Hi,
This post is an attempt to understand basic chords substitution.
This is useful when the chords for both the verse and chorus of a song are the same.
Let's list down the chords in G major.
I II III IV V VI VII
Gmaj7 Am7 Bm7 Cmaj7 D7 Em7 F#m7(b5)
For example, the chords of a song uses I VI IV V progression.
The chords will be Gmaj7 Em7 Cmaj7 D7.
We can substitute I with III.
Instead of playing Gmaj7, we change to Bm7.
The new progression will be Bm7 Em7 Cmaj7 D7
The notes in a Gmaj7 are G B D F#
The notes in a Bm7 are B D F# A
Out of 4 notes, 3 are the same, therefore it will sound correct.
Hope this helps.
Have fun.
