How to Improvise Over Substitute Dominant Chords

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Choosing a Scale to Play for Substitute Dominant

First of all, would you recognize a substitute dominant chord if you saw one?

We've got a whole lesson on understanding substitute dominant chords in case you're a bit unclear on what those are.

A substitute dominant usually has these features:

It is normally a dominant 7^th chord, though a major triad can sometimes imply it
It is a chord that is outside of the key
It resolves down by half step, as in from D♭⁷ to C
It often has a ♭5 (or a ♯11, which can imply ♭5)

Why is the Fifth Flat?

The substitute dominant chord is often played as a dominant 7 flat 5. Since the root of the chord is out of the key, the perfect fifth is also likely out of the key, too. If you think about that, flattening the fifth can have a more consonant result with the original key. This fulfills the function of the chord without adding unnecessary chromaticism.

Basic Method of Improvisation

We can use the "basic method" of improvising over the substitute dominant, by altering the notes of the key which are different when the chord is compared to the key. This is one of the easiest ways to do it.

For instance, in the key of C major, using D♭⁷ as the sub-V/I, the notes of the chord are D♭—F—A♭—C♭.

Since C♭ is "really" B, we just have to adjust the D's and A's of the scale to be D♭'s and A♭'s. That would leave us with an Ionian scale, ♭2, ♭6. Let's not even bother putting a name on that.

A Second Improvisation Method – Lydian ♭7

The lydian ♭7 scale is commonly used to improvise over substitute dominant chords. This scale begins perhaps as a Mixolydian scale, the most basic scale for improvising over dominant chords. The 4^th is altered to allow for the likely appearance of the ♯11 in the melody.

An Even Easier Method – Whole Tone Scale

The Lydian ♭7 scale and the whole tone scale differ by only one note.

Comparing Lydian ♭7 to Whole Tone Scale

Lydian ♭7	1	2	3	♯4	5	6	♭7	Listen: ex_lydian-b7
Whole Tone	1	2	3	♯11	♯5		♭7	Listen: ex_whole-tone

As you can see, both scales enjoy the basic augmented sound in the first four notes. And both have a ♭7. They differ only in terms of degrees 5 and 6. In many cases, it might be better to have a ♯5 than a natural 5, as you'll see below. And in these cases, the whole tone scale might be a better choice.

Substitute Dominants in C

Function	Chord	s4	♯11	P5	♯5
sub V/I	D♭⁷	G♭	G	A♭	A
sub V/II	E♭⁷	A♭	A	B♭	B
sub V/III	F⁷	B♭	B	C	C♯
sub V/IV	G♭⁷	C♭	C	D♭	D
sub V/VI	B♭⁷	E♭	E	F	F♯

The chord tones that fit in the original key are highlighted. As you can see, in many cases, ♯11 and ♯5 on a substitute dominant are more likely to be a part of the original key than ♮4 and ♮5. So it's really not that crazy to use Lydian ♭7. And in any case, ♯11 always fits the key! No wonder it's so common.

So the whole-tone scale is a bit more "in" for V/I, V/II, V/IV. For V/III and V/VI, Lydian ♭7 fits the key a bit more. But you can use either scale in any case.

Improvisation Exercise for Substitute Dominants

The backing track below has a chord progression that begins as a diatonic one, but then turns into a substitute dominant progression.

III^-7	VI^-7	II^-7	V⁷	I^maj7	%
E^-7	A^-7	D^-7	G⁷	C^maj7	%

After the first time through, the second and fourth chords become substitute dominant chords instead, creating a chromatic bassline:

III^-7	sub V/II	II^-7	sub V/I	I^maj7	%
E^-7	E♭⁷	D^-7	D♭⁷	C^maj7	%

These two progressions will repeat several times.

Practice playing the chord progression and the bassline. Can you write an ostinato (simple, repeated melody over all chords?)

According to our little theory above whole tone scale matches both chords pretty well. (And has the advantage of being pretty easy to play!) So try improvising over the tune with the whole tone scale.

Backing Track: Substitute Dominants

Listen:

gm-backing_track_19

Key Result

After mastering this lesson, you can:

Recognize the sound of a chord that acts as a substitute dominant.
React by playing, at minimum, a whole tone scale—allowing you to keep your improvisation notes consistent with the chord.