Diatonic chords are the ones which are built from the scale of the prevailing key. Chromatic chords use one or more notes which do not exist in the scale of the prevailing key. The word “chromatic” means “colour”, and chromatic chords make the music sound more colourful. Chromatic chords add beauty and harmonic interest to the music, but they do not create a key change (or “modulation”).
In a major key, there are seven diatonic chords, each built from the 7 degrees of the major scale.
In a minor key there are more diatonic chords, because we can use the notes taken from the ascending or descending melodic minor scales. However, in practice, most of the time we only use the chords with the raised 7th degree of the scale. This is where the name “harmonic” minor scale comes from – this scale contains the notes most often used for creating harmony.
In addition to these diatonic chords, a vast number of chromatic chords are available. Some of these have special names, such as the Neapolitan 6th chord. Some are chords which are borrowed from the key with the same tonic – for example a chord from A minor might be used within the prevailing key of A major. Some chromatic chords are simply triads which have one or two notes altered by a semitone. And another group of chromatic chords is the “secondary dominants”, which we will meet later on in this unit.
Voice-leading and Progressions
All chromatic chords normally move with chromatic voice-leading. This means that they move away from the previous chord and into the next chord by steps of a semitone within a part, rather than leaps.
Chromatic chords can either substitute a diatonic chord in a normal chord progression or they can be used as decorative chords which are “diversions” within a normal chord progression, in which case they are either passing chords or auxiliary chords.
An example of a chromatic substitution chord could be changing IV-V-I to iv-V-I, within a major key. Chord iv (chromatic minor subdominant) is substituted for IV (major subdominant). In C major the chord progression would be Fm-G-C.