If you play through the three 12 Bar Blues examples given in this lesson, you will see a pattern being formed. This pattern, (following diagram), represents the starting note for each riff of the 3 chords in the 12 Bar Blues.
The root note is the note with the same name as the key of the Blues, e.g., for a Blues in the key of A, A is the root note.
This 12 Bar Blues pattern can be played by starting on any fret of the 4th string. The note you start on will be the root note, indicating the key of the Blues, e.g., If you start at the 6th fret, a Bb note, you will be playing a Blues in the key of Bb.
This pattern can also be played on a 3rd string note, as such:
This variation is more convenient for keys such as E, i.e., starting on the 7th fret of the 3rd string rather than the 12th fret of the 4th string.
Using Blues pattern one you can now play a 12 Bar Blues in any key.