COMMON TONE CHROMATIC MEDIANT CHORDS

Before explaining the common tone chromatic mediant chords, we shall first explore chromatic mediants.

Chromatic mediants

A chromatic mediant is a relationship that can exist between two chords or two keys. 

Two major triad chords or two minor triad chords are chromatic mediants of each other when their roots are a third apart (either a major third or a minor third). 

For instance, the C major triad chord has following chromatic mediants: the Ab major triad chord, A major triad chord, E major triad chord and Eb major triad chord. This is shown in the next figure. Each chromatic mediant chord has a single note in common with the original chord. The common notes are shown in red in the figure. When a descending major or minor third is used, this results in lower chromatic mediants. When an ascending major or minor third is used, this results in upper chromatic mediants. Thus, the Ab major triad chord and A major triad chord are lower chromatic mediants of the C major triad chord, while the  E major triad chord and Eb major triad chord are upper chromatic mediants of the C major triad chord.

Figure: The chromatic mediants of the C major triad chord (the common notes are shown in red)

The next figure shows the chromatic mediants of the C minor triad chord.

Figure: The chromatic mediants of the C minor triad chord (the common notes are shown in red)

Similarly, two major keys or two minor keys are chromatic mediants of each other if their tonics are a third apart (either a major third or minor third). For instance, the C major key has following chromatic mediants: the Ab major key, A major key, E major key and Eb major key while the C minor key has following chromatic mediants: Ab minor key, A minor key, E minor key and Eb minor key.

Annotating common tone chromatic mediant chords

The next figure shows the beginning of Chopin's Polonaise-Fantaisie Op. 61. 

Figure: The common tone chromatic mediant chords in the Chopin Polonaise-Fantaisie (common tones are marked in blue)

At the beginning of measure 2, we see two chords that are chromatic mediants of each other. They are major triad chords whose roots are a minor third apart and have one common tone: Db. The common tone is marked in blue.

Similarly, at the beginning of measure 8, we see another two chords that are chromatic mediants of each other. Again, they are major triad chords whose roots are a minor third apart and have one common note: Ab. The common tone is marked in blue.

In the figure, we see the annotation for common tone chromatic mediant chords that is used in this book: a horizontal line labeled with “CT” which connects the chords.