Pentatonic Scale Harmony

Most players are at least vaguely familiar with pentatonic scales.
They're used in all kinds of music all over the world.
Jazz players often use a pentatonic scale as a melodic device, but overlook its harmonic possibilities.
Since this scale isn't entirely made up of steps, some interesting voicings result from harmonizing it.
One reason for pentatonic scales' popularity is that they can be used over many different tonal centers
without too many "avoid notes", notes that sound bad against a chord.
This property of the scales also makes them useful for comping.

For our purposes, let's examine the A minor pentatonic scale (A-C-D-E-G).
Many of us first encountered this scale in a rock or blues context;
it has many other potential applications!

First, let's harmonize the scale in 3-note voicings:

Note how we automatically get triads interspersed with "cluster" voicings. Cool.
The sound of those close intervals may take some getting used to.
Bar 1 is in root position; bars 2 + 3 are 1st and 2nd inversions.
In the last bar, I spread the voicings from the first group:
I moved the middle voice up to the top (and also moved the whole voicing down an octave).
All the inversions could be spread-voiced as well; try it...

Here are some playable 4-note voicings.

Analyze all these voicings; most of them could be used in many ways!
For example, the 2nd voicing shown could be used as:
F6/9, Am7sus4, Dm7sus4, Bbmaj13, C6/9, F#7alt, Gm9sus4, and a few other things!

Below is a table showing several chords to which the A minor pentatonic scale can be related:

Am root 3rd 4th (11th) 5th 7th
C, C7, C9,etc. 6th (13th) root 2nd (9th) 3rd 5th
Gm 2nd (9th) 4th (11th) 5th 6th root
Dm 5th 7th root 2nd (9th) 4th (11th)
D7sus4 5th 7th root 2nd (9th) 4th (11th)
F 3rd 5th 6th 7th 2nd (9th)
Bb 7th 2nd (9th) 3rd #11 6th
F#7alt #9th b5th #5th 7th b9th

There are others, but this'll do for now.
Of course, it'd be pretty tough to memorize this table, so here are a few hints.
You can use this pentatonic scale harmonically just as you might use it melodically:

A Few Hints:
On a minor chord, you can use a minor pentatonic scale starting from the chord's root, 2nd, or 5th.
On a major chord, you can use a minor pentatonic scale starting from the chord's 3rd, 6th (or 7th for a Lydian [#11] sound).
On an unaltered dominant 7th chord or 7sus4, you can use a minor pentatonic scale starting from the chord's 2nd, 5th or 6th.
On an altered dominant 7th, you can use a minor pentatonic scale starting from the chord's #9.

Okay, let's look at some musical examples now.
In the first couple of examples, we'll continue to use the A minor pentatonic over a set of changes.
Then we'll get into mixing and matching different minor pentatonics using the guidelines above.
In example 1, we have a common ii-V7-I progression, all handled with the A minor pentatonic scale.

Notice the ambiguous, "open" sound a lot of these voicings have.
Many of these voicings lack "guide tones", which is OK in a group context; someone else'll likely be playing the guide tones.
In real life, you'll probably find this pentatonic approach most satisfying when mixed with other types of voicings.
Too much ambiguity can get tedious eventually...

Example 2 is a I-IV-iii-VI progression in F major. Note the #11 sound on the IV.
Again, we're using only voicings from A minor pentatonic.


Now we're going to start using voicings from more than one minor pentatonic scale.
I've labeled the scale choices; check them against the "hints" above to see how I chose the scales.

Example 3:


In spots where the harmony doesn't change much, using alternate pentatonic choices can liven up the sonic landscape.
In example 4, I used Dm, Em and Am pentatonics to play over a long stretch of D minor.
(This example's not too interesting rhythmically; I wanted to cram in a lot of voicings!)
Try voicings like this next time you play "Impressions" or "So What".

 "But, Bob," I can hear you saying, "don't all these voicings exist in the C major scale?"
Well, sure they do, but what makes them sound different is that we're leaving out certain notes in the major scale,
or, more accurately, choosing to concentrate on only some of the notes at a time.

As I implied earlier, I doubt I'd play a whole tune using nothing but pentatonic harmony,
but this method can open up some interesting sounds.
Used judiciously, it can provide a nice contrast to tertian [third-based] harmony.