If you’re not familiar with the circle of fifths, I strongly recommend you go here to revise it again.
A piece of music will be written in a specific key (unless it’s atonal - which means it has no key centre). This means that most of the notes will come from that key, with the addition of some melodic decorations. Sometimes to make the music more interesting or exciting a composer will change the key. This is called modulation.
The key that is used at the start of the piece is called the tonic key, or home key. In classical music the change of key is normally a temporary thing, after a while it will return home, and will usually end in the home key too. Modulating to related keys always sounds best - which is why it’s useful to know your circle of fifths inside out. More on that shortly.
How To Modulate
Pivot Chord - This is a chord that is shared with the home key and the key it is modulating to. Very often this uses the dominant chord of the home key. For example if we’re in F major, the dominant chord is C major, so we would use the chord of C to pivot into C major. This is called a V/I pivot due to the fact it is using the V of the home key and I of the key it’s modulating to.
In the example below our key is F major. We use the V/I pivot to get us into C major. Notice the B-naturals in bar six…this reinforces the new key. We then pivot on IV (which is F in C major) to bring us back to the home key.
Here’s the same piece modulating to the relative minor and back to the major home key.
There are several things you can do to modulate within a certain key - I’m using F major in this example).
Home - Relative Minor - Home
(F - Dm - F)
Home - Dominant - Home
(F - C - F)
Home - Subdominant - Home
(F - Bb - F)
You could even try
Home - Dominant - Relative Minor of Dominant - Dominant - Home
(F - C - Am - C - F)
Home - Subdominant - Relative Minor of Dominant - Subdominant - Home
(F - Bb - Gm - Bb - F)
Or if you want to be really wild
Home - Dominant - Relative Minor of SUBdominat - Relative Minor Of HOME Key - Home
(F - C - Gm - Dm - F)
Home - Subdominant - Relative Minor of Subdominant - Relative Minor of HOME Key - Home
(F - Bb - Gm - Dm - F)
Abrupt Modulation - This modulation has no pivot chord and no other preparation. It just appears from nowhere. It’s usually a semitone apart (in our example of F major it’d go to F# major ). It gives an uplifting feel or moment of excitement. Sonny & Cher’s “I Got You Babe” modulates, as does Status Quo’s version of the Fleetwood Mac song “Don’t Stop”.