Counterpoint (from Latin punctus contra punctum — “note against note”) is when each voice has its own line, yet all together they form a harmonious whole.
The pinnacle of the contrapuntal art is J.S. Bach. His Art of Fugue and Musical Offering are composition textbooks for generations to come. Counterpoint demands that a composer think horizontally and vertically at once: each melody is self-sufficient, but their combination builds the harmony.
The rules of classical counterpoint were systematised by Johann Joseph Fux in his treatise Gradus ad Parnassum (1725), which breaks the technique into five “species” — from note-against-note to florid counterpoint. Haydn, Mozart, and Beethoven all studied from this manual. Key contrapuntal devices include imitation, inversion (turning the melody upside down), retrograde (moving backwards), and the augmentation/diminution of the theme's note values.
