Music Theory/Counterpoint/Species Counterpoint/In Two Voices

Cantus Firmus
One contrapuntal line is always composed against another given line. This given voice is called the cantus firmus. This line may be taken from a book of chorales, as Fux suggests, may be provided by a teacher, may be composed by the student him/herself or may be taken from the work of a master.

Consonance
In writing counterpoint, it is important to note which consonances are being formed, for they produce what the ear hears as harmony. Fux lists five consonances, in two categories, to be used in the writing of counterpoint according to the rules he has laid down.


 * Perfect Consonances : Include the unison and octave, along with the fifth


 * Imperfect Consonances : Include the major/minor third, and the major/minor sixth


 * Dissonances : Include the major/minor second, the fourth, the augmented fourth, the diminished fifth, and the major/minor seventh

Motion
Motion in music is what creates interest. The establishment of tonal relationships is impossible without it, and the harmony created by the melodic motion of independent voices is what establishes these relationships. There are only three kinds of motion possible in one voice relative to another.


 * Direct Motion : The voices move in the same direction by stepping or skipping. Parallel Motion is a subset of Direct Motion wherein both voices move in the same direction by the same amount (the vertical interval between them does not change).


 * Contrary Motion : One voice moves up in pitch while the other moves down in pitch.


 * Oblique Motion : One voice moves up or down by step or skip while the other voice does not move.


 * Similar Motion : The voices move in a similar manner, i.e. one voice moves up a fifth while the other moves up a third.

Variety is important in music. This holds true for rhythm, harmony and melodic motion. Judicious use of the three types of motion creates variety and helps minimize the possibility of motivic stagnation.

General Rules
Fux's rules about contrapuntal motion under specific circumstances are four in number.


 * First Rule : Only proceed from perfect consonance to perfect consonance in contrary or oblique motion.


 * Second Rule : Any of the three motions is permitted if moving from a perfect consonance to an imperfect consonance.


 * Third Rule : Only proceed from imperfect consonance to perfect consonance in contrary or oblique motion.


 * Fourth Rule : Any of the three motions is permitted if moving from an imperfect consonance to an imperfect consonance.

Those who read closely may find that these four rules may be condensed into a single rule.


 * Rule : Any motion is allowed except for the direct motion into a perfect consonance.

Progressing into the subject of counterpoint, several other "general rules" exist. These usually regard perfect consonances in one way or another. However, direct motion into perfect consonances will always be forbidden in the Common Practice style.

First Species - Note Against Note
First Species counterpoint is note against note counterpoint. That is to say that for every note in the cantus firmus there is one note in the added harmony. Rules for species counterpoint are grouped hard and soft. Hard rules may not be broken whereas soft rules may be broken if it will avoid violating a hard rule, though the better solution is one that breaks no rules.

The hard rules:

1) For every note of the cantus firmus there is one note in the counterpoint

2) No accidentals may be used (except rule 5)

3) All harmonies must be consonant (a perfect fourth is considered a dissonance)

4) The first interval must be any perfect harmony and the last an octave or unison

5) The last interval must be approached by motion of a minor second upwards (note rule 7 may not be broken)

6) All perfect intervals must be approached by contrary motion

7) Motion can proceed by step or leap but steps and leaps of augmented and diminished intervals and leaps of any seventh are forbidden. Leaps greater than a sixth are forbidden except for leaps of an octave which should be rare

8) The counterpoint may not outline an interval of a tritone or seventh except for an augmented fourth that is fully, stepwise outlined and precedes an inwards step

The soft rules:

1) No note may be repeated successively more than three times

2) No two successive leaps in the same direction may total more than an octave

3) While ascending, in the case of two successive steps or leaps, the larger one should precede the smaller; while descending the smaller should precede the larger

4) No successive leaps in opposite directions; leaps should be followed by inward, stepwise motion

5) The same harmonic interval should not repeat more than three times

6) There should be no more than two successive leaps

7) The range of the counterpoint should be limited to a tenth and all notes in the chosen mode should appear in the counterpoint