Chord Substitution - Part 2 - Flat Five Substitute
Continuing our discussion of chord substitution, we will look at the flat five substitute. This is often used to break up overly cyclic, (moving in fourths), chord progressions, to change the bass line of the progression, or to approach a chord from a half step above, in order to add more motion to a progression, (or solo). It is an easy to apply substitute, once you know how it works, and can help add a lot of interest to your chord progressions or solos.
Start by taking any dominant seventh chord, in this example, G7. A dominant seventh chord as you may recall, consists of the 1, 3, 5, and 7b of the Major scale of the same name. This would give us a G, B, D, and F for a G7 chord. Next, take the fifth, D and flat it. This is the root of your flat five substitute. For G7 then you can substitute a Db7 chord. Most of the time you will use a dominant seventh chord, but the melody may suggest an alternative, and remember that melody is always the most important guide to your choices.
How does this work? Take a look at the notes contained in each chord. In G7 you have G, B, D, F, and in Db7 you have Db, F, Ab, and Cb. Relating this to the G7 chord, the Db is of course the flat five, the F is the seventh, the Ab is the flatted ninth and the Cb, (B), is the third, giving us a G7-5-9 chord without the root. So in essence, you are substituting an altered G7 chord, sans root, and with a different bass note.
In a typical II, V, I progression in the key of C you have Dm7, G7, going to Cmaj7. Applying our flat five substitute, we get Dm7, Db7, going to Cmaj7. Notice how this changes the bass line from the typical down a fifth, to a chromatic bass line, approaching the Cmaj7 from a half step above. You will also notice how this increases the tension leading into the Cmaj7 chord, giving the chord progression more motion.
You will get the same type of result if you use this kind of thinking in your solo. Using a scale that suggests a G7-5-9 over a G7 chord will give your line a lot more momentum going back into the C Major scale. This also gives you that "outside" sound that you hear a lot of players get. Creating tension in this manner when done tastefully can really give your solo lines a lot of power.
It is also possible to put this substitute in as a half step approach, keeping all of the original chords. Taking the same progression, we can see an example of how this would work. Start with your chords, Dm7, G7 and Cmaj7, but this time, take the flat five substitute for Dm7 and put it in between Dm7 and G7. This gives us, in common time, three beats on Dm7, one beat on Ab7, four beats on G7, and four beats on Cmaj7. Or take it a step further with three beats on Dm7, one beat on Ab7, three beats on G7, one beat on Db7, and four beats on Cmaj7.
This can be done in any combination that you want, and with altered or extended versions of the substitutions. Often the melody will suggest the alteration, or possibly a minor version of the substitution. That is why you should always look at the melody before making your final decision. When soloing and using this concept, you often have more flexibility in this area, but remember the number one rule of music, it has to sound right.