Written by Gary Ewer, from “The Essential Secrets of Songwriting” website.
Changing key is a great device for injecting energy into a song. Known as modulating, it needs to be done with care, being unpleasantly startling to the listener if it’s done haphazardly. There are several ways to change key, including the “abrupt modulation,” but if you’re looking for a way to ease the song into a new key area, you will probably want to try using a “pivot chord.”
A pivot chord is one that can be understood to be in two different keys, and fulfills a different function in each. To fully understand the concept, it’s good to know about Roman numeral analysis. We identify the various chords within a key with a number, and the tradition is to use Roman numerals. Within the key of C major, the following seven chords are created by building triads (3-note chords) on each note of the major scale:
C (I) Dm (ii) Em (iii) F (IV) G (V) Am (vi) Bdim (vii)
As you can see, it’s also tradition to use uppercase Roman numerals for major chords, and lowercase numerals for minor and diminished chords.
As I mentioned, those seven chords are the ones that exist naturally within the key of C major. But those chords don’t exist exclusively in that key. For example, the chord G is the V-chord of C major, but it also exists as a I-chord in G major, a IV-chord in D major, and so on.
To change key by using a pivot chord means that we are using one particular chord, and “redefining” its function to be in a new key. Take the following progression:
This progression starts in C major, and ends up in D major. The Em is the pivot chord, because Em is the one used to change direction. In other words, we can interpret it as being the iii-chord of C major, and also as a ii-chord in D major. Here’s how the Roman numeral analysis would look:
That bent bracket in the middle of the progression is the way theorists show that a chord that was a iii-chord in the old key is going to be reinterpreted as a ii-chord in the new key.
The advantage of using a pivot chord is that it eases the ear into the new key, and gives the listener an opportunity to “adjust”. Here are some more chord progressions that move from one key to another by using pivot chords:
1. From C major to F major:
C F G C Am Bb C7 F (The Am is the pivot chord, being vi in the key of C and iii in the key of F.)
2. From C major to A major:
C F Dm G Am F E7 A (The F is the pivot chord, being IV in the key of C and bVI in the key of A.)
3. From C major to G major:
C F G C Am D D7 G (The C is the pivot chord, being I in the key of C and IV in the key of G.)
Changing key is a useful technique for creating a sense of variety in your song, and also for writing a duet, when the two singers need a melody in a different key to be singable. No matter what the circumstance, your sense of musicianship will tell you if the modulation is working or not. And keep in mind this guideline: in general, modulations upward increase song energy, while modulations downward result in diminished energy. Be careful how you do it!
Gary Ewer has written several e-books to help you improve your songwriting skills. If you’d like to discover the secrets of writing great songs, read more here.