Chord Substitution - Application

Application

In jazz, chord substitutions can be applied by composers, arrangers, or performers. Composers may use chord substitutions when they are basing a new jazz tune on an existing chord progression from an old jazz standard or a song from a musical; arrangers for a big band or jazz orchestra may use chord substitutions in their arrangement of a tune, to add harmonic interest or give a different "feel" to a song; and instrumentalists may use chord substitutions in their performance of a song.

Jazz "comping" instruments (piano, guitar, organ, vibes) often use chord substitution to add harmonic interest to a jazz tune with slow harmonic change. For example, the jazz standard chord progression of "rhythm changes" uses a simple eight bar chord progression in the bridge with the chords III7, VI7, II7, V7; in the key of B♭, these chords are D7, G7, C7, and F7 (each for two bars). A jazz guitarist might add a "ii-V7" aspect to each chord, which would make the progression: "a minor, D7, d minor, G7, g minor, C7, c minor, F7. Alternatively, tritone substitutions could be applied to the progression.

Note that both the back door progression and ♯IIo7, when substituted for V7, introduces notes that seem wrong or anachronistic to the V7 chord (such as the fourth and the major seventh). They work only because the given instances of those chords are familiar to the ear; hence when an improviser uses them against the V7, the listener's ear hears the given precedents for the event, instead of the conflict with the V7. —Coker (1997), p.82

Theoretically, any chord can substitute for any other chord, as long as the new chord supports the melody. In practice, though, only a few options sound musically and stylistically appropriate to a given melody. This technique is used in music such as bebop or fusion to provide more sophisticated harmony, or to create a new-sounding re-harmonization of an old jazz standard.

Jazz soloists and improvisers also use chord substitutions to help them add interest to their improvised solos. Jazz soloing instruments that can play chords, such as jazz guitar, piano, and organ players may use substitute chords to develop a chord solo over an existing jazz tune with slow-moving harmonies. Also, jazz improvisers may use chord substitution as a mental framework to help them create more interesting-sounding solos. For example, a saxophonist playing an improvised solo over the basic "rhythm changes" bridge (in B♭, this is "D7, G7, C7, and F7", each for two bars) might think of a more complex progression that uses substitute chords (e.g., "a minor, D7, d minor, G7, g minor, C7, c minor, F7). In doing so, this implies the substitute chords over the original progression, which adds interest for listeners.