Rules For First Species of Strict Counterpoint in Two Parts.
I. Use Consonant intervals only. The Consonant intervals are: The Major and Minor Third, Major and Minor Sixth, Perfect Fifth and Octave. The Unison may be used, but its use is generally restricted to the final note. The Dissonant intervals are: The Seconds and Sevenths, and all Augmented and Diminished intervals. The Perfect Fourth is considered as a Dissonance in two-part Counterpoint.
II. The C.P., when above the C.F., may begin with the Octave or the Fifth; when below the C.F., it must begin with the Octave. The Unison may used at the beginning, but is not considered as good as the Octave. The C.P. must end with an Octave or an Unison. If the C.F. ends (as it generally does) by descending from the second of the scale to the keynote, the C.P. must end by ascending from the leading note to the keynote.
III. The parts must move in opposite directions to a Fifth, Octave, or Unison.
There is one exception to this rule admitted, viz., the third over the (or any) leading note followed by the fifth over the Tonic. The reason being that the fifth over the leading note is Diminished.
IV. The false (or cross) relation of the Tritone (augmented fourth) and of the augmented or diminished octave must be avoided. The false relation occurs when the distance from the lower note of one interval to the upper note of the next interval (or the reverse) is an augmented fourth or an augmented or diminished octave. To avoid the false relation of the augmented fourth, never write in succession the major thirds on the fourth and fifth degrees of the scale.
Never write any of the following successions:
Numbers 1 and 2 are very harsh. Numbers 3 and 4, not so harsh, are of common occurrence in modern usage.
The harshness of the false relation may be avoided as follows:
1. Sub-dominant with third, followed by Supertonic with sixth.
2. Same reversed - not quite satisfactory.
3. Dominant with third, followed by Sub-dominant with sixth.
4. Same reversed - sounds equally well both ways.
The false relation of augmented or diminished octave, is made as follows. It must never occur in two-part C.P.
V. The C.P. must never leap beyond the octave, or leap a seventh of any kind, or any augmented or diminished interval, except the diminished fifth. (The leap of a sixth even is forbidden by the strictest authorities.) The leap of the octave is always good.
VI. The Imperfect Consonances (thirds and sixths, major and minor) should be used in preference to the Perfect. (perfect fifth and octave).
VII. Contrary motion should be used in preference to parallel or oblique.
VIII. Not more than three thirds or sixths should be written in succession: (to avoid monotony).
IX. Chromatic passages must not be written. A chromatic passage occurs when a letter is written twice in succession and altered by sharp, flat, or natural.
The following example is an illustration of the rules just given.
Counterpoint above the Cantus.
1. Fifth in contrary motion.
2. Fifth in oblique motion.
The next example has the C.P. written below the C.F. (which is moved up an octave). The practice of writing the C.P. both above and below the theme must be adhered to, all through the study of Counterpoint.
To save space and aid facility of inspection, two-part C.P. is written, in this work, on one staff, and the time-honored custom of using C clefs is departed from.
The F must be sharp, to avoid a false relation.
Do not be satisfied with writing one C.P. to each theme; write five or six, varying them as much as possible.