Species counterpoint, and the method that isolates one variable at a time
The classical method of writing independent lines against a cantus firmus, one restriction at a time — first pitch alone, then rhythm, then dissonance; the school where voice leading was formulated.
Counterpoint is the art of writing two or more lines that are each a melody and that together make sense. The method by species, fixed by Fux in 1725 and used ever since, teaches this by isolating one variable at a time: first the pitches alone, note against note; then rhythm, two notes against one; then dissonance, controlled; and only at the end everything together. Each species adds one freedom and one rule.
The cantus firmus
Everything starts from a given melody, the cantus firmus, in semibreves, eight to twelve notes long, beginning and ending on the tonic and moving almost entirely by step. Against it the other voice is written, above or below. The given melody does not change; the exercise is what you put against it.
A cantus firmus in C: eleven notes, a single leap, beginning and ending on the tonic.
First species: note against note
One semibreve against each semibreve. Consonances only: unison, third, fifth, sixth, octave, and no fourth, which in two-voice counterpoint is a dissonance. The rules of movement:
- Begin and end on a perfect consonance: unison, fifth or octave.
- Prefer contrary and oblique motion; direct motion sparingly.
- Never approach a fifth or an octave by direct motion, and never two fifths or two octaves in a row.
- Prefer imperfect consonances, thirds and sixths, in the middle, because the perfect ones sound hollow.
One solution above the cantus: octave, sixth, third, third, third, third, third, third, third, sixth, octave. Contrary motion at the edges, thirds and sixths in the middle, no perfect parallels.
Second species: two against one
Two minims against each semibreve. The first of each pair falls on the strong beat and must be consonant; the second, on the weak beat, may be dissonant if it is a passing tone, arriving and leaving by step. It is the first controlled appearance of dissonance, and the rule says exactly where it may be.
Third species: four against one
Four crotchets against each semibreve. More rhythmic freedom, and dissonance still only passing or neighbouring, always by step, never on the first beat. The nota cambiata also appears — a four-note figure with a leap of a third away from a dissonance — which the tradition accepts because the ear accepts it.
Fourth species: the suspension
Minims tied across the barline: the weak-beat note is held into the next strong beat, where it becomes a dissonance, and resolves downward by step. That is the suspension, the most expressive dissonance in counterpoint, and this species teaches it in its pure state: consonant preparation, dissonance on the strong beat, resolution downward.
Fifth species: florid counterpoint
Everything together: mixed values, passing tones, neighbour tones, suspensions, with each species' rules holding wherever the corresponding figure appears. It is free writing with the restrictions internalised, and it is the goal of the whole path.
What to take from here
Species counterpoint is writing against a cantus firmus with one more freedom per species: consonant pitches, then rhythm with passing dissonance, then four notes, then the suspension, then everything. The rules — perfect consonances at the edges, contrary motion, no parallels, dissonance only by step and in the right place — are those of voice leading in their purest form, and this is where they were formulated.