Here’s another chordal embellishment to the 12-bar form: In measure six, insert a diminished chord based on the #4 of the key. Fig. 8 shows measures five through seven of the 12-bar form with this snazzy enhancement.
Let’s put it all together. Fig. 9 includes all of the embellishments we’ve examined so far. To add some harmonic variety, I’ve included 13th chords in this example.
Fig. 10 brings us to the tritone substitution. Without going into great theoretical detail, the tritone substitution replaces one chord with another that has its root located a tritone (three whole-steps) or b5 away. It doesn’t matter whether you count up or down to get to the b5 because a tritone splits an octave exactly in half. In the following example—used over the last four measures of the 12-bar form—C13 is the tritone substitution for F#7 (VI), and Bb13 is the tritone substitution for E7 (V).
“Stormy Monday” Changes
A survey of common 12-bar blues progressions would not be complete without the inclusion of the “Stormy Monday” changes. The classic T-Bone Walker tune is a must-know, and the progression in Fig. 11 shows how it’s most commonly played. The most notable difference between this progression and the basic 12-bar blues occurs in measures seven and eight with the ascending and descending minor chords. For variety, I’ve written this example in the key of G and included 9th chords.
Blues guitarists frequently use chromatic approaches when performing this piece. For more details on this concept, as well as musical examples that illustrate it, check out “Uptown Blues,” another lesson in PG’s Style Guide series.