In Part 2, Chuck Anderson provides more about the foundation of harmonics as the Jazz Guitar Improvisation Lesson Series continues.
We have looked into Full Diatonic major and minor relationships. These are on the charts
After Full Diatonic is Internal Modulation
This is a temporary key change. It requires a minimum of 2 chords in the new key. There is a minimum requirement of one Active ( V, IV, II, and VII) and one Passive (I, VI and III) chord in the new key. You can typically recognize the Internal Modulation by locating a 7th chord outside the original key and tracing it to the V column on your Full Diatonic charts. The V chord will suggest the new key. Confirm that the chords around the V are members of the new key. When the progression returns to the original key, the Internal Modulation is over.
It’s possible that a progression will move into multiple keys before returning to the original key. It will ultimately return to the original key. Look at All the Things You Are as an example. The original key is Ab. It then moves by Internal Modulation into the key of C, Eb, G, and E. Find Internal Modulation in as many songs as you can.
Internal Modulation Expanded
If an Internal Modulation begins on any Active chord such as II, IV or V, it is a Prepared Internal Modulation. The Active chords “set up” the temporary key shift for the ear.
Most Internal Modulations are Prepared. If an Internal Modulation begins on any Passive chord such as I or VI, it is an Unprepared Internal Modulation. The Passive chords do not “set up” the temporary key shift for the ear. An example is the first chord of the Bridge in Girl from Ipanema.
Both forms of Internal Modulation are treated the same way but this distinction helps to organize and categorize the two forms of Internal Modulation. Not only is it helpful in analyzing songs, but it’s also a good technique for writing chord progressions.