Have you ever looked through or played a piece of music and noticed that you have been playing a few dominant 7th chords which are not part of the key of the piece?
Take a look at this example, Billy Joel’s “New York State of Mind”:
And take a listen:
By now, you should already know that each scale, whether major or minor, produces a dominant 7th chord on the 5th degree of the scale. (Special instances are the natural minor which has its dominant 7th chord on the 7th degree and the melodic minor which has an additional dominant 7th on the 4th degree of the scale. Please review diatonic chords of minor scales here.)
Let’s focus on the ones that are built on the 5th degree of the scale. This V7 chord is also called the primary dominant, i.e. the main and only dominant 7th that is created naturally on the 5th note of the scale, be it major, harmonic or melodic minor.
In the Key of C Major:
Notice the strong root movement that is produced by the V7 chord moving to the tonic — i.e. either a perfect 5th down or perfect 4th up, which also brings to mind the ever-important Cycle of 5ths movement.
In contemporary music, a secondary dominant is a dominant 7th (or occasionally the triad version, especially in pop songs) that moves either a perfect 5th down or perfect 4th up to any other chord in the scale/key other than the tonic or first chord. That means we can have a V7 chord quality moving into chord IImi, IIImi, IV, V, and VImi.
Here are the seven diatonic chords in the Key of C Major, followed by secondary dominants preceding each available diatonic chord in the key:
The use of secondary dominants in a song provides added chromaticism or color to the existing chords. This is because each secondary dominant chord contains at least one chromatic note (a note that is outside the key or scale of the song). This chromatic note can be the 3rd, 5th and/or b7th of the dominant 7th chord. [The secondary dominant of IIImi contains two chromatic notes.] Notice also that all the roots or bass notes of these secondary dominant chords are all diatonic (belonging to the scale) to the key. This help make the chords “rooted” to the home or tonic key since each chord itself will already contain at least one note that is outside of the scale.
In “New York State of Mind” which also happens to be in the key of C major, G7 is the primary dominant chord, V7. The other dominant 7th chords — D7, E7#9 and C7 — are secondary dominants of G (V) , Ami7 (VImi7) and F (IV), respectively, and you can clearly see how each chord moves in the Cycle of 5ths in the chord progressions, i.e. D7 to G; E7#9 to Ami7; and C7 to F.
The seventh degree of the scale being a minor 7th flat five chord (and therefore a “weaker” sounding chord) traditionally does not have a secondary dominant moving into it. Notice also that if a dominant would to be applied to this min7b5 chord, the root or bass of the chord would be chromatic to the key, i.e. in the above example of Key of C major, the dominant 7th of Bmi7b5 would have to be F#7. This goes against one of the the principles behind using the secondary dominant.
Now that you know how useful the application of these chords can be, I’m sure you’d like a “second-ary V7” helping! 🙂
[All music and video clips used for educational purposes only.]