Standards that are used for jazz often have a 32 bar sequence with an AABA form. One very common chord sequence used is that of George Gershwin’s I Got Rhythm, though usually with an original head and without the final 2 bar tag. Jazz musicians sometimes refer to this sequence as “Rhythm changes.” Along with the 12 bar blues sequence, this sequence was almost the anthem of bebop. The chord changes are of course subject to regional/stylistic variations. ex 13a shows a typical sequence based on I Got Rhythm.
This sequence shows two important variations:
(a) bars 5-6. (ex 13b-1) This variation uses chord IV minor which is altered to accommodate the passing note descending melody (or bass) line. (See Altered Chords – modal interchange).
(b) bars 13-15. (ex 13b-2) #IV diminished is used to accommodate the passing note ascending melody (or bass) line.
Both are common in Rhythm changes but would not usually appear in the same tune or at least not in the same chorus.
Some of the many variations used on this sequence:
- The middle 8 can be more complex – V7s could be converted into IIm7-V7s (see below ex 13c)
- b5 substitutes could be used. The cycle of fifths could become a cycle of semitones if alternate chords are b5 substitutes (see above tutorial 7)
- The melodic resolution to tonic at the end of each A section could fall either on bar 7 (Lester Leaps In) or on bar 8 as in the original I Got Rhythm melody.
This can have the same melodic effect as a suspended 4th on each chord – the G of the Am7 resolves to the F# of the D7.