​​​​​​​​​Second Inversion Triads (Six-Four Chords)

Second Inversion is surprisingly rare for triads in common practice music. The reason is that these chords sound unstable in a tonal environment. Play one on a keyboard. Do you feel it need to resolve? If so, move the upper two notes down by step. Is that better? This sensation is why common-practice composers treat these triads with care. They only use them in particular ways to make them sound normal.

As we analyze these chords in music and write them ourselves, we want to recognize these specific ways second inversion triads are used. To do this we add an extra label underneath the normal Roman numeral plus inversion symbol. Make sure you always include these new labels that show the type.

The important points:

  • To determine the six-four chord type, look at the bass voice.
  • When part writing, double the Bass (the fifth of the chord).
  • With the exception of the cadential six-four, the rest can appear on any chord that might make sense. In other words, the roman numerals aren’t consist; the voice-leading shape is.

Neighbor Six-Four (Pedal Six-Four)

This chord has three of the same bass note in a row, or longer held notes, while two upper voices move up by step into the six-four chord and down by step out of the six-four chord. Notice that the upper voices make a shape like a neighbor tone.

A common example: IIV64I

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

We add the following label under the six-four Roman numeral: N64.

Passing Six-Four

This chord has three notes in a row that ascend or descend by step, shaped like a passing tone.

A common example: IV64I6.

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

We add the following label under the six-four Roman numeral: P64.

Cadential Six-Four

Although this chord has Do and Mi in it, it has a dominant function. It is always a tonic six-four that goes immediately to a dominant. It is usually preceded by a predominant, such as IV or ii6.

I64-V

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

Labeling the Cadential Six-Four

Now when it comes to labels, there are two schools of thought that agree on a basic premise. We want to recognize that this chord has a dominant function. So, how do we show this in our label?

  • One idea, familiar from the Kostka/Payne Tonal Harmony book, is to retain the same Roman Numerals I use above and then to use a bracket and another V to show their shared dominant function.

  • The other, followed by our Roig-Francoli Harmony in Context book, takes the dissonant nature of this moment as primary. It focuses on the melodic voice-leading and uses figures simiar to the ones we see when labeling suspensions. This gives us a single Roman numeral V and adds 6-5 and 4-3 to show the melodic descent in two voices over the stationary Bass. The octave-leap version shown below is also common.

The choice of labels here can get surprisingly heated if theorists are so unpolite to bring this up. Anyway, pick the one you think makes sense, and use it. I don’t care which one.

Arpeggiated Six-Four

This just means you see the fifth in the bass at some point during a long prolongation of the same chord. I probably will never mention this again.

Finding and Labeling Six-Four Chords in Music

  1. You have found a major or minor triad in second inversion.
  2. Then look at the bass line including the two chords surrounding the six-four chord.
  3. Then you have three options:
    1. The three bass notes are the same: Neighbor.
    2. The three bass notes follow two rising or falling steps: Passing.
    3. You have a I64 followed by a V: Cadential.
  4. Label the chord with the chord Roman numeral, inversion label, and six-four chord type label.