(musth1) First Inversion Triads

Uses and Function

Triads in first inversion provide the following uses and function:

• They expand the number of possible bass pitches, thereby providing the opportunity for melodic bass lines.
• They allow for greater hierarchy of function by avoiding root position V – I movement away from cadences.
• They provide more prolongation opportunities through root to first inversion movement (and vice versa).

Prolongation and Voice Exchange

Moving from root position to first inversion (and vice versa) are often accompanied by a voice exchange between the soprano and bass lines. In a voice exchange of this sort, the inner voices remain unchanged. The soprano moves to the chord tone that the bass previously had, and the bass moves to the chord tone the soprano previously had.

If you start with a root position triad, say a tonic chord, place the third in the soprano. The root will be in the bass. Moving to a first inversion triad of the same type, the bass will move from the root to the third of the chord. The soprano can then move down from the third to the root of the chord.

Prolongation and the V6

Using a V6 between two tonic triads provides another possible tonic prolongation progression. Instead of labeling the movement according to the soprano motion, we refer to the lower neighbor motion in the bass line (scale degrees 1 – 7 – 1).

Parallel First Inversion Triads

First inversion triads in close position do not have a perfect fifth. This property allows for composers to string together parallel first inversion triads by stepwise movement, usually as part of a transitional passage. When first inversion triads move in parallel motion we do not label them with Roman numerals, because they do not have a harmonic function based on their root. We use the figured bass indication of 6 under each chord, ending with a 5 and the Roman numeral. In other words, we label the harmony of the chord before the parallel first inversion triads, and the chord after the last first inversion triad, but nothing in between.

In four voices you will have parallel octaves in this type of progression. You need to use an alternate doubling technique, where you alternate between doubling the root of one chord, then the third of the next, alternating until the progression of parallel chords has ended.