One thing that has always drawn me to jazz is the harmony. It is fascinating to hear how a single chord change can define one artist's interpretation of Autumn Leaves or Night and Day from another artist's interpretation. Applied judiciously, these harmonic variations will add touches of color to your own arranging and performing.
When one chord is used as an alternate harmony for another, we call this technique chord substitution. Let's look first at the minor substitute.
Every major chord has a minor substitute that can be found three half steps below. C major's minor substitute is A minor. F major's minor substitute is D minor. G major's minor substitute is E minor.
In Example 1, the chord progression C-F-G-C becomes C-Dm7-G-C when the F major chord is substituted with Dm7.
In Example 2, the chord progression C-F-G-C becomes C-Dm7-G-Am7 when, in addition to the previous substitution, the final C major chord is substituted with an Am7.
In our third example, in addition to the two previous substitutions, the G major chord is substituted with Em7.
Another useful harmonic tool is called the tritone substitute. A dominant-seventh chord can be substituted with another dominant-seventh chord a tritone above it (six half steps). A G7 chord's tritone substitute is Db7. An A7 chord's substitute is Eb7. A D7 chord's tritone substitute is Ab7.
In Example 4, the chord progression C-A7-D7-G7 becomes C-A7-D7-Db7 when the tritone substitute (Db7) is used for the G7.
By using the A7's tritone substitute (Eb7), our progression becomes C-Eb7-D7-Db7.
Finally, with Ab7 serving as the tritone substitute for D7, our chord progression evolves into C-Eb7-Ab7-Db7.
The chord progression for "Autumn Leaves" provides a perfect opportunity to apply the tritone substitute. The first eight measures establish the harmonic pattern, one that cycles through the Circle of Fourths. Beginning with measure 9, note the tritone substitutes, each of which have been identified with an asterisk (*).
"A Simple Tune" is a musical reflection of the day on which it was written—one of the most spectacular spring days I have ever seen. Such natural beauty simply cannot be outdone, so this melody is direct and unadorned. The harmony explores both minor substitution and tritone substitution. The first two measures use major chord harmonization; the repetition of this phrase (measures 5-6) employs their minor substitutes. Measures 9-10 set up a chord progression that is mirrored in measures 13-14 with tritone substitutes.