When we part write, we have three basic ways to connect root position triads to each other.
- Root Movement by 5th
- Root Movement by 3rd
- Root Movement by 2nd
These three root movements each follow a pattern no matter what diatonic triads we connect with them: I, ii, iii, iv, V, and vi. (Remember that we are avoiding vii° in root position, as well as ii° in minor.)
Root Movement by 5th
Here are our two-chord progressions that use root movement by 5th.
- V–I (V–i)
- I–V (i–V)
- I–IV (i–iv)
- IV–I (iv–i)
- ii–V
- vi–ii
- VII–III
All of these progressions will share these properties:
- Bass sings the roots of both chords.
- One voice will hold a common tone.
- The other two voices move by step in the same direction.
We can summarize this as: 1 CT, 2 steps.
Root Movement by 3rd
Here are our two-chord progressions that use root movement by 3rd.
- I–vi (i–VI)
- vi–IV (VI–iv)
- IV–ii
- i–III
All of these progressions will share these properties:
- Bass sings the roots of both chords.
- Two voices will hold common tones.
- The other voice moves by step.
We can summarize this as: 2 CTs, 1 step.
Root Movement by 2nd
Here are our two-chord progressions that use root movement by 2nd.
- IV–V (iv–V)
- V–vi (V–VI)
- vi–V (VI–V)
- I–ii
- III–iv
- i–VII
All of these progressions will share these properties:
- Bass sings the roots of both chords.
- No common tones possible.
- Two voices move by step in contrary motion to Bass.
- One voice move by third in contrary motion to Bass.
We can summarize this as the Contary Motion Rule.
Important Note
These are the smoothest options, but they are not the only ones that work. For example, if you want V–I with Re-Do in S, you can’t write the standard root by 5th voice leading. In the standard connection, Re goes to Mi, not Do. So these smooth progressions are a guide, not a requirement.
