I've been working on the changes to "All the Things You Are." The key of the tune modulates through Ab, C, Eb, G, E. I practice by cycling through the major scale for each key, and this helps with accessing arbitrary scales all over the fretboard.

Within each key is a diatonic collection of chords moving up by fourths. A vi-ii-V7-I-IV progression occurs twice in Ab, once in Eb. I wondered how I could adapt the tonic major scale of the key to navigate through these changes. My usual approach has been to use the arpeggio of each chord as an anchor for my improvisation. That has always been a challenge to remember so many different shapes as they go by often quite quickly. So I worked out a system of pentatonic scales over each chord. Minor pentatonic (1 b3 4 5 b7) is used over m7 chords. Major pentatonic starting on the 5 (5 6 7 2 3) is used over maj7 chords. Dominant pentatonic (1 2 3 5 b7) is used over 7 chords.

Here's how it works out in Ab:
vi - Fm7 - F minor pentatonic - F Ab Bb C Eb
ii - Bbm7 - Bb minor pentatonic - Bb Db Eb F Ab
V7 - Eb7 - Eb dominant pentatonic - Eb F G Bb Db
I - Abmaj7 - Eb major pentatonic - Eb F G Bb C
IV - Dbmaj7 - Ab major pentatonic - Ab Bb C Eb F

Note that only one note changes between each scale, and Eb and F are common to all of them. Rearranged to illustrate:
vi - Eb F Ab Bb C
ii - Eb F Ab Bb Db
V7 - Eb F G Bb Db
I - Eb F G Bb C
IV - Eb F Ab Bb C

Now that's far easier to remember than the arpeggio for each chord. I'm getting that cycle of pentatonics under my fingers for each major scale position. When I switch keys in a tune like "All the Things," I only have to find the tonic major scale and visualize the changing pentatonics over it as a guide through the changes.

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