First inversion triads are where the creativity comes into part writing. There are fewer guidelines for how these work. You can usually double whatever you want, except for the leading tone. And they help you write longer phrases, more varied progressions, and melodic bass lines.

Triads more common in First Inversion

Surprisingly, some triads happen more often in first inversion than in root position. These include the leading-tone and supertonic triads (vii°⁶, ii⁶, and ii°⁶).

In vii°⁶, make sure you double the bass note (the third: Re).

Common progressions with First Inversion

• I–V⁶–I
• I–vii°⁶–I
• I–vii°⁶–I⁶
• I⁶–vii°⁶–I
• I–I⁶–IV
• ii⁶–V
• iv⁶–V

Notice these progression create a mostly step-wise bass. Many more possibilities!

Prolongation and First Inversion

One of the main purposes of first inversion triads in classical tonal music is to prolong functions beyond one chord. This lets you write longer phrases of music and have a more interesting bass line. First we can prolong a function with an inverted version of the same chord.

Voice Exchange

The most common prolongational use of first inversion is to write a root position chord followed by the same triad in first inversion. For example in I–I⁶, the B moves from Do to Mi. Composers commonly take the voice singing Mi in the first chord down to Do to still double the root and have movement in two voices. This exchanging of notes between two voices is called voice exchange.

I–I⁶ (i–i⁶)

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

Note the voice exchange has us double the root in both chords. We can do this progression in reverse: I⁶–I (i⁶–i). We can also do this progression on any root position triad and its own first inversion (V–V⁶, etc.).

Neighbor V⁶

We can also prolong functions with chords from other functions. We’ve seen this already with I–IV–I, where IV functions as a tonic prolongation. Using first inversion, we take the strong progression, and turn it into I–V⁶–I to create a stepwise bass and prolong the tonic function. Because of the Do-Ti-Do in the B, we can call this chord a Neighbor V⁶.

I–V⁶–I (i–V⁶–i)

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

Note the doubled Fifth in V⁶ (Re), which gives us the smoothest part writing (no leaps).

Supertonic in First Inversion

As we saw in Part Writing Subdominant and Supertonic, ii⁶ and ii°⁶ are more common than the root position versions.

I–ii⁶–V–I (i–ii°⁶–V–i)

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