Pentatonics on Two Strings

This lesson explains another mental model for navigating horizontally using the pentatonic scale. It expands on the approaches presented in the "only pentatonic scale lesson you will ever need" video and Playing Melodically on One String (Part 2). This approach requires adding two new shapes to your repertoire, but it opens up a lot of tasty licks!

Pentatonics on two strings¹

In a previous lesson, I presented a technique for navigating the pentatonic scale along one string, and I simplified that approach a little bit in Module 4 of Improv 101. While I am a huge fan of making melodies by playing pentatonic scales on a single string, there’s another technique for horizontal pentatonic movement that is well worth learning. It requires a small expansion of the rectangle and stack system, but it’s worth the slight increase in complexity.

When you lay a pentatonic scale out along two strings, the result is five quadrilateral (four-sided, four-note) shapes.² I’ve color-coded them in ascending order along the neck in light blue, red, dark blue, green, and orange.³

Here they are on an all-fourths fretboard (which ignores the warp):

The red rectangle shape is the familiar pentatonic rectangle from my rectangle and stack system. The two blue shapes are the lower (lighter blue) and upper (darker blue) parts of pentatonic stacks. I call the light blue shape the lower stack and the dark blue shape the upper stack. Here is that part of the diagram isolated to show the full stack shapes:

The other two shapes come from the spaces between rectangles and stacks when we alternate them vertically:

If we fill in the empty spaces, we get the green lower trapezoid and orange upper trapezoid shapes:

When a rectangle is below a stack, there’s a lower trapezoid between them:

And when a stack is below a rectangle, there’s an upper trapezoid between them:

When laid out horizontally, the five shapes form a repeating sequence: lower stack, rectangle, upper stack, lower trapezoid, upper trapezoid. This diagram shows the A minor (or C major) pentatonic scale on the B and E strings:

These shapes work on any pair of strings, but when they overlap the warp, they are distorted. This is the E minor (or G major) pentatonic scale on the G and B strings:

One of the biggest “gotchas” about the warped versions of the shapes is that the lower trapezoid and upper trapezoid each look like the other. So watch out for that!

One of the best uses of these shapes is to play a melodic sequence in one shape and then move either up or down the fretboard, repeating that melodic sequence inside each shape. Here’s an example of that in A minor moving up the fretboard:

Here’s a descending lick using the same shapes:

I recommend practicing sequences like this on each pair of strings.

To incorporate these patterns into an improvised solo, you’ll need to practice switching between mental models. If you’re playing one of the five standard pentatonic “forms” or “boxes,” and you’re familiar with how they are broken down into rectangles and stacks, it’s pretty easy to identify all five of the two-string patterns inside the fingering pattern, so you can pick any of them and start moving horizontally from there. The same is true if you’re using one of the diagonal pathways made out of stacks.

After you’ve played horizontally for a bit, you may want to switch back to playing along a diagonal stack pathway or in one of the familiar pentatonic forms. There are a few helpful landmarks you can learn for this.

We’ve already seen how the full stacks surround the rectangle, building off of the lower stack and upper stack shapes:

Similarly, we can easily find stacks connected vertically to the short edges of each trapezoid:

And finally, we can also find rectangles connected vertically to the long edges of each trapezoid:

These two-string pentatonic patterns are a great mental model to have in your bag of tricks. Enjoy!