Chord Inversions and Figured Bass

A triad's notes don't have to stay stacked root-third-fifth from the bottom. Put the third in the bass instead and it's called first inversion; put the fifth in the bass and it's second inversion. The chord — its letter names — hasn't changed, only which note is lowest.

This matters because the bass note is what the ear locks onto as the harmonic "floor." A root-position C major triad (C in the bass) sounds planted and final; the same three notes in first inversion (E in the bass) sound lighter and more transitional — useful for keeping a bass line moving stepwise instead of jumping between chord roots.

Figured bass notates inversions with small numbers under (or after) the bass note, inherited from Baroque-era shorthand: root position is unmarked (or ⁵₃), first inversion is ⁶ (a sixth above the bass), second inversion is ⁶₄. In Roman numeral analysis you'll often see this folded in directly: I, I⁶, I⁶₄.

Second inversion is the odd one out — it's treated as dissonant in traditional voice leading (the fourth above the bass wants to resolve) and shows up almost exclusively in specific formulas: passing motion between two other positions, or the cadential ⁶₄ that decorates a dominant chord right before a cadence.