What To Know About Quartal Harmony and the Tritone Substitution

Quartal Harmony and the Altered Dominant Sound

Although playing the C major shapes over a ii7 – V7 – I progression sounds great, it only produces the unaltered notes in relation to the V7 chord. In jazz, the sound of the altered 7 is often desired for more colorful harmonic movement. I have two main methods that I like to use to achieve this sound. The first is by applying the quartal harmony shapes of the 7th mode of the melodic minor scale. This strategy is covered extensively in this JGT article by Zakk Jones:

Because I am more familiar with the major modes and their quartal shapes, I find I can usually be more creative when I use the tritone substitution to create the altered sound. With the rest of this article I will be discussing this second method, its uses, and applications.

Using the Tritone Substitution

If you are not familiar with the concept of the tritone sub, you can check out a great explanation from Chuck Anderson HERE.

Often when students learn about the tritone sub they are taught how to apply it within a single line or tertian harmony framework. When applied to quartal harmony, this concept creates some incredibly useful, altered voicings. Instead of using our C major / G mixolydian quartal shapes to outline a G7 chord, we will now use out Gb major / Db mixolydian quartal shapes. That gives us these notes in relation to the G bass note.

Our only problem note is the F#. Even though the major 7 shouldn’t theoretically sound good over a dominant chord, the strength of the quartal shapes and the tension created by the other notes allow it to work great!

When we encounter a ii7 – V7 – I progression, we can now approach it like this:

Rhythm Changes Etude

Below is a rhythm changes comping etude to help demonstrate the concept. Because the ii7 and V7 are interchangeable, when I encounter short ii7 – V7 progressions I often think of the whole measure as the V7 chord as shown in measures 16-20. I also like to occasionally treat the entire first four measures of the A sections as an altered dominant like in measures 41-43.

In these examples, I almost exclusively use quartal voicings. They are meant to show you how they can be employed over functional harmony to open things up sonically. When I am in actual performance situations, I tend to mix up the type of voicings I use a bit more. In many cases I even surround them with tertian harmony to disguise the intervallic sound. As you work out your own ways to blend your voicing types, you will develop your own unique style.

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