Or first-inversion chords as my classical friends will be accustomed to thinking of this. This is a sonority that is very normal in classical harmony, used frequently to help make the bass line melodic, and very unusual in barbershop harmony, where you can go entire songs without encountering it. (Conversely, the 2nd inversion – basses on the 5th – is entirely normal in barbershop, but hedged about with all kinds of voice-leading rules in the classical world.) One of the things this post will explore is the reason for this difference in frequency in the two worlds, as well as reflecting on the character of the sonority in itself.
In both worlds, the first inversion has a distinctive character, more poised to move on, than the settled quality of root-position chords. In part this is due to its melodic function – it often appears mid-way in a line’s route from starting-point to cadence. But it’s also about the sonority itself, and the acoustic needs for balance. This in turn will reveal why it is used so much less in barbershop music than classical, and why it therefore has a disproportionately significant impact when it is used.