Secondary Dominant ③ / Music Theory Lesson

Dominant of a Dominant Chord

Previously we took a look at the “V→I” resolution, and applying them to other major diatonic chords to create secondary dominant chords.
The chords leading to the 5th and 7th diatonic chords sounded particularly unstable, and we will be taking a look at the reason for this.

Lets examine this in the key of C major.
Though we had mentioned that the chord leading to the 7th can be considered a secondary dominant, because resolving to a m7b5/dim chord as a I is too unstable, generally a VIIdim/VIIm7b5 does not have a secondary dominant chord.
Lets give this concept a listen.

F#7→Bm7b5

F#→Bdim

F#7→Bdim

V7/V

Lets check the chord leading to the 5th as well.

D7→G7

D→G

D7→G

When we went to the G chord there was a sense of resolution, but you may have felt an unnaturalness when going to the G7 if you are not familiar with blues style sounds.

Lets give this another listen:
D7→G7

This progression moves from the II7 to it’s tonic V7, a dominant diatonic chord.
This means that it is the secondary dominant chord of the dominant chord in the key, yet similar to a II V dominant to tonic motion
Because of this, it’s function and purpose works slightly differently.
This time, we will be looking at this concept in detail.

About a Dominant of a Dominant Chord

There is a special name for the 5th chord in the diatonic chord scheme in Japan.

You may hear it being called the
double dominant or dopple dominant.

The secondary dominant chord allowed us to modulate momentarily and resolve to a chord that followed.

For example, we may modulate for a moment to the key of F major.

V7/IV

C7→Fmaj7

C→F

C7→F

Lets change the voicings and see this again.

This II７(V7/V)→Ⅴ７ progression has a tritone in the II7 that move simultaneously down a half step, to connect to the V7 tritone.
Because both are dominant 7th chords when 7th notes are played for both, they both contain tritone intervals as well.

Though the example above is just the dominant to dominant movement in the key of C, we will continue this dominant to tonic motion using this same progression.

By doing so, we get the following chords:
D7→G7→C7→F7→Bb7→Eb7→Ab7→C#7→F#７→B7→E7→A7→ back to D7→G7→…

You may have felt like you’ve seen this order of letter somewhere before.

Yes, it is the order of the circle of 5ths.
You can think of it as each key’s dominant chord being displayed as well.

By using the system above, you can transfer into various different keys and eventually stabilise with a different chord.
Lets try it out.

Though the original key is C…

Chords
C→Am→Dm7→G7→C7→F7→Bb7→Eb

We have landed safely in Eb major.

Of course, using the knowledge on harmonic/melody minor we can

Chords
C→Am→Dm7→G7→C7→F7→Bb7→Ebm

land safely in Eb minor as well.

Next time, we will look at using our prior knowledge on these topics in real world situations and chord progressions.