In the early 16th century, the common modes were Dorian, Phrygian, Lydian, and Mixolydian. By mid-century, the Ionian and Aeolian modes were also frequently used. The practice of Musica Ficta was common, which referred to chromatic inflections that were sung or played, but not notated in the music. In all modes except Phrygian, the leading tone was raised to approach the tonic by half-step at the cadence. In the Dorian and Lydian modes the B was flatted when moving from A to B and back, the upper noted referred to as “una nota supra La.” Consonant intervals appear on accented beats, and dissonances such as passing tones and neighboring tones were allowed on weak beats. The suspension in 4th Species is an exception. The melodic movement is primarily stepwise, with a few leaps that usually turn back in the opposite direction.
P4th above the lowest voice
All augmented and diminished intervals
The unison, P8ve and P5th are the perfect consonances, while 3rds and 6ths are imperfect. The P4th is a special case, always dissonant in two-parts, but consonant in three or more parts between upper voices. The harmonic series and Pythagorian just intonation explains the various uses of a P4th. It only appears early in the series between two upper partials, not above the fundamental. It is advisable to write the number of each harmonic interval between the two parts to avoid unwanted dissonances when composing counterpoint.
Contrary: the voices move in opposite directions
Parallel: the voices move in the same direction with the same interval between them
Similar: the voices move in the same direction with different intervals between them
Oblique: one voice moves while the other is sustained or repeated
Contrary motion provides the most independence, but a variety of these kinds of motion is recommended for a musical result. Fux uses the term “direct” motion to refer to both similar and parallel motion.
Begin with a perfect consonance when the finalis is in the lowest voice. If the CF is the upper voice, only an P8ve or unison may be used at the beginning.
End the counterpoint line (CP) with scale-degree 7 to scale-degree 8 as the CF ends 2 to 1, or vice versa. In minor modes, scale degree 7 must be raised one semitone by the use of an accidental, creating a leading tone at the cadence. For our examples, we will consistently use this standard cadence, referred to as the Clausula Vera to end all counterpoint in minor modes and Mixolydian, but not in the Phrygian mode. The half-step approaching the finalis occurs between scale degrees 2-1 in this mode, with a whole-step between 7-8.
Consecutively repeated notes are seldom used in the CP in Species I and IV, and are generally avoided in Species II and III. This would constitute switching species (two consecutive half notes on the same pitch is either a whole note or a suspension, contrapuntally speaking, and two quarter notes on the same pitch are similarly equivalent to a half note).