Introduction to Species Counterpoint

Species counterpoint is a pedagogical method for learning to combine melodic lines, codified by Johann Joseph Fux in his 1725 treatise Gradus ad Parnassum. The method works by adding a composed line — called the counterpoint — against a given melody called the cantus firmus. The cantus firmus is a slow-moving sequence of whole notes, and the five "species" introduce rhythmic complexity in stages, from note-against-note motion all the way to the florid mix of the fifth species.

The rules of species counterpoint are grounded in a fundamental distinction between consonance and dissonance. Consonant intervals — unisons, thirds, fifths, sixths, and octaves — are stable and may be used freely on strong beats. Dissonant intervals — seconds, fourths (in two-voice writing), sevenths, and their compounds — are unstable and require careful preparation and resolution according to the rules of each species. This consonance-dissonance framework is not arbitrary; it reflects the acoustic properties of the intervals and the stylistic norms of 16th-century polyphony.

Motion between voices also governs the rules. Contrary motion (voices moving in opposite directions) is the most independent and is generally preferred. Oblique motion (one voice stationary, the other moving) is safe and useful. Similar motion (both voices moving in the same direction) is acceptable but requires caution. Parallel motion in perfect intervals — parallel fifths or octaves — is strictly forbidden because it merges the two voices into one, destroying the independence that counterpoint is designed to cultivate.