Counterpoint/First species counterpoint

First species counterpoint is the most simple of counterpoints existent. First species counterpoint consists only of a cantus firmus and a line located above or below the cantus firmus, called the counterpoint. As a result, first species counterpoint is also referred to as one-against-one or 1:1 counterpoint due to 1 note of cantus firmus being played while 1 other note of the counterpoint is being played. These notes are often seen as quarter notes, half notes or whole notes, though any particular combination of notes is acceptable.

There are two main points to go over. First, there is the individual lines themselves and their individual rules. Next, we will go over how the notes should be intertwined together.

Motions
In counterpoint, motion is the movement in which two notes move in relation to each other. There are four types of motions. Contrary motion or oblique motion must be used when moving a note to a perfect consonance. When progressing to an imperfect consonance, any motion may be used.
 * 1) Contrary motion: The motion of the two notes in two opposite directions
 * 2) Oblique motion: The motion of one note while the other does not move
 * 1) Similar motion: The motion of both notes in which they move the same direction
 * 2) Parallel motion: The motion of both notes in which they move in the same direction in the same interval

Consonance and dissonance
A consonance is an interval between two notes in counterpoint, whether they be between to consecutive notes(also called leaps) or the cantus firmus in relativity to the counterpoint. There are two types of consonance.

A dissonance, contrary to a consonance, is an interval that may be considered unpleasant to the ear. This includes major and minor seconds, major and minor sevenths, tritones and augmented and diminished intervals. These should not be seen at all in first species counterpoint.
 * A perfect consonance is a consonance that may not be major, minor, augmented or diminished, but instead a perfect interval. This includes an perfect fifth, octave, or union
 * Note that perfect fourths are not included in this list. Perfect fourths in traditional and stricter counterpoint is considered dissonant in two-voice counterpoint. In less strict counterpoint, however, fourths are considered to be consonant.
 * An imperfect consonance is a consonance that includes most major and minor intervals(but not all). These may include a major or minor third or a major or minor sixth.

Leaps
Leaps are two consecutive notes in either the cantus firmus or the counterpoint. Here are some guidelines and rules that should be followed.
 * Do not use two perfect consonances in leaps. It is also recommended to not to not two perfect consonances twice in a row in general.
 * It is recommended to not have three successive leaps of the same size.
 * Large leaps in general should be avoided(exceptions are occasionally seen, however, such as 10ths)
 * Leaps greater than a third should be responded with a change in melodic direction

Range and length
A melody in counterpoint should be only up to ten measures. The range should not exceed two measures.

Beginning and endings
When writing counterpoint above the cantus firmus, notes should begin on do or sol. When writing counterpoint below the cantus firmus, notes should only begin on do due to sol creating a perfect fourth, which is considered dissonant or imperfect.

The final note of a counterpoint should always be do and a perfect octave above or below the cantus firms.

Resolving notes
In counterpoint, certain notes on in the counterpoint line should generally resolve to another note. The leading tone, or Ti, should resolve to do.