Understanding the secondary dominant is essential to understanding how most jazz tunes work harmonically as well as understanding how to choose the proper scale with which to successfully improvise melodically. The concept itself is straight forward. Since we know that the dominant to tonic progression is essential to establishing key areas in tonal music it is just a matter of extending the relationship to other chords within the key. The effect is to temporarily shift the tonal center from tonic to some other key area usually related to the home key. For example in the key of C major we might want to temporarily move into G major or A minor or any other related key for variety. The closely related key areas correspond to the diatonic triads derived from the scale. In the key of C major the related keys would be D minor, E minor, F Major, G Major and A minor. We know that G7 is the dominant seventh chord in the key and has a strong pull back to tonic (C). All we have to do to create a secondary dominant is figure out what is the dominant seventh chord of any other chord in the key and precede that chord with its dominant. This will become clearer as we look at some examples.
As we discussed earlier, chord progression based on root movements through descending fifths are frequently used in tonal music and are very common in jazz. This type of progression lends itself well to the use of secondary dominants. Let’s take a look at the ii-V-I progression (roots descending by fifth) as an example of how we can use a secondary dominant. The chords are Dm7 G7 CMaj7 in C. We know G7 is the dominant. What is the dominant of G? The answer is D7. Since D is a perfect fifth above G the D7 chord is the dominant of G. This relationship is known as V of V since G is V in C major and D7 is the V of the V. So we can change the Dm7 chord to a D7 chord in this progression to temporarily move us into the key of G major only to return to C major immediately after with the G7 chord. Let’s expand this again and figure out what is the V of D? The answer is A7 for the same reason as above. So we can precede the D7 with an A7 chord again moving us briefly into D minor or the area of the ii chord (supertonic). Remember that D7 cannot be a tonic chord because of its instability so the key we are moving into is D minor. So if for instance we have the basic vi-ii-V-I progression (Am7 Dm7 G7 CMaj7) this could now become A7 D7 G7 CMaj7 utilizing two secondary dominants. We would refer to the A7 chord as V of ii. Try playing the basic diatonic progression and then use the secondary dominants and listen for the interesting new colors that are introduced.
As a rule jazz tunes usually use this concept to enhance a basic progression and make it much more interesting to solo over. A good example is the turn-around progression (iii-vi-ii-V-I) or Em7 Am7 Dm7 G7 CMaj7. In actual practice the Am7 chord is usually altered to an A7 chord creating a secondary dominant of the ii chord Dm7. The new progression then would be Em7 A7 Dm7 G7 CMaj7 which is much more fun to solo over since every other chord is now a different quality. Another excellent example of secondary dominant usage would be the bridge section of “rhythm changes”. Take a look at “Oleo” for example. The bridge changes are D7 G7 C7 F7 which is the iii-vi-ii-V progression in Bb altered to create secondary dominant relationships.
To summarize, we can precede any chord, with the exception of m7b5 and diminished seventh chords since these are never tonics, with dominant seventh chords a perfect fifth above. If the chords are already in perfect fifth relationships we can change or alter these chords from their diatonic state to dominant sevenths creating secondary dominant relationships. This combined with the tritone substitution (see earlier article) gives us very powerful tools for enhancing basic chord progressions.
It is important to note that I have shown the dominant seventh chords in the most basic way. Jazz musicians understand that although the chord is written as a basic seventh chord it is almost never played as written. The dominant seventh chord should always be embellished by adding the 9th, 11th and 13th extensions (any or all) and any or all of the four possible altered tones: b9, #9, b5 and #5. Without these embellishments and alterations your chord changes will sound anemic. There are some fundamental rules for using these embellishments which I will discuss in the future. For now let your ear guide you; it is usually right.
Please see these musical examples for further explanation: