How to Harmonize with Second Inversion Chords

In this lesson, we’ll focus on using second inversion triads in four-voice harmony. If you need to review triads, and their various inversions, see this music theory lesson.

Second Inversion Triads

When the fifth of the chord is in the bass (the lowest note of a chord), it is said to be in second inversion. In four-voice harmony,the bass is always doubled in one of the upper voices (SAT), following the standard doubling procedures.

In traditional tonal harmony, second inversion triads are somewhat restricted in their use. In fact, when you write four-voice harmony, there are only three instances where a second inversion triad may be used.

Play any second inversion triad and listen carefully to the bass. The chord tends to be unstable due to the 5th of the chord being in the bass. This instability is why second inversion triads must be handled carefully in harmonic progressions. Listen to The Star-Spangled Banner and take note of the second inversion triads that are marked on the score. This anthem contains examples of the two most common types of second inversion triads:

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The Cadential Six-Four Chord

The cadential six-four chord is a tonic chord in second inversion. The following conditions must be met when using this chord in traditional harmony:

It must precede a dominant (V) chord
It must occur on a stronger beat than the dominant chord that it precedes
When resolving to the dominant, keep the two common tones ( in the bass and one of the upper voices) and move the other two voices down by step

Notice how all of these conditions are met in The Star-Spangled Banner:

(* The notes in parenthesis are non-chord tones, that is, notes that don’t belong to either of the chords. Non-chord tones are common in all music; we’ll get to them in a future lesson. Also, the last dominant chord actually is a V7, in the alto moving down to the 7th of the chord. This also is an acceptable resolution of the cadential six-four, but not quite as common.)

The Passing Six-Four Chord

In contrast to the cadential six-four chord, the passing six-four chord occurs on a weak (unaccented) beat between a root-position chord and its first inversion. It gets its name, passing, from the fact that it passes between two different positions (root position and first inversion) of the same chord. Another feature of the passing six-four chord is a voice exchange between the bass and one of the upper voices (usually the soprano).

The example in The Star-Spangled Banner is the most common type of passing six-four chord: a dominant (V) six-four chord between a root-position tonic triad and a first-inversion tonic triad. The voice exchange is in the bass and soprano; the bass moves from A-flat up to C, while the soprano moves from C down to A-flat:

The Pedal Six-Four Chord

The bass of the pedal six-four chord stays on the same note while two of the upper voices move up by step, then back down to the same chord:

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The name pedal comes from a typical device used by organists, where the foot pedal is held while changing harmonies on the keyboard manuals. Because two of the upper voices move up by step, then back down, the chord is sometimes referred to as a neighboring six-four chord.

The opening of Mozart’s Piano Sonata in C, K. 545 has a pedal six-four chord:

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Progressions Using Six-Four Chords

Following are common progressions using the different types of six-four chords. You can download pdf versions of these progressions written out in every major and minor key on the Harmonic Progressions Page.

I-IV-I6/4-V-I (Cadential six-four)
I-V6/4-I6-V6/4-I (Passing six-four)
I-IV6/4-I (Pedal six-four)
I-V6/4-I6-IV-I6/4-V-I-IV6/4-I (This progression combines all three six-four chords)