We will now add two predominant chords to our arsenal: IV (iv) and ii (ii°).

Subdominant

IV as a Predominant

IV will function as a predominant chord when it goes to V. The most common version of this progression is I–IV–V–I(i–iv–V–I). Make sure you apply the Contrary Motion Rule when part writing IV–V.

I–IV–V–I (i–iv–V–i)

• Bass: Do-Fa-Sol-Do
• Upper voices, each a possible melody in the S.
  • Mi-Fa-Re-Mi (Me-Fa-Re-Me)
  • Sol-La-Sol-Sol
  • Do-Do-Ti-Do

There is one other part writing possiblity for IV–V: writing La-Ti-Do in the S.

• Bass: Fa-Sol-Do
• Soprano: La-Ti-Do
• Inside voices
  • Fa-Re-Mi
  • Do-Sol-Sol

IV as a Tonic Prolongation

IV can also occur between two tonic chords: I–IV–I. By returning to I after the IV, we are still in the tonic function, still waiting to move onto the predominant or dominant functions. Theorists call this function of IV a tonic prolongation. You can think of IV here as elaborating the tonic chords surrounding it. Make sure you follow the part writing.

I–IV–I (i–iv–i)

• Bass: Do-Fa-Do
• Upper voices, each a possible melody in the S.
  • Mi-Fa-Mi (Me-Fa-Me)
  • Sol-La-Sol
  • Do-Do-Do

Plagal Cadence

IV–I: See Classical Cadences.

Supertonic

ii will only function as a predominant chord in the style we are emulating: ii–V (ii°–V). This chord is very strong as a predominant, because of its root movement by 5th going to V. The chord progression ii–V–I is also very common in jazz music.

I–ii–V–I

• Bass: Do-Re-Sol-Do
• Upper voices, each a possible melody in the S.
  • Mi-Re-Re-Mi
  • Sol-Fa-Sol-Sol
  • Do-La-Ti-Do

IV and ii Together

It is possible to have both predominant chords happen together in music. IV will go to ii, and not the other way in the style we are emulating. Note IV–ii is a root movement by 3rd.

IV–ii–V–I

• Bass: Do-Fa-Re-Sol-Do
• Upper voices, each a possible melody in the S.
  • Mi-Fa-Fa-Sol-Sol
  • Sol-La-La-Ti-Do
  • Do-Do-Re-Re-Mi

Note that it is possible to use any version of V–I listed on Part Writing Tonic and Dominant in all these progressions.

ii in First Inversion

The supertonic is most common in classical style in first inversion: ii⁶ (ii°⁶). I–ii⁶–V–I mixes the very strong bass line Do-Fa-Sol-Do from I–IV–V–I with the minor ii chord. Diminished triads are often avoided in root position because of their instability, so make sure you write ii°⁶ in minor keys rather than ii°. See First Inversion Triads.