How to Improvise Over Substitute Dominant Chords | Hub Guitar

How to Improvise Over Substitute Dominant Chords

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Substitute dominant chords are dominant 7th chords which resolve down by half-step. They work by imitating the dominant chord that would normally resolve to the target. For instance, the dominant chord for a Cmaj7 is G7, which has G, B, D and F. The key element of this chord is the B and F, which is a dissonant "tritone" interval. If we play a Db7, that chord has Db, F, Ab, Cb (B), which means it has the same tritone so it will work as a dominant resolution.

Let's look at a basic chord progression: III-7, VI-7, II-7, V7 and I E-7, A-7, Dm-7, G7 and Cmaj7

Now I'll turn the VI-7 to a sub V of II, Eb7. And I'll take the V7 and convert it to a subV of I, Db7. These chords are often played with a flat 5, as more often than not the natural five is out of the key, making the chord sound more tense, but the flat five is actually in the key, making the chord fit a bit better.

E-7, Eb7b5, Dm7, Db7b5, Cmaj7

How would we improvise over that?

The first way is to just change whatever notes of the key were changed by the new tones in the chord.

For Eb7b5 we have Eb, G, A, Db. So we would change all E to Eb and all D to Db.

For the Db7b5, we have Db, F, G, B. So just change the D to Db.

I'm not going to demonstrate that example because it can produce unpredictable results as we're assuming that the rest of the C major notes will work on the chord as long as there is no conflict with a chord tone and that can produce some unusual results, although you can try it yourself--but that is one of the most fundamental ways to learn to improvise on different chords.

The next thing we can do is play a chord scale associated with that dominant 7 flat 5 sound. That would normally be a Lydian b7, which is like a mixolydian scale for a dominant chord, but with sharp 11, which is basically the same as b5.

For something even more straight forward, just grab a chord tone of the substitute dominant chord and play a whole tone scale. That works fairly well and it's pretty approachable. That's the approach I'm gonna use in the demonstration. So to get start with that idea, try playing that whole tone scale to deal with improvising over these chords and later on you'll try Lydian flat 7 as well.


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 7th 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 4th 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 ♭7123♯456♭7
Whole Tone123♯11♯5 ♭7

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

FunctionChords4♯11P5♯5
sub V/ID♭7G♭GA♭A
sub V/IIE♭7A♭ AB♭B
sub V/IIIF7B♭BCC♯
sub V/IVG♭7C♭CD♭D
sub V/VIB♭7E♭EFF♯

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-7VI-7II-7V7Imaj7
E-7A-7D-7G7Cmaj7

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

III-7sub V/IIII-7sub V/IImaj7
E-7E♭7D-7D♭7Cmaj7

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

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.

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