There are 7 different notes in a major scale. There are 12 different notes in an octave. So in any major scale there are 5 notes that are not played. (12-7=5) The 5 unplayed notes rest between the notes that are played. There is a subtle but very interesting relationship that can be shown between the notes that are played and the notes that are not played.
The notes (and chords) for the C major scale are:
Cmaj7-Dm7-Em7-Fmaj7-G7-Am7-Bm7b5-Cmaj7
The 5 unplayed notes (Db-Eb-Gb-Ab-Bb) form the pentatonic (Ebm) relative minor scale of Gb major. Likewise, the notes (and chords) for the Gb major scale are:
Gbmaj7-Abm7-Bbm7-Bmaj7-Db7-Ebm7-Fm7b5-Gbmaj7
These 5 unplayed notes (G-A-C-D-E) make up the pentatonic (Am) relative minor scale of C major.
(This is where you pause, stroke your chin and go "Hmmm….")
This relationship alone is quite interesting. The 5 unplayed notes in each major scale is the pentatonic relative minor scale for the other key!
Now, starting with C, combine all of the chords from both scales sequentially:
Cmaj7-Db7-Dm7-Ebm7-Em7-(Fm7b5/Fmaj7)-Gbmaj7-G7-Abm7-Am7-(Bm7b5/Bmaj7)-Cmaj7
Notice that the subsequent progression fits together rather nicely and makes for some very nice transitions from one chord to the next traveling either up or down.
The only two notes common to both keys are F and B, which are also separated by the same interval (#4/b5) as C and Gb. That F is Lydian in the key of C and Locrian in the key of Gb, and that B is Lydian in the key of Gb and Locrian in the key of C also points to another interesting and useful relationship.
Plus, the 5th chord from each scale (G7/Db7) if played as its alt. version, that is G7#9 and Db7#9, becomes what is called a "Neopolitan" 5th for the other key.
Thus we glimpse yet another potential way to use every single note when writing songs, soloing, changing keys, moving from one chord to another, etc.
Now run along and play nicely children . . . . . .
Things only seem difficult until we find a way of thinking about them that makes them seem easy.
Guitar Jazz