Superimposing new chord progressions onto the structure of a song is extremely important in improvisation. What you are basically doing is adding new chordal structures to give the tune more variety. It may seem that in doing this you are taking the given chord structure and changing it, taking away from what the tune is about; but in superimposing you don’t change the primary chords, you simply add to or vary the chords that approach the primary chords. I call these added chords secondary chords. Each time you play a chorus of a tune, you can vary the secondary chords to give your solo a fresh sound. It is very important to remember, though, that when you add these chords you should have it worked out with the bassist and guitarist so you won’t sound like you are out in left field.
I will use the basic 12-bar blues progression as my example, since everyone should be familiar with the form and the changes. Here are the primary chords in the progression (Ex. 1):
Now compare the primary progression with this reconstructed progression, in which superimposed chords add color and variety (Ex. 2):
The above example may seem a bit over-constructed, but I wanted to show a variety of possibilities that you can experiment with. Also, it has many two-chord-to-the-bar situations. A good way to begin learning to improvise over these changes is to play scale fragments (Ex. 3):
I have shown the root-2nd-3rd-5th fragment for each chord; you can try some other possibilities for yourself. Even using just this fragment, you may want to alternate between ascending and descending versions, which will vary both the sound and the melodic movement (Ex. 4):
Here is another version of the 12-bar blues progression (Ex. 5):
In this blues progression, two of the primary chords (compare with the original blues progression) have been altered. Fm9 is substituted for C7 because of the descending sequence in bars 6, 7, and 8; and Dm9 and G13 are substituted for G7 and F7 to give this particular progression a llm9-V13-I cadence. This progression has a nice flow and is fun to improvise over. If you are improvising three choruses of a blues, it sounds great to play the progression shown above on the second chorus to give the solo a fresh sound and add some new color. On the third and final chorus, you can go back to the original blues progression to bring it back to home base. Here is another option (Ex. 6):
Remember that these are just three examples of what can be done to add color and variety to a basic progression. This is in no way designed to take away from the beauty and simplicity of the blues. It’s just a way of giving the soloist a new vehicle to build new sounds and directions for his or her solo.