Did you ever noticed, when playing in a band or with backing track, that some of traditional chord substitutions do not sound well over original changes? There are reasonable answers why it is so, and what could be done to avoid such irritating effect, without limiting (and even expanding) palette of handy harmonic devices.
At first, let us define what traditional chord substitutions are. They are harmonic devices for creative reconstruction of already known chord changes, without doing any damage to their functional features. Chord substitutions developed gradually, as more and more sophisticated and modern recipes of harmonic variation.
We all know at least few of those:
Diatonic substitutions (Em7 instead of Cmaj7)
Secondary dominants (C C7 | F G7)
Secondary II V`s (C Gm7 C7 | F G7)
Tritone substitutions (Db7 instead of G7, or Abm instead of Dm)
Sudden change of chord type (Ebmaj7 instead of Eb7 – tritone sub for Am7 or A7)
Passing chords (C C#dim7 | Dm G7)
Coltrane substitutions (Dm7 Eb7 | Abmaj7 B7 | Emaj7 G7 | Cmaj7 instead of Dm7 | G7 | Cmaj7 | Cmaj7)
Root movement by minor third (Bb7 instead of G7 or Db7)
Backcycling (E7 A7 | D7 G7 | C7 | C7 instead of G7 | G7 | C7 | C7)
Side-slipping (Ebm7 Ab7 | Dm7 G7 instead of Dm7 | G7)
Chromatic approach chords (C Bb7 | Am C#m | Dm Ab7 | G7 B7 instead of C | Am | Dm | G7)
You name it…
When using as melodic (arpeggio) devices, chord substitutions could work really well, if played in fast and convincing phrases. Predictably structured series of notes become relatively independent of harmonic context until the point of resolution. They are self content to the listeners` ear, because of very dynamic nature.
Audible conflict between original changes and substitutes occurs in slower tempo, when trying to accent or lean on notes of substitute arpeggio, also in chordal improvisation. It happens because some of chord substitutions have been created foremost as compositional devices and are not really suitable for vertical improvisation, because of avoid tones and chromaticisms (vertically unstable notes) they contain. Riddle of vertically stable and unstable substitutions emerged historically and I will propose clear technical solution for it in progress of series of following articles.
Once more: we could alter original chord changes using any of traditional chord substitutions and still retain the same functional logic, but we could not always do that during spontaneous jam session – original changes and their substitutions sometimes may not sound well, played simultaneously.
Let us analyse and hear few examples, when original chord and common traditional substitute misfit:
G7 (V7) ≠ Abm7 (tritone substitution of Dm7 (IIm7), quite common before Db7 (bII7) instead of G7).
Notes of G7: G B D F, it is 1 3 5 b7.
Notes of Abm7: Ab Cb(B) Eb Gb(F#), it is b2, 3, b6, 7, according to G7.
Both summarized: 1, b2, 3, 5, b6, b7, 7. b2 and b6 are avoid tones, b7 and 7 – arpeggio conflict.
Am7 (VIm7) ≠ Ebmaj7 (tritone substitution of VIm7, chord type changed, as in common cadence Cmaj7 Ebmaj7 | Abmaj7 Dbmaj7)
Notes of Am7: A C E G, it is 1 b3 5 b7.
Notes of Ebmaj7: Eb G Bb D, it is b5 b7 b2 4, according to Am7.
Both summarized: 1 b2 b3 4 b5 5 b7. b2 is avoid tone, b5 and 5 – arpeggio conflict.
If these examples did hurt your ears (sorry for that), you are ripe for further studies, which will follow here shortly.