2 appearing in a chord, not resolving up.
The augmented sixth chords
Three related chords, all containing the interval of an augmented 6th (which sounds like a minor 7th but is spelled to splay outward to an octave). Named by nationality for no particularly good reason:
| Name | Extra note above the basic shape | Flavour |
|---|---|---|
| Italian sixth (It+6) | just the three notes | lean, stark |
| French sixth (Fr+6) | + a ^2 | shimmery, Impressionist |
| German sixth (Ger+6) | + a ♭^3 | rich, Wagnerian |
All three drive powerfully to the dominant. They're a Romantic-era favourite for the moment before a big arrival.
The diminished seventh as a pivot
The fully diminished 7th chord (Movement H, the other seventh chords) is symmetrical — stack of minor 3rds — so it belongs to no single key. That makes it the ultimate pivot chord: a composer can spell it one way, then re-spell it and resolve it into a completely distant key. It's how a lot of dramatic key changes happen.
Where you land
For Stage 4: if you see a ♭II (Neapolitan), a +6 (augmented sixth), or a diminished 7th being used to swing into a far-off key — recognise it as Romantic chromatic harmony, know it's heading to the dominant or pivoting somewhere, and read on. Building and resolving these properly is a later harmony stage.