Counterpoint describes a kind of music where melodic phrases play on top of each other, causing notes to work against other notes. The term comes from 'point against point', where a 'point' would be a note of some kind. A note moves against another note when the interval between the two notes grows or shrinks. Chords may (and often do) develop from this technique, but are incidental; this kind of music focuses on individual melodies working together. The composer Johann Sebastian Bach always wrote music using counterpoint.
Generally, such music created from the Baroque period on might be described as counterpoint, while such music created prior to Baroque times would be called polyphony. Hence, the composer Josquin Des Prez always wrote polyphonic music.
Homophony, by contrast, features music where chords or intervals play out the melody without working the notes against each other. Most popular music written today use homophony as a dominant feature within the music.
Johann Fux published Gradus ad Parnassum, a work published in 1725 intended to help teach students how to write counterpoint. In this, he describes five species.
In first species counterpoint, a note simply works against another note. The two notes are played simultaneously, and move against each other, also simultaneously. The species is said to be expanded if one of the notes is broken up (but repeated).
In second species counterpoint, two notes work against a longer note. The species is said to be expanded if one of the shorter notes varies in length from the other.
In third species counterpoint, three notes move against a longer note. As with second species, it is expanded if one of the shorter notes vary in length from another.
In fourth species counterpoint, a note is held while changing note move against the holding note, creating a dissonance, followed by the holding note changing to create a subsequent consonance as the changing note holds. Fourth species counterpoint is said to be expanded when the notes vary in length from each other. The technique requires holding a note across the beat, creating syncopation.
In fifth species counterpoint, sometimes called "florid counterpoint", the other four species of counterpoint are combined within the melody.
(page originally created by Fleeb)