Some songs sound like the world suddenly widened at the chorus. Usually the key moved. Modulation looks intimidating, but moving to a nearby key is mechanically simple.
Everything so far has stayed in one key. You can also move the key itself part-way through a song. That is modulation.
Near keys and far keys
Keys next to each other on the circle share six of their notes, so moving between them barely registers as strange. Keys on the opposite side share few notes, so moving there is jarring — or striking, depending on what you want.
C, G, F and Am all sound like relatives, because they hold most notes in common. When modulating, picking a close relative first is the safe route.
Moving to a different key part-way through a piece. Nearby keys feel natural; distant ones feel dramatic.
Place one bridging chord
To move from C to F, put C7 just before the arrival. C7 contains B♭, a note belonging to F, so it walks the listener's ear into the new key. It is the pulling mechanism from chapter 16, used to move the key instead.
- Stays in C (C, Am, F, G)
C | Am | F | G
- Through C7 into F (C, Am, C7, F)
C | Am | C7 | F
In the second one the final F sounds like the home chord of a new key rather than the IV of the old one. Same F chord — what comes before it changes its job.
- Chords do one of three jobs: home, opening out, tension.
- The standard progressions are rotations of a few chords, and are not copyrightable.
- The royal road ends aching; the Komuro progression ends bright.
- Cadences create the sense of an ending, and should differ by section.
- One borrowed note strengthens the pull — and the same trick modulates.
That closes part three. Part four is about how a melody moves over these foundations. Before that, write something over a progression that modulates.
Generate over C, Am, C7, FNeighbouring keys share notes, so moving between them feels natural. The basic move is one bridging chord.