One of my favorite ways to generate harmony is to take two chords and stack them on top of each other. This is usually referred to as polytonal harmony, upper structures, or in my parlance, chord stacking. This requires another musician or a recording device. Two things about this type of harmony appeal to me: 1) how easily close-voiced chords are created, and 2) one doesn’t have to memorize hundreds of different voicings of chords. Instead, take the major and minor triads you already know a learn how to use them with other triads. The concept is straightforward but the applications are profound and virtually limitless.
If we look at the anatomy of chords we can sometimes find buried within them two different chords. Let’s use the chord C major 9 as an example.
• C major 9 = C, E, G, B, and D
• The chord C major = C, E, and G
• The chord G major = G, B, and D
Therefore, if someone is playing a C major chord and I play a G major chord at the same time the resulting harmony will produce a C major 9 sound. We can think of it in terms of chord numbers too:
• A V chord stacked on top of a I chord will yield a major 9 chord. This could be written as a fraction:
• V/I = major 9
Here are a couple more formulas for generating harmony:
• -v/-I = minor 9 (example: B-/E- = E minor 9)
• -v/I = Dominant 9 (example: G-/C = C9)
• V/-vi = minor 11 (example: G/A- = A minor 11)
Piano players use this all the time but I don’t run into many guitar players that use it. Therefore, I’ve included it in the guitar section of the website but the concepts are equally viable with piano. I imagine it’s prevalent in the jazz-guitar world but not so much in other styles. (Or perhaps I just need to get out more.) Most often this technique is used to generate altered sounds and it works wonderfully. But to me the most satisfying sounds come from non-altered chords (major 9’s, minor 9’s, and minor 11’s). That’s just my ears talking. Your ears might tell you a different story. Here are a couple of guidelines that I follow when playing:
•it’s usually a good idea to put the root chord in a lower register than the stacked chord. Example: G over C for a C major 9, not the reverse. But do what you think sounds best.
•use only the simple major and minor triads when stacking chords.
Accompanying these words is an excerpt from my personal polytonal sketchbook. Over the years I’ve jotted down ideas during practice as they’ve come to me. Some were great and some were not. This particular page shows a few possible ways to use this harmony when playing a ii – V – I chord progression in the key of A major: