When I was a kid, I’d listen to music and wonder, why is this chord progression so much more satisfying than that one? Now I know the answer: secondary dominants, chords that temporarily change the key in a logical-sounding way. If you want to take your songwriting in a more sophisticated direction, you definitely want to get hip to secondary dominants.
Here’s the C major scale. The scale tones are in red, and the non-scale notes are in grey.
There’s a simple formula to use notes from C major to make a set of chords that sound good together. You start on a scale degree, and then go around the circle clockwise, skipping every other scale tone. To make a C chord, start on C, then skip over D to land on E, and then skip over F to land on G. To make a D minor chord, start on D, then skip over E to land on F, and then skip over G to land on A.
Running the formula for all seven notes in the scale gives you these seven chords, known as the diatonic chords to C major:
C: C E G (I) Dm: D F A (ii) Em: E G B (iii) F: F A C (IV) G: G B D (V) Am: A C E (vi) Bdim: B D F (vii)
The crucial chord for this discussion is G. If you add one more note to the chord, you get G7. This called the dominant chord in C, and it strongly defines the key.
The interval between the notes B and F is called a tritone, and it’s considered by western tradition to be very dissonant. When you hear the B-F tritone, your ear wants it to resolve — you want the B to go up to C, and the F to go down to E. This is the heart of the chord progression known to western music as a cadence, from Latin meaning “falling.” The G7 chord teeters unstably until it “falls” to land on the solid ground of C.
The diatonic chords sound nice, but they’re a little bland. You can spice them up by adding some more dominant seventh chords to create temporary key changes. Think of each chord in C major as the root of its own key. Each new key comes with its own dominant seventh chord, built off its own fifth scale degree. (It’s customary to ignore B diminished because it’s unstable-feeling and doesn’t work well as a root chord.) These new secondary dominants temporarily pull you out of the key of C.
Notice that all the secondary dominants are based on scale tones in C major. When you’re expecting an A minor chord and you hear A7 instead, shifting you temporarily into the key of D, it’s a recipe for deep musical gratification.
Secondary dominants in action
The most common secondary dominant in C is C7, which temporarily puts you in the key of F. I can’t even count the number of pop, rock, country, jazz, blues etc songs that use this progression:
| C | C7 | F | F |
Another very common secondary dominant in C is D7, which temporarily puts you in the key of G. You see this progression a lot, particularly in older country music:
| C | D7 | G7 | C |
The D7 includes the note F#, which is pretty dissonant in the key of C. The conflict gets quickly resolved when you hear the G7 chord, so the overall effect isn’t terribly jarring.
You’ll also hear this progression quite a bit, especially in jazz and country:
| C | A7 | D7 | G7 |
The A7 puts you in the key of D; the D7 puts you in the key of G; and the G7 lands you back home in the key of C. The A7 chord includes the note C#, which is the most dissonant note possible in the key of C. You hear that C#, and you’re like, what the heck is that? Then as the progression unwinds, it makes retrospective sense. Your brain really likes hearing this kind of conflict getting resolved.
Secondary dominants and the relative minor
The relative minor key to C major is A minor. It’s very common to switch back and forth between the two. You can do the switch using the secondary dominant to A minor, which is E7.
| C | E7 | Am | Am |
Here again, the E7 chord contains a very dissonant note, G#, which then makes perfect retrospective sense when you land on A minor.
Secondary dominants don’t have to resolve
For really advanced harmonic wizardry, use a secondary dominant and don’t complete the cadence. An especially cool usage is to fake people out with the relative minor. In the last example above, try replacing A minor with F, like so:
| C | E7 | F | F |
The F chord contains two of the same pitches as A minor, A and C. You’re surprised by the root move up to F instead of down to A, but you’re still hearing two of the notes you were expecting. Hip! Two of my favorite songs from very different eras use this device. One is “Freight Train” by Elizabeth Cotten; the other is “Empire State of Mind” by Alicia Keys and Jay-Z. The fakeout progression happens going into the chorus.
Another popular secondary dominant fakeout is to use D7 without resolving to G. Plenty of folk, rock and country songs will just go straight from D7 back to C. Neil Young is especially fond of this maneuver, for example at the end of each verse of “Harvest.” Bob Dylan uses it too, in “Don’t Think Twice, It’s Alright.”
Around the circle of fifths
Check out what happens when you arrange the secondary dominants around the circle of fifths. You can start on any of them and work your way around the circle counterclockwise to make chains of cadences.
Going around the circle of fifths using dominant chords is a time-honored songwriting technique, and a sound you’ll instantly recognize from jazz, ragtime and Tin Pan Alley songs. The best example is the bridge of “I Got Rhythm” and the uncountable jazz tunes based on it. Usually it’s played in B flat, but for consistency, here it is in C:
| E7 | E7 | A7 | A7 | D7 | D7 | G7 | G7 |
Use a dominant to get to any key
Any time you want to jump to a new key, you can get there via its dominant chord. Want to jump to Ab? Get there via Eb7. Want to jump to F#? Get there via C#7. It isn’t the only way to introduce a new key, but it is the smoothest. Using cadences gives your tunes a feeling of structure and logic, and lets you introduce all kinds of exotic dissonances without alienating your listeners.