Third species — four against one

Four notes against one. The first quarter of each bar is consonant; the remaining quarters move mostly by step, and dissonance is admitted where the line passes through it — including the run of four that traverses a seventh between two consonances. Out of this species come the named figures — the passing run, the neighbor, the cambiata — because at four to one the line is fast enough to decorate and still slow enough to be judged note by note.

Where figuration is learned: at four notes to one the counterpoint becomes genuinely melodic, and each bar is a small study in how a line traverses, decorates, or circles its consonances. The figures codified here — run, neighbor, cambiata — are the working vocabulary of every diminution, division, and ornamented chorale that came after.

• Opening a bar on a dissonance, when the first quarter must be consonant.
• Leaping into or out of a dissonant quarter that is not the cambiata’s licensed leap.
• Writing the four quarters as arpeggios bar after bar, which turns counterpoint into broken chords.
• Letting the quarters outline a tritone across the bar.
• Approaching the final by leap instead of step.

• Johann Joseph Fux, Gradus ad Parnassum (1725), Liber secundus, third species — The quarter-note species: figuration under strict per-quarter interval discipline.
• Luigi Cherubini, Cours de contrepoint et de fugue (1835), Third species, two-voice counterpoint — The Conservatoire treatment of the same figures and their placement.