A. Given that both lines are to fulfill the requirements for a good Species line, the following harmonic restrictions apply:
1. When the voies move together in the same note-values, whatever they may be, Species I harmonic relationships are required; that is, the vertical intervals must be consonant.
2. Every half-note position, weak or strong, must have a consonance; the only exception is when there is a dissonant suspension.
3. The dissonant passing-tones or dissonant neighbor tones of Species II/III may only appear at even quarter positions; if two half-notes appear against a whole note, both must be consonant.
4. Dissonant neighbor tones should be avoided. A dissonant neighbor may occur at an even quarter position provided that it is in a group of three or more quarters against a sustained tone a dotted half or longer in the other voice. It may not form an augmented fourth, augmented second, major seventh, or minor second against the sustained voice.
5. An accented passing tone may be used as part of the preparation for a suspension: this is its only use.
6. Species IV relationships between the two voices are good and characteristic. They must, however, be in the proper rhythmic value: that is, where one voice has a series of whole notes, each of which enters at the weak half position, the other voice will have a series of whole notes, each of which enters at a strong half position.
B. Each voice individually should be governed by the melodic and rhythmic considerations applicable to a Species V line:
1. Whole-note values may begin at a weak half position.
2.Dotted half-notes may begin at any half-note position: they may NOT begin at a weak quarter position. That means that dotted half values must be followed by an odd-quantity series of quarter notes (up to a total of seven).
3. Values larger than a whole note should not ordinarily be used except at the beginning of a piece or in one voice at the phrase-final cadential octave or unison.
C. Just as consonances regulate the harmonic relationships between the parts, so also the rhythmic relationship is of considerable significance. The pattern of successive entrances of tones, of successive attacks, in the two voices taken together might be called their "composite rhythm." Whatever may be the individual rhythms of each line, when added together the pattern of attacks throughout both parts should have the following time values:
1. Half and longer time values, in which case we may call it long duration composite rhythm.
2. Half and shorter time values, in which case we may call it short composite rhythm.
3. The pattern, dotted half plus single quarter note may be construed as belonging to either composite rhythm.
4. Composite rhythms of whole notes and quarter notes together should not occur.
5. Composite note values in a long duration rhythm should enter at a strong half position and should appear only at the beginning and for the final cadential sonority. As a rule, once a shift has been made to short-duration composite rhythm within a phrase, long-duration composite rhythm should not appear again until the approach to the cadence, except as part of a dissonant suspension or a 5-6 sequence (above) or 6-5 (below) in Species IV relationship.
1. Each full phrase should end with an octave or unison cadential sonority. For the most part, the cadential sonority should be reached as a conclusion of a suspension cadence. Suspensions may, of course, be made in mid-phrase, but their special place is at the cadence. They increase the amount of dissonance in the texture and slow up the composite rhythm in preparation for hte final subsidence of the phrase to an octave or unison.
2. Suspensions are handled exactly as in Species counterpoint. The suspending voice- the voice which sustains into the dissonance and them resolves downward by step or half-step- may be either the upper voice (7-6 or 4-3) or the the lower voice (2-3). The sequence of events begins with preparation at the weak half position and resolution at the weak half position of the next measure.
3. The accented passint tone of an ornamented preparation must be a descending passing tone only, filling in the interval of a downward melodic third. Furthermore, the preparation-consonance, whihc is now displaced to an even quarter position just before a strong half, must move back upward stepwise to produce the dissonant second, seventh, or fourth of the suspension. The pattern of the two voices in the ornamented suspension is: