Online Bass Instruction with Rusty Springfield
Chord Substitutions

Chord substitutions are wonderful devices, which allow one to change the "color" of a chord progression that will still blend with, and possibly even enhance, the melody of the tune. They also offer a variation of the harmony behind soloists, which can lead to new ideas and inspiration. Jazz piano players just love 'em. (Note: Listen to the recordings of Bill Evans with Scott LaFaro to hear this done by the masters.)

A very common substitution is known as the (add mysterious-sounding soundtrack here) "tritone" substitution. (Yikes !!!) Now settle down, it's not as complicated as it sounds.
There used to be a guy in the music industry whose sole job was to sit around and think of impossible sounding musical terms.

This was so music schools could charge a lot of money to decipher this stuff for the rest of us.

Apparently, it worked.
A "tritone" is the flatted fifth interval that perfectly bisects an octave. ("Then why don't they call it a bitone substitution?" you ask. See the previous paragraph.)

We've already discussed how a V7 chord tends to naturally want to resolve to it's I chord. (G7> CMaj7) Well, the tritone substitution of G7 is Db7, and it wants to resolve to CMaj7 even more than it's cousin, the G7.Think of it as a magnet. The Db7 is a half step above the CMaj7 chord, and sounds like it just has to resolve there. Try it for yourself. See? All of this works because the two dominant chords, Db7 and G7, share their 3rds and 7ths, which are the two main chord tones in a dominant chord. The third of a G7 chord is B. It's seventh is F. The third of a Db7 chord is F. It's seventh is Cb or, enharmonically speaking, B. That's why they sound so similar.

I can see the little light bulb in your head lighting up now. For those of you with halogens, notice that if the first chord is a G7(b5), it's tritone substitution is a Db7(b5). If you spell out each chord, you find that these chords are identical! I told you that this was exciting stuff!!

Another very common chord substitution involves switching a flatted third major chord or a flatted sixth major chord for a IMaj7. eg: EbMaj7 or AbMaj7 in place of CMaj7. This works particularly well if the melody note happens to be a G, since the G is the third of the Eb and the natural seventh of the AbMaj7.

Another possibility is the use of a flatted seventh major chord. eg: BbMaj7 in place of CMaj7. The G melody note would then be the 6th (or 13th) of the BbMaj7, adding more richness to the harmony. The rule of thumb is, if the melody note is found in an alternate chord structure, and the chord substitution sounds good to you, give it a try. This technique works best in a jazz context or "pop jazz" tunes such as an Al Jarreau type ballad. You could even use it to spice up an arrangement of, say, James Taylor's "Fire and Rain." I don't, however, recommend this method with "My Sharona."
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