Ultimate Guitar Lesson

XII. Non-Diatonic Chords

Secondary Dominants.

Life was too easy when a key center had only one dominant chord.
C Major:

CMaj7 Am7 Dm7 G7
Imaj7 vim7 iim7 V7

Secondary dominant chords increase the feeling of tension and therefore add interest. Here’s the same progression with secondary dominants.

CMaj7 A7 D7 G7
Imaj7 V7/ii V7/V V7

* The overall key center does not change with the addition of these chords.
* Major triads may be used instead of complete dominant chords.
* A secondary dominant chord may be left unresolved.

CMaj7 A7 F G7
Imaj7 V7/ii IV V7

Major Key Secondary Dominants
This is the complete list.

V7/IV V7/V V7/vi V7/ii V7/iii

* There is no V7/vii.
* IV7 occurs but it is not considered a secondary dominant.

Minor Key Secondary Dominants

I7 II7 bIII7 IV7
V7/iv V7/v V7/bVI V7/bVII

Write out the possible secondary dominants in various major and minor keys.

Modal Interchange
In a major key progression, chords may be borrowed from the parallel minor key.
Here are the chords in A major and in its parallel minor, A minor.

A Bm C#m D E F#m G#dim
Am Bm7b5 C Dm Em F G

Here is a chord progression interchanging the two, with the borrowed chords highlighted.

A Major
A F#m D F G A Dm
I vi IV bVI bVII I < >ivm

In a minor-key progression, chords may be borrowed from the parallel major.

Am F D G A C

Write the keys and chord functions and qualities, and label instances of secondary dominants and modal interchange on Beatles songs or other pop music.

Flat-Five Substitution
This is also called tritone substitution. A dominant chord may be replaced by a dominant chord a b5th away from its root.

Em7 A7 Dmaj7
iim7 V7 Imaj7
After b5 substitution this becomes:
Em7 Eb7 Dmaj7
iim7 bII7 Imaj7
The substitute chord can be named by its actual position as shown above, or by what it subs for, shown below.
Em7 Eb7 Dmaj7
iim7 bV7/V Imaj7
Flat-five subs can also replace secondary dominants.
E G#m7 C#7 F#7 B7 EMaj7
E G#m7 G7 C7 B7 EMaj7
I iiim7 bV/vi bV/ii V7 Imaj7