What is an Inversion (Counterpoint)?

An inversion in counterpoint is a technique in which a melodic line or interval is turned upside down, so that each ascending interval becomes a descending interval of the same size, and each descending interval becomes ascending. This preserves the contour and relationships of the original melody but flips its direction.

For example, if the original subject moves up a major third and then down a perfect fifth, its inversion would move down a major third and then up a perfect fifth. In fugues and other contrapuntal works, inversion allows composers to vary the subject while maintaining its identity and intervallic structure.

Inversion is widely used in Baroque and classical counterpoint, particularly by composers like J.S. Bach, to create contrast, extend thematic development, and maintain interest in polyphonic textures. It allows a theme to be explored in new directions without losing its recognizable character.