Any chord progression can be reharmonized. Chord substitutions describe what I like to call "new harmonies with the same function." Skillful jazz guitarists of all eras make use of them in comping and improvisation.
The practice of techniques employing alternate changes allow jazz musicians to deepen their understanding of how chord progressions really work. Finding more approaches to play the same old things is invaluable.
The following article addresses the substitution of harmony on a "chord to chord" basis and then moves on to reharmonization techniques applied to entire chord progressions.
By examining one specific chord inside a progression it is possible to find alternatives. The most common way to look at this is to find chords that share common notes.
It is easy to find chords with common notes in the context of a key signature. Examine the seven chords in the "key of the moment"... and? If you pick *any* chord, two other chords in that same key will share three notes with the original! (always)
In the key of C : Cmaj7 can be substituted for Am7 or Em7.
Cmaj7 (C E G B) shares three notes with Am7 (A C E G)
(A is a third below C)
Cmaj7 (C E G B) shares three notes with Em7 (E G B D)
(E is a third above C)
And what do I mean exactly? (-;
Try this :
In the context of a band, if you play Am7 while the bassist is playing C root, it sounds like C major 6th. (Neat huh!?)
Again, in a band context, if you play Em7 while the bassist is playing C root, it sounds like C major 9th. (Even neater huh?!?!)
How is that happening? The pictured example clearly demonstrates that the notes in Em are in fact the same as Cmaj without the root :
Other chords in the key (or outside of the key for that matter) may offer interesting options for jazz guitar chord substitutions. They are yours to discover. Analyze, research, explore and make sure it sounds good to you!
Still looking at common notes, lets examine one chord type specifically : [vintage horror film tone] the terrifying "dominant 7 flat 9" chord!!!
The dom7(b9) are spelled 1 3 5 b7 b9 and are used to resolve in V-I situations most of the time. (For example : G7(b9) to C)
The beauty of the dom7(b9) is it's symmetrical characteristics (when we forget of the root.) A "B diminished 7th" chord resides inside the G7(b9)!
The dominant will get the symmetrical characteristics of it's related diminished in heritage! That's like the chord's "genetic code".
A little theory refresher :
The diminished chord being a symmetrical structure, it is movable "as is" up and down in minor thirds... Meaning that B, D, F and Ab diminished are in fact the same exact chord! (They share the same four notes.)
What does it sound like to you? Do you foresee those four possible diminished for every dominant as chord substitutions?
I say play B, D, F or Ab diminished when you see G7(b9) on the chart.
Or, more generically :
Play a diminished on the 3rd, 5th, b7th or b9th of any dom7(b9) chord.
By examining a specific progression it is possible to find alternatives. The most common way to look at this is to find progressions that share the same destination.
Caution : nothing works all of the time! Make sure you keep the chord's functionality when it's needed in the context.
Interpolation and Back Cycling :
Jazz musicians play the II-V cadence most of the time when resolving to the I chord. Therefore, the V-I can become II-V-I. It is know as interpolation. In this example, I put the II "in front" of the V :
This principle works fine even if there's no resolution to the I chord.
Simply add the appropriate II chord in front of the V, like in the "Bb rhythm changes" bridge : (each dominant is in fact a temporary "I")
So back to the situation where we want to resolve back to the I...
We had V-I becoming II-V-I. We can add another "II-V" a whole-step higher to get III-VI-II-V. And then we could even add one more "II-V" upfront. That means to start on the #IV (F#) to get to I (C) :
This is called back cycling. The added "II-V's" each contain the dominant of the next II chord. (A7 goes to Dm; B7 goes to Em and so on...)
The back cycling chords should generally be min7th(b5) to dom7(b9) because they resolve to a minor quality chord (the next II) :
Other possibilities exist of course. Here again, the other chord substitutions are yours to discover. Listen to pianists and guitarists on jazz recordings and find your own favorite back cycling tricks.
This type of substitution is the classical Neapolitan Sixth for dummies... uh, I mean for jazzmen ! Sorry (-;
Two dominant chords that are a tritone apart (three whole-steps) share the same 3rd and b7th (but "inverted" as pictured) :
The interval created by the 3rd and the b7th is a tritone. That can be a little confusing! *The tritone is a raised fourth or a diminished fifth*
Dominant chords a tritone apart share the same tritone !
The presence of this ambivalent tritone interval means that the bII chord has the same function as the V chord.
The tritone interval (present in both V and bII) tends to resolve the same way to the I chord! Try it :
That's it for the theory side of tritone chord substitutions. feeew...
Still there? Good!
In real life, tritone subs transform the "up a fourth" motion into the "descending by semi-tones" motion. Jazz musicians use this concept freely in composition, improvisation and comping.
A few good examples will clarify this. The basic III-VI-II-V-I is used to demonstrate the alternate chords :
That is just very obvious but I want to talk about it a little bit. It's like the "cherry on top" for jazz chord substitutions.
Any chord can be played using another color. It works particularly well on chords than have already been substituted. For instance, if you play Db7 instead of G7...
Try Db major 7th, or...
Db diminished 7th, or...
Db major 6th, or...
Db _________ (write your own!)
This is a great compositional and improvisational device. It creates great contrast and can give the substitution less of a "clunky" feeling.
Some examples using the same progression as above :
There is a lot more to understand in chord substitutions. I could write a book (or two) about it ... but it would be pointless to simply read about it. Real music comes from experimentation and practice. It's best to learn from recordings, in rehearsals and to attend concerts.
I established the basics on this page, you go on and find what you like how to play alternate changes. Keep your ears wide open and you'll always discover new fresh ideas.