Seventh Chord Inversions and Figures

A triad has three chord tones, so it has two inversions. A seventh chord stacks a fourth note a third above the seventh, giving four chord tones: root, third, fifth, and seventh. That means four possible bass notes, so four positions: root position, and first, second, and third inversion.

The figures name the intervals above the bass, counting from the closest tone up. Root position is just "7" because the seventh above the bass is the only interval worth flagging, the rest is assumed. First inversion puts the third in the bass, so the chord tones stack up as a sixth and a fifth above it, written 6 5. Second inversion puts the fifth in the bass, giving a fourth and a third above it, written 4 3. Third inversion puts the seventh itself in the bass, giving a fourth and a second above it, written 4 2. Each figure is really a fingerprint: whichever tone is missing from the top of the stack tells you which tone fell to the bottom.

This sits right after triad inversions, and the logic is identical, just with one more tone to track. Once you can read 6 5, 4 3, and 4 2 as fast as 6 and 6 4, you are ready to see how seventh chords resolve, especially the dominant seventh, where the seventh itself wants to fall by step. Inversions also let a bass line move smoothly instead of leaping between roots, which is why they show up constantly in real part writing.