Many incredible songwriters (Elton John, The Beatles, David Bowie, Louis Armstrong, Bob Dylan, and many more) are proficient in how secondary dominant chords can add soul and sophistication to an otherwise ordinary diatonic chord progression. Secondary dominants allow songwriters to modulate to a new key (just briefly for the secondary dominant chord itself, or for a whole section of a song i.e. bridge), and also modulate flawlessly back to the original key. Think of secondary dominants as a magical wormhole to and from another closely related key.
In order to learn how secondary dominant chords function in songs, there are three concepts we’ll need to understand first:
Concept 1 – Diatonic structure: This is the structure of chords in every major key. It is usually written out using roman numerals (upper case for major, lower case for minor/diminished) like this: I, ii, iii, IV, V, vi, vii . These chords are naturally occurring within the major scale key. Because of this, all major keys have the exact same structure of chords within them. Roman numerals make it easier to theoretically analyze and communicate details about these chord structures. For example, a I, IV, V chord progression will generally sound the same in every key, however, some keys may sound higher and lower than others.
We can take this concept a step further by looking at the diatonic structure of seventh chords, which looks like this in the key of A:
(Roman Numeral = Chord Type = Actual Chord)
I = Maj7 = AMaj7
ii = min7 = Bmin7
iii = min7 = C#min7
IV = Maj7 = DMaj7
V = 7 (dominant 7) = E7
vi = min7 = F#min7
vii = dim7 / min7 b5 = G#dim7
Concept 2 – Dominant exclusivity: Take a close look at the entire diatonic structure of seventh chords listed above. Notice how there is only one dominant seventh chord in the list (it’s E7 – everything else is minor seventh, major seventh, or diminished*). Because there is only one dominant seventh chord in the diatonic structure, there is only one dominant seventh chord in any given major key. Because of this, any song with 2 or more dominant chords within it is guaranteed to be in more than one key.
Blues is a very good example of this; relatively simple chords (A7, D7, E7), repeating in a simple form (12 bar blues), yet Blues never seems to get old to the listener. Sure, powerful lyrics and soloing help fill in the structure of the blues, but ultimately there is magic in the chords themselves because every time you change chords in a blues you are also changing the key! This keeps things interesting to the listener, but makes Blues much harder to understand in theory. Many teachers avoid this altogether, and rather put more emphasis on the “just feel it” aspect of the blues, which is also extremely important. I think its important to first light the path and really see what’s going on before we “just feel it”.
Here’s the breakdown of the three keys that create a Blues in “A”:
A7 = key of D Major
D7 = key of G Major
E7 = key of A Major
*Keep in mind a dominant seventh chord is different from a major seventh chord, or a minor seventh chord. It is a major triad with a flat seventh added. It sounds very bluesy, and kind of unsettled, it usually wants to move to another chord.
Concept 3 – Dominant seventh chords are V7 chords: V7 chords always resolve nicely to a I chord. E7 doesn’t only resolve to A major, it resolves to any chord built of the note A! A major is the most common resolution from E7, but A minor also has a wonderful charm to it as well (fur eloise, house of the rising sun, ect). Because a V7 chord will resolve to either a major or a minor chord, secondary dominants can be chosen to resolve to any diatonic chord in a key, except the I chord (The I chord already has a V7 chord and its in the key. I also omit the secondary dominant off the vii chord as it just doesn’t sound right to my ear). The secondary dominant chord is always 5 notes higher than the diatonic chord it is built off of, because it is technically a V7 chord that was borrowed from another key. With this in mind, there are five secondary dominant chords that can resolve back into the key of A, and they are:
I = no secondary dominant
V7/ii = F#7 / Bmin7
V7/iii = G#7 / C#min7
V7/IV = A7 / Dmaj7
V7/V = B7 / E7
V7/vi = C#7 / F#min7
vii = dim7 = no secondary dominant
As far as pronunciation of secondary dominants, use the word “of” in place of the / symbol. For example, V/ii is pronounced “five of two”.
The idea here is to supplement a diatonic chord progression (in this case in the key of A) by adding in one or more of these secondary dominant chords. Many songs only use one of these secondary dominants, as these chords can have quite a powerful effect. A great example of this is the song Good Lovin’ by The Rascals (there’s also a fantastic cover version played by the Grateful Dead). The chords of the verse and chorus is simply D, G, A, G, or I, IV, V, IV in D Major. Right before the chorus during the “Yes Indeed … All I really Need” part, they play an E7 going into A7. Since the original key of the song is D Major, the E7 is a V7/V in D Major, and that leads us back into the A7 which is the V7 in D major. There’s a short break and its back into the D, G, A, G, or I, IV, V, IV in D Major. That’s it, just one bar of secondary dominant chord. A little secondary dominant can go a long way, in this case it really brings the energy up quite a bit, plus it’s very hard to imagine this song without it.
You can also use the secondary dominant chord to modulate into a totally new key. For this example lets bring it back into the key of A major. We could use a B7 (V7/V) to temporarily modulate to the key of E major (B7 is the V7 in E major). This approach could be great for composing a bridge of a song, as we’re always trying to make the bridge sound different, and pop out from the rest of the song. Modulating the entire bridge section into a new key is a fantastic way to achieve this.
One of the most beautiful things about secondary dominants is they give you a path to a new key, as well as a path back to the original key. In other words, the B7 (V7/V) brings you into the key of E for how ever long you’d like. Some songs may just use the B7, then immediately modulate back to the original key (like Good Lovin’). Other songs may stay in the key of E a bit longer, then modulate back to the original key after that section is over.
The simplest trick for modulating back to the original key is to follow the secondary dominant path, then re-establish the original key.
In this example, the actual chords are listed on the left (AMaj), the current key of the song is in the middle (A:), and the roman numerals and theoretical break down is listed on the right (I) :
AMaj – A: I
C#min – A: iii
DMaj – A: IV
AMaj – A: I
B7 – A: V7/V
(Secondary dominant allows modulation into key of E)
EMaj – E: I
G#Min – E: iii
AMaj – E: IV
EMaj – E: I
Secondary dominant (to lead back into the original key of A)
B7 – A: V7/V
Establishing the original key (with a V7 to I)
E7 – A: V7
AMaj A:I
This may not be the worlds most interesting chord progression, but I think it demonstrates how we can start a song in the key of A, then use a secondary dominant to modulate briefly into the new key of E major, then use the secondary dominant again to modulate back into the key of A major. This process gets easier the more you work with it, and there’s no hard set rules here, think of these as suggestions to get you from one place to another, in practice we may simplify, or skip chords so long as it sounds good to the ear.
Here’s a few great examples of songs and artists that use secondary dominants:
Starman – David Bowie
Blackbird – The Beatles
What a Wonderful World – Louis Armstrong
Yesterday – Paul McCartney
Most Songs – Elton John
Eternal Flame – The Bangles
The Longest Time – Billy Joel … and like every other Billy Joel song as well.
Don’t think Twice, It’s Alright – Bob Dylan
Dancing Queen – ABBA
Drew Krag Music 