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Rhythm Changes
In 1930 George Gershwin wrote a song called "I Got Rhythm". Since then countless jazz compositions have been made that use the chord progression of that tune in one of its many modifications. The chord progression is known as Rhythm Changes.
Rhythm changes started to be popular in the swing era, but got even more popular in the bebop era. Lots of new themes were written over this chord progression (a new theme makes a new tune, so no royalties had to be paid to Gershwin). Compositions like this are called contrafact or heads. Here are some examples of Rhythm Changes:
Rhythm Changes are a 32-bar chord progression in the AABA form. They can be quiet daunting to improvise over because they are played very fast most of the time. Here's the basic progression:
|Bb Gm7 |Cm7 F7 |Bb Gm7 |Cm7 F7 |
|Bb Bb7 |Eb Ebm |Bb Gm7 |Cm7 F7 |
|Bb Gm7 |Cm7 F7 |Bb Gm7 |Cm7 F7 |
|Bb Bb7 |Eb Ebm |Bb F7 |Bb |
|D7 | |G7 | |
|C7 | |F7 | |
|Bb Gm7 |Cm7 F7 |Bb Gm7 |Cm7 F7 |
|Bb Bb7 |Eb Ebm |Bb F7 |Bb |
The basic building block of the A part of a rhythm changes is a simple diatonic I - VI - II - V progression. In bar 5 the Bb7 introduces the IV in the 6th bar. The IV changes to a IVm.
Chances are that the tempo in which you are playing Rhythm Changes is very high, so you may want to keep it basic. Here's how to keep it basic on the A part:
Make sure you outline the harmony in the 5th and 6th bar. Important notes are the b7 of Bb7 and the b3 of the Ebm. There's a chromatic guide tone line going from the Bb to the Ebm that outlines what is happening harmonically (the orange notes in the following example): 
Here's a variation of the A part that was popular in the swing era:
|Bb B°7 |Cm7 C#°7 |Dm7 G7 |Cm7 F7 |
|Bb Bb7/D |Eb E°7 |Bb/F G7#5 |Cm7 F7 |
Here's what happens:
- The Gm7 in bar 1, 3 and 7 is substituted by G7
- Bar 1: the G7 is substituted by B°7 (=G7b9) to get the chromatic line to Cm7
- Bar 3: the Dm7 is the II of G7
- Bar 2: the C#°7 is in fact A7b9 (the V of II) and continues the chromatic line initiated in bar 1
Here's an example of a line that you can play over these changes. The chromatics are in orange (I love orange):
The following variation of the A part became popular in the bebop era and is the version that is used the most often today:
|Bb G7b9 |Cm7 F7b9 |Dm7 G7b9 |Cm7 F7b9 |
|Fm7 Bb7b9 |Ebmaj7 Ab7#11 |Dm7 G7b9 |Cm7 F7b9 |
- The diminished chords of the previous version are changed for the chords they were substitutes for, the dominants.
- The dominants are all altered or b9
- There's more movement in the 5th bar where the V of the IV gets its II (sounds like a soap)
- The Ab7#11 in bar 6 is the tritone substitute for D7, the V of G7 in bar 7.
Here's an example voice leading for bars 5-8:
Now the B-part of the Rhythm Changes. The bridge is build out of secondary dominants (=dominant of the dominant) . The tonality is Bb major, so the primary dominant is F7, the chord in the last 2 bars of the bridge. Let's start back cycling from there: the dominant of F7 is C7, the dominant of C7 is G7 and that of G7 is D7, the first chord of the bridge. So if we sum that up, we come to this:
|D7 | |G7 | |
|C7 | |F7 | |
The obvious scales to play are:
- D7: D Mixolydian
- G7: G Mixolydian/ G altered
- C7: C Mixolydian
- F7: F Mixolydian/ F altered
In the bebop era they put the II in front of the V and we get what we call a back cycle:
|Am |D7 |Dm7 |G7 |
|Gm7 |C7 |Cm7 |F7 |
Here's an example of what you can play over this chord progression (sorry guys and girls, it seems that I am in chromatic-descending-guide-tone-lines mood):
In bar 6 I use an F minor harmonic scale.
Of course we can also use the tritone substitution for all the dominants. Then we get a chromatic bridge like this:
|D7 | |Db7 | |
|C7 | |B7 | |
And we can have more fun by adding the II:
|Am7 |D7 |Abm7 |Db7 |
|Gm7 |C7 |F#m7 |B7 |
Enjoy!
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