In a basic 12 Bar Blues, there are usually three different chords. Each of these relates to one basic Key. In Blues, the most common chords are those built on notes 1, 4 and 5 of the major scale. So in the key of C, these chords would be C, F and G. In the Key of A they would be A, D and E. Example 249 demonstrates the 12 Bar Blues progression played with a movable shuffle pattern in the key of A. The first and third fingers remain on the strings, while the fourth finger stretches up two frets on the same string as the third finger.
A shuffle pattern can be played in any key simply by moving its root note to the appropriate fret. The following example is in the key of G in the 3rd position (3rd fret).
The following diagram shows the 12 Bar Blues progression in Roman numerals I, IV and V instead of 1, 4 and 5. In this case, the Roman numerals refer to chord numbers within a key, rather than positions on the fretboard. The C symbol is a bar repeat sign (repeat the