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The cantus firmus (c.f.) is a self-contained and balanced melodic line to be used for writing exercises in a system known as species counterpoint. The first task will be to construct a line that has the appropriate qualities:
- Singability (vocal idiom)
- Melodic fluency
- Equilibrium (neutrality, homogeneity)
- Closure
- Goodness of contour
- Coherence
To attain these qualities we will observe certain fixed rules of procedure:
- Maximum range of a 10th (alto or tenor register preferable)
- Only diatonic tones are used (major system only at present)
- All notes are of equal duration (by convention, the whole note)
- No tone-repetitions are permitted
- First and last notes are both tonic, and in same register
- No dissonant leaps are allowed (the P4 is consonant in melody only)
- No leap larger than an 8ve is permitted
- No series of three notes may define a 7th or larger dissonance
- Final tone must be preceded by either degree 7 or degree 2
- Apex (highest tone) must not be the leading tone
- Apex tone must occur only once
We will also keep in mind certain tendencies or preferences:
- Preference for conjunct (stepwise) motion over disjunct
- Preference against two successive leaps in same direction
- When leap is followed by step, preference for direction opposite to that of leap. (Strength of preference increases with size of leap.)
- Preference for variety of type and direction of motion
- Preference against formation of internal groups through registral isolation, sequential repetition, or other means
- Preference for moderation in length (8-15 notes)
Some of these tendencies (e.g. numbers 12 and 15) work at cross purposes to each other. Part of the task of writing the c.f. is to reconcile these opposing forces by using good intuitive judgment.
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Copyright © 1998 by John Rothgeb
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