If we’re going to ask this question, we’re going to have to talk about the chords of the E flat major scale. If you are familiar with the history of the major scale, you’ll have already guessed that the A major scale is basically an inverted E flat major. The shape that this scale takes is the shape of an 8th string. It has the same notes — a B♯ major root note — but it takes up half of the string. What this means is that the A major in E flat major is the same shape as the A major in major triads. And the E flat major is almost exactly the same as the E minor, though it takes up the last half of the string.
This means we can make an analogy to make things easier
Imagine we have a guitar, and we want to play all the chords in our solos, so that we can play an A minor root note chord like “G4 B5 5.6,” and we want all the other chords to be A minor and minor (see example above, or see the E flat minor above, so they look just like the B♭ major chord). This is like playing a C major on the B♭ major scale. The C major scale would look like this:
And here’s an approximation of a D major scale:
Notice the shape of the D major scale is a pentatonic, and it doesn’t look like E flat major. A minor triad looks like this:
And our C major looks like this:
If we replace “G4” with “A,” we get a C minor and minor C major scale. Now the E flat major sounds like the same shape, it just takes up half the string. It’s just a minor pentatonic.
In fact, that C-sharp chord that has the chord tone of the C major scale, as well as the interval of 2nd, 3rd, 4th and 5th, is a “minor pentatonic,” and this is the most common form of minor pentatonic in western music.
Here’s a chord progression that uses the E flat major in a minor scale structure:
I’ve also included the D minor scale, which is the most common form of D minor pentatonic in western music. And since we’re using these chords and other minor pentatonic shapes, we can learn how you can substitute any chord or scale in your next