Secondary Dominant 7th Chords are a powerful way to expand the harmonic (and melodic) possibilities of music beyond the diatonic notes in a major or minor key…
Let’s begin by reviewing the I-V7-I chord progression in the key of C Major…
This is a such powerful chord progression because the G7 chord (V7) creates a very strong (dominant) harmonic tension, which is resolved with the return back to the C chord (I). This tension comes from three sources:
- The inherent harmonic instability of the tritone interval (B-F).
- The strong harmonic pull that the notes in the G7 chord have to resolve to notes in the C chord:
- B (Ti) wants to resolve to C (Do). This is a particularly strong attraction, so strong that B (Ti) is referred to as the leading tone, because it so strongly leads the ear back to the tonic C (Do).
- F (Fa) wants to resolve to E (Mi).
- D (Re) wants to resolve to C (Do).
- G (So) in the bass wants to resolve to C (Do).
That said, a similar tension-release formula can be used to approach any diatonic major or minor chord, not just the tonic chord. Doing so required a two-step thought process:
- Pretend that the diatonic target chord is a new tonic chord.
- Approach the target chord with the “V7” chord that corresponds to the root of the target chord. This V7 chord is called a secondary dominant 7 chord, or just secondary dominant for short.
Secondary Dominants in C Major
Let’s apply the formula above to find the Secondary Dominants in C Major…
Any of the five diatonic major or minor triads (besides the I) may be “tonicized” by approaching it with its Secondary Dominant.
These chords are Dm (ii), Em (iii), F (IV), G (V), and Am (vi).
Let’s explore the tonicization of each in order from most common to least common…
Secondary Dominant of the 4 Chord (V7/IV)
- F is the IV chord in the key of C.
- C7 is the dominant V7 chord of F.
- Functionally, C7 is the V7 of IV (V7/IV).
Hint: The appearance of Bb (Te) in a major context is an indicator that a V7/IV may be occurring.
Note: As you play each secondary dominant progression, notice the tension and sense of direction and harmonic pull that is created when the secondary dominant chord appears. In some cases, it is so strong that it can be used to create a new key center based on the tonicized chord.
Secondary Dominant of the 5 Chord G (V7/V)
- G is the V chord in the key of C.
- D7 is the dominant V7 chord of G.
- Functionally, D7 is the V7 of V (V7/V).
Hint: The appearance of F# (Fi) in a major context is an indicator that a V7/V may be occurring.
Secondary Dominant of the 2 Chord Dm (V7/ii)
- Dm is the ii chord in the key of C.
- A7 is the dominant V7 chord of Dm.
- Functionally, A7 is the V7 of ii (V7/ii).
Hint: The appearance of C# (Di) in a major context is an indicator that a V7/ii may be occurring.
Secondary Dominant of the 6 Chord Am (V7/vi)
- Am is the vi chord in the key of C.
- E7 is the dominant V7 chord of Am.
- Functionally, E7 is the V7 of vi (V7/vi).
Hint: The appearance of G# (Si) in a major context is an indicator that a V7/vi may be occurring.
Secondary Dominant of the 3 Chord Em (V7/iii)
- Em is the iii chord in the key of C.
- B7 is the dominant V7 chord of Em.
- Functionally, B7 is the V7 of iii (V7/iii).
Hint: The appearance of D# (Ri) & F# (Fi) in a major context is an indicator that a V7/iii may be occurring.
Note: With a little experience, you will start to recognize secondary dominants by sight and sound. Don’t fuss over the details right now. For the moment, it’s enough to understand the concept of extending harmony using Secondary Dominants.