Inversion

Inversion changes a chord’s function without changing its identity. Root position is stable and conclusive; first inversion is lighter and keeps the music moving; second inversion is unstable and usually wants to resolve, which is why it appears so often just before a cadence.

This matters directly to cellists and bassists, because the bass line is what decides the inversion. The same harmony sounds settled or restless depending on which note the bottom of the texture takes, and a bass player who understands that plays the line with intent rather than as a set of pitches.

Intervals invert too: a third inverted becomes a sixth, a fourth becomes a fifth, and the two numbers always sum to nine.