By: Joseph Alexander
The most important substitution to get under your fingers when learning how to play jazz guitar, is the tritone substitution, which is what we will explore in this instalment of my 10-part series on Drop 2 Chords.
In its simplest form, this is the substitution of the original dominant chord for another one three tones (hence tri-tone) away.
The distance of 3-tones in music is a flattened 5th or b5, and so the terms tritone substitution and b5 substitution are synonymous.
Staying with the ii V I progression in C Major, the original dominant chord is G7.
The tritone substitution on the b5 is therefore a Db7 chord.
Something very interesting happens with the guide tones (the 3rd and b7 of each chord) in a tritone substitution, which you can see in the table below.
|Chord Tones of G7||G||B||D||F|
|Chord Tones of Db7||Db||F||Ab||Cb (B)|
Look at the guide tone notes (3 and b7) in both chords.
Can you see that in each chord the 3rd has become the b7 and the b7 has become the 3rd?
In fact it is a rule of music that when you substitute a dominant chord for another dominant chord three tones away from the original, the two chords will ALWAYS share the same guide tones.
Why is this important?
As you may know from soloing or comping, the two most important notes and defining intervals of a chord are the 3rd and the 7th. The 3rd tells you if the chord is major or minor and the 7th tells you which kind of major or minor chord it is.
If you target those in our playing, your soloing will always closely outline the harmony that you are soloing on.
Not only that; if you strongly emphasise the 3 and b7, you can pretty much get away with any amount of tension in the melody as long as we melodically resolve our phrases.
All of this means that soloing or comping the tritone substitution is a very concise way to ‘stick to the changes,’ whilst adding in some beautiful creative tensions.
Analysis of the Tritone Substitution.
Let’s look at the intervals formed when you play the tritone substitution Db7 over our original bass line of G7.
|Chord tones of Db7||Db||F||Ab||Cb (B)|
|Interval formed against G bass note||b5||b7||b9||3|
The above table shows that if we play a Db7 chord over a G bass line, the resultant harmony is G7b5b9.
Ok, enough chitchat!
The next example shows the Drop 2 Chords for Db7 on the top four string.
And here are those Drop 2 Chords substituted into the ii V I in C major.
Study the voice leading in each chord change carefully from the above example.
Notice that every note except the B moves down by a semitone between Db7 and Cmaj7, the B doesn’t change.
The tritone substitution is one of the main ways that you can produce chromatic voice leading when playing in a chord melody style.
It’s also an extremely useful device to reinforce a jazz melody in the rhythm part when the notes are chromatic to the chord.
Drop 2 Chords Extensions
You can also extend the tritone chord as far as you like away from the original Db7, for example using Db9, Db13 etc.
You can also add altered extensions too, such as D7b9, D7b13 etc.
An interesting quirk is that natural extensions like 9s and 13s make the substitution more dissonant from the original chord of G7, whereas altered extensions like the b9s and b13s make the chord less dissonant against the G7.
Your homework today is to extend the Db7 chord to a Db9 chord and insert it into the major ii V I progression.
We used a similar approach with G7 in lesson 3 of this series, so you should already have the chord shapes ‘down’.
Notice how the natural 9th extension becomes a #5 (b13) against the original chord root of G.
When you are comfortable with that, try doing the diminished 7 sub from lesson 2 to create a Db7b9 instead of the Db7 chord.
Now notice how the b9 of Db becomes a natural 5th of the underlying G harmony. Do this in all four positions.
About the Author
A professional guitar teacher for over 12 years, Joseph Alexander graduated from The Guitar Institute in London with a Diploma in Popular Music Performance. He continued his education at the prestigious Leeds College of Music achieving a BA (Hons) in Jazz Studies in 2002. He currently lives in Poynton, England and is busy teaching a new wave of upcoming guitarists and is the author of the eBook Fundamental Changes in Jazz.