### Contrapuntal techniques

Isaac employs systematic contrapuntal techniques notated with symbols or canonic rubrics in many sections of *Choralis Constantinus II*. The instructions for these techniques are never cryptic. In the case of imitation canons, the time interval and first pitch of the *comes* voice are indicated with rests and a custos. Other techniques are specified with clear verbal instructions. Most of the canons are based on the melody of the cantus firmus.

Techniques involving cantus firmus treatment, including multiple cantus firmi, are discussed under *Cantus firmus treatment*.

#### Imitation canons

Two voices:

- Introit 6, verse (T/A - upper fourth)
- Alleluia 20, verse (T/A - unison)
- Sequence 3, v. 8 (A/T - unison)
- Sequence 4, v. 4 (D/A - lower fifth)
- Sequence 4, v. 6 (B/T - upper fourth, written out because of changed time interval within the verse)
- Sequence 4, v. 8 (T/A - upper fourth)
- Sequence 6, v. 18 (T/D - upper octave; no overlap)
- Sequence 7, v. 8 (T/D - upper octave)
- Sequence 8, v. 2 (B/T - upper octave)
- Sequence 8, v. 8 (D/T - lower octave)
- Sequence 8, v. 10 (B/T - upper octave)
- Sequence 8, v. 14 (A/T - lower fourth)
- Sequence 8, v. 20 (D/T - lower octave)
- Sequence 9, v. 18 (A/D - upper fifth)
- Sequence 12, v. 14 (A/D - upper fifth)
- Sequence 13, v. 6 (B/A - upper octave)
- Sequence 13, v. 16 (B/T - upper fourth, written out)
- Sequence 16, v. 6 (T/B - lower fifth)
- Sequence 16, v. 8 (B/A - upper fifth)
- Sequence 16, v. 10 (T/D - upper octave)
- Sequence 17, v. 8 (T/A - unison)
- Sequence 18, v. 10 (D/T - lower octave; see also Systematic doubling below)
- Sequence 19, v. 2 (D1/D2 - unison)
- Sequence 19, v. 20 (T/B - lower fifth)
- Sequence 20, v. 22 (B/T - upper fifth)
- Sequence 22, v. 8 (T/D - upper twelfth)
- Sequence 22, v. 16 (T/B - lower fourth)
- Sequence 23, v. 22 (T/D - upper octave)
- Sequence 24, v. 8 (B/T - upper fifth)
- Tract 5, v. 2 (A/T - lower fifth)
- Communion 1 (B/T - upper fourth)
- Communion 18 (T/D - upper octave)

Three voices:

- Sequence 18, v. 2 (B/T/D - upper octave, upper double octave)
- Sequence 25, v. 10 (T1/D/T2 - upper octave, unison)

Four voices:

- Sequence 10, v. 16 (A/B/D/T - lower octave, upper fourth, lower fifth)

#### Double imitation canons

- Sequence 4, v. 2 (A/D - upper fourth; B/T - upper fourth)
- Sequence 10, v. 8 (T/D2 - upper octave; A/D1 - upper octave)
- Sequence 16, v. 20 (D/T - lower octave; B/A - lower octave)
- Tract 4, v. 4 (A/D - upper fourth; B/T - upper fourth)

#### Retrograde canons

- Sequence 15, v. 2 (D-[₵]/T-
*in duplo*- lower octave)

- Alleluia 20 (A/T - unison)
- Sequence 10, v. 12 (D/T - lower octave)

#### Augmentation canons

- Sequence 9, v. 2 (D-Օ/T-Ꙩ - lower octave)
- Sequence 15, v. 2 (D-[₵]/T-
*in duplo*- lower octave) - Sequence 22, v. 4 (A-₵/D-
*crescit in duplo*- upper octave) - Sequence 22, v. 6 (T-₵/B-
*crescit in duplo*- lower octave)

#### Systematic doubling of voices

- Introit 20, verse (D/A, parallel fourths)
- Sequence 18, v. 10 (T/V, parallel thirds; see also Imitation canons above)
- Sequence 21, v. 12 (B/T - parallel thirds)

#### Systematic repetition of melodic segments

- Sequence 25, v. 8 (D; double bars function as repeat signs)
- Communion 25 (A/B; double bars function as repeat signs)