Textbooks traditionally teach that there are four types of six-four (i.e., second inversion) chords:
- Pedal six-four (also sometimes called neighbor), where the bass stays the same;
- Passing six-four, where the bass functions as a passing note between two harmonies;
- Cadential six-four, a specific type of pedal six-four that occurs over scale-degree 5;
- Arpeggiated six-four, where the bass arpeggiates the given harmony.
I've always been a little skeptical of the arpeggiated six-four—in the interests of full disclosure, I just plain don't think it even exists—and I'm unsure why we view some six-four chords as arpeggiated and others as just expanding a more stable inversion of the chord.
Consider, for instance, the following two examples:
The above Beethoven example is almost invariably cited in textbooks as a perfect example of the arpeggiated six-four. Here, I've labeled these chords with asterisks below the staff.
But to me, the Beethoven example is hardly any different from the following Mozart example, and no one in their right mind would label every inversion of this Alberti bass:
Can anyone explain to me the logic here? If the Mozart example isn't an arpeggiated six-four, why is the Beethoven example? It can't be an issue of tempo or the rate of pitch change, because that doesn't matter in other aspects of tonal theory.