Audio: fourth species counterpoint (0:09)
fourth species counterpoint sings fourth species counterpoint in the key of F lydian. The fourth species counterpoint figure shows the fixed melody in the upper part of the score and the contrapuntal melody in the lower part.
Fourth species counterpoint extends the theme of dissonance to cover suspension. It extends the rhythm to include syncopation.
A suspension occurs when one note is delayed and overlaps another. In fourth species counterpoint, the interval on the first beat may be consonant or dissonant while that on the second is consonant.
A consonance may resolve up or down to another consonance, a dissonance must always resolve by step down to a consonance. This resolution of a dissonance is always by step down, not step up, regardless of whether the other melody is ascending or descending in pitch. It seems strange to prohibit resolution by step up but that is just the way it is.
Another little foible of fourth species counterpoint is that a seventh cannot resolve to an octave. A seventh should always resolve down to a sixth, not up to an octave. The reason given for this prohibition is custom, nobody composed that way in the olden days. This prohibition is illogical, and is acknowledged as such, since the inverse of a seventh, the second, can resolve down to unison.
In situations when a dissonance cannot be resolved, the options are to write a consonance instead, revert to an earlier species or use an untied note.
Fourth species counterpoint is an offset variant of first species counterpoint. A quick way to write fourth species counterpoint is to write it in first species then offset one of the melodies forward half a bar.