Harmonic rhythm means how quickly do chords change.
Chords changing by semibreves would be a slow harmonic rhythm;
chords changing by quavers (at the same tempo) would be a fast harmonic rhythm.
If we increase the amount of crotchets in place of minims, we get to use more chords, and use some interesting devices:

- If you have two thirds, you can add a passing note in the middle (as in the first bar).
- If you have a repeating pattern in the melody, you can use a sequence (first bar second line)
- You can see at the end we’ve been very brave and use crotchets for each note!
Have you spotted the new chord we’ve not yet discovered? It’s hiding in bar 3…