Omitting Unavailable Tensions
In the previous lesson on Available Tensions, we established that not all notes in a chord are of equal importance.
- The 3rd and 7th of a chord (called Guide Tones) are the most harmonically important notes because they establish the quality of the chord (i.e. whether it’s a Maj7, m7, V7, etc.);
- The root and the 5th of a chord are relatively less important;
- The 9th, 11th, and 13th (called Tensions) are even less important.
In Jazz you don’t always need to play every single note in a chord. It’s common practice to omit any unavailable tensions from a chord. For example, a CMaj13 chord and a C13 chord (both of which you will come across in practice) both implicitly omit the ♮11 because it is an unavailable tension or avoid note. So:
- CMaj13 = C E G B D ( ) A
- C13 = C E G B♭ D ( ) A
Shell Chords
We also learned that each main type of 7th chord has a particular ‘feel’.
| Chord | Feel/Sound |
|---|---|
| CMaj7 | Happy or calm |
| C7 | Tense |
| Cm7 | Sad |
| CmMaj7 | Confused sadness |
Well, it’s possible to omit the less important notes (root & 5th) from a chord and only play the guide tones (3rd & 7th) and still retain the original ‘feel’ of the chords. So for example, you could play a:
- CMaj7 – as just E & B
- C7 – as just E & B♭ (a tritone interval)
- Cm7 – as just E♭ & B♭
- CmMaj7 – as just E♭ & B
This is called a shell chord (because it’s only the shell of the whole chord). Shell chords are important because they represent the minimum harmonic material (i.e. notes) needed to play a chord. Any chord voicing should generally include the 3rd and the 7th of the chord; without these the chord will sound incomplete.
Playing a II-V-I in the key of C Major using shell chords would look as follows:
Notice how smoothly each chord transitions to the next. Only one note needs to move to get from Dm7 to G7 and to get from G7 to CMaj7. This is one of the advantages of shell chords – their simplicity.
Playing shell chords has the following advantages:
- As I mentioned above, they are simple – after all, you’re only playing 2 notes;
- It sounds harmonically strong because you’re emphasising only the two most important notes;
- By playing so few notes you ‘create space’ for the soloist (or your right hand) to play a faster and more harmonically complex improvisation. A solo is less likely to clash with the harmony if the harmony has fewer notes.
Chord Ambiguity
A topic we will run into many times in the course of these lessons is that of Chord Ambiguity. Shell chords, because you are playing so few notes, are ambiguous. Playing two notes could indicate a number of different shell chords. For example, playing B & F could be a G7 (3rd & 7th) or D♭7 (7th & 3rd). And the only way to know whether the shell chord is a G7 or a D♭7 is to look at the next shell chord. If the next shell chord is B & E (CMaj7) then the prior chord was a G7; whereas if the next shell chord is B♭ & F (G♭Maj7) then the prior chord was a D♭7. We will explore this further in the next lesson on Chord Substitution.
In Practice
Bebop pianists (circa 1940’s) like Bud Powell used shell chords when accompanying themselves or a soloist. This is because Bebop solos are fast and complex, so the chords had to be simple and sparse to stay out of the soloist’s way. Bud also added a root note to shell chords to establish the tonality of the chord (CMaj7 = C E B).
We will come across the idea of omitting the root and/or 5th of a chord again in later lessons, when we discuss Rootless Chord Voicings and Bud Powell Voicings.