What changes compared with two voices
With three voices note against note, harmonic sonority appears: every vertical is a chord. Fux asks us to seek, when possible, the complete triad (root, third, fifth) or its alternative with the sixth in place of the fifth (first-inversion chord, 6/3). The rules of motion remain, but some are relaxed, because it is impossible to satisfy them all with three singable lines.
Rules
- Consonant verticals against the bass: third, fifth, sixth, octave. The fourth is admitted only between the two upper voices.
- Complete triad when possible; if an element is missing, preferably omit the fifth, almost never the third.
- No 6/4 (fourth and sixth above the bass).
- First and last bar: may contain the third; in the final chord the third, if present, is major (F# in D, G# in Aeolian; B in Mixolydian is already major).
- Parallel fifths and octaves forbidden between every pair of voices.
- Hidden fifths and octaves: to be avoided between the outer voices; between an inner voice and an outer one they are tolerated if one of the two moves by step.
- Unison: admitted also in the internal bars when it helps the voice leading, but sparingly.
- Motion: avoid all three voices moving in the same direction.
- Spacing: no more than an octave between the upper voices; the bass may be farther away.
Example in D Dorian, cantus in the bass
| Bar | Bass (cantus) | Middle voice | Upper voice | Chord |
|---|---|---|---|---|
| 1 | D3 | D4 | A4 | D (5 and 8) |
| 2 | F3 | C4 | A4 | F complete |
| 3 | E3 | C4 | G4 | C/E (6/3) |
| 4 | D3 | D4 | F4 | Dm without fifth |
| 5 | G3 | B3 | E4 | Em/G (6/3) |
| 6 | F3 | C4 | A4 | F complete |
| 7 | A3 | C4 | E4 | Am complete |
| 8 | G3 | B3 | G4 | G without fifth |
| 9 | F3 | C4 | A4 | F complete |
| 10 | E3 | E4 | C#5 | E with sixth (cadence) |
| 11 | D3 | F#4 | D5 | D major without fifth |
- Bar 5: E4 over B3 forms a fourth between the upper voices, accepted because the bass G3 supports it with a third and a sixth.
- Bars 9–10: parallel sixths between the middle and upper voices (C4/A4 → E4/C#5), in contrary motion to the bass.
- Cadence: the bass makes the tenorizans E–D, the soprano the cantizans C#–D, the middle voice rises from E4 to F#4.
Cantus in the other positions
- Cantus in the middle: the bass must begin and end on the finalis; in the cadence the bass often leaps A–D (bassizans) while the cantus goes E–D.
- Cantus on top: the bass below must begin on an octave or unison with the finalis; the middle voice fills in the triad.
In all cases the voices remain singable: an incomplete triad is better than a leap of a seventh.
Typical errors
- Chasing the complete triad with ugly leaps in the middle voice.
- Doubling the leading tone (C# in two voices) in the penultimate chord.
- Writing fourths between the bass and the upper voice thinking they are consonant.
- Leaving the middle voice still for many bars: it becomes an unintended pedal.
Modern application
- Three-part choirs (SAB or TTB): first species in three voices is the grammar of syllabic arrangements; the rule of the fourth between upper voices allows open, modern voicings.
- Pop: a trio of backing vocals moving note against note under the melody works like this species; keep the arrangement's bass in contrary motion to the highest voice.
- Soundtracks: chorales for three horns or three trombones use the complete triad and the 6/3; the cadence with the final major third gives a bright closure.
Related topics
Three-part counterpoint, consonances in strict counterpoint, modal clausulae and cadences, florid species in three voices.