What changes compared with three voices
In four voices note against note, the sonority is almost always a complete chord with one doubled note. The difficulties increase: six pairs of voices to check, little room to move. For this reason Fux grants some freedoms that were not allowed in two and three voices, especially in the inner voices.
Rules
- Verticals: every voice consonant with the bass; fourths are admitted between the upper voices.
- Complete triad where possible, with one doubled note: preferably the root; in the 6/3 the third or the sixth above the bass is gladly doubled. Never the raised leading tone.
- First and last bar: chord on the finalis, with or without the third; the final third, if present, is major.
- Parallels: fifths and octaves forbidden between every pair.
- Hidden: forbidden between the outer voices (bass and soprano); tolerated between an inner voice and the bass, especially when the upper voice of the pair moves by step and in cadences.
- Spacing: at most an octave between soprano and alto and between alto and tenor; the bass may be farther from the tenor.
- Motion: never all four voices in the same direction; seek contrary motion between bass and soprano.
- Crossings and unisons: possible for short stretches in the inner voices, if they improve the lines.
- Repeated notes: admitted in the inner voices; they serve to hold the chord still.
Example in D Dorian, cantus in the tenor
| Bar | Bass | Tenor (cantus) | Alto | Soprano | Chord |
|---|---|---|---|---|---|
| 1 | D2 | D3 | D4 | A4 | D (open) |
| 2 | A2 | F3 | C4 | F4 | F/A |
| 3 | C3 | E3 | A3 | A4 | Am/C |
| 4 | B2 | D3 | B3 | G4 | G/B |
| 5 | E2 | G3 | C4 | G4 | C/E |
| 6 | F2 | F3 | C4 | A4 | F |
| 7 | D2 | A3 | D4 | F4 | Dm |
| 8 | E2 | G3 | B3 | E4 | Em |
| 9 | F2 | F3 | A3 | D4 | Dm/F |
| 10 | A2 | E3 | A3 | C#4 | A |
| 11 | D2 | D3 | F#3 | D4 | D |
Observations:
- Bass: D2 A2 C3 B2 E2 F2 D2 E2 F2 A2 D2, a true bass line with leaps of a fifth and a fourth alternating with steps. Many chords are in first inversion (bars 2–5): the 6/3 lets the bass move by step under the cantus.
- Soprano: A4 F4 A4 G4 G4 A4 F4 E4 D4 C#4 D4, final descent by step toward the cantizans C#–D.
- Alto: fills in the chords with small movements and repeated notes (C4 in bars 5–6, A3 in bars 9–10).
- Contrary motion between the outer voices in the passage 1–2 and throughout the final section (bars 7–11): the bass rises while the soprano descends toward the cadence, then the two voices close on the finalis.
- Cadence: bass A2–D2 (bassizans), tenor E3–D3 (tenorizans), soprano C#4–D4 (cantizans), alto A3–F#3 bringing the major third. The hidden octave between tenor and bass in the last bar is the typical freedom of this formula.
How to work
- Write bass and soprano against the cantus first, like a three-part counterpoint.
- Add the missing voice, choosing the note that completes the chord with the smallest movement.
- Check the six pairs for fifths and octaves.
- Sing every voice: the inner voices can be simple, but not clumsy.
Typical errors
- Doubling the C# in the penultimate chord.
- Inner voices leaping a sixth to complete the chord.
- Tenor and alto more than an octave apart.
- Parallel fifths between alto and tenor, easy to miss because they are hidden in the middle of the score.
Modern application
- SATB choirs: this is the basis of homorhythmic choral writing; the spacing rule avoids holes in the sound.
- Pop: for a four-part arrangement of backing vocals, starting from the bass of the harmony and the melody, then filling in with the inner voices, is the same procedure.
- Film brass and strings: chorales for four horns or four trombones follow these rules; the 6/3 with stepwise bass gives a singable bass line even in a slow chorale.
Related topics
Four-part counterpoint, SATB writing, first species in three voices, florid species in four voices, modal clausulae and cadences.