Counterpoint

A counterpoint is the relationship between two or more melody lines that are played at the same time. These melodies are dependent on each other to create good-sounding harmonies, but also are independent in rhythm and contour.

The melody lines are called voices, and a piece of music can have counterpoint between two, three, four, or more voices. An example of counterpoint in two voices is Bach’s “Invention 8 in F Major”, one of his most famous piano pieces:

The most important thing to note is that each voice has to be its own melody first and foremost. For example, in four-part counterpoint you can’t have three melodies and then one extra harmonic line, or it would be considered an extended three-part counterpoint.

Melody comes first when writing a piece of counterpoint, and each individual voice has to work independently as a melody and not just as a harmony to a different voice. In counterpoint, the intervals you most want between notes in different melody lines are:

3rds and 6ths. These are nice sounding intervals, and you can have many of these in a row.
The second most popular intervals, especially at the beginning and end of a piece, are 5ths and octaves. These are more stable intervals, so they also sound nice, but they’re a bit boring so using them too much is usually frowned upon.

Motion is the term used to describe how a melody changes notes. In counterpoint there can be parallel, similar, contrary, or oblique motion between two melodic lines. Some rules for a Counterpoint are:

The final note of all melody lines (the cantus firmus and the counterpoint melody) must be approached by a step (either a major or minor second interval).
If there is a skip (any interval greater than a step) in one direction - either ascending or descending - it should be followed by a step in the other direction.
Another rule is that there must be a high point in the counterpoint melody (the one that’s not the cantus firmus), approximately in the middle of the melody.
There should not be multiple 5ths played in a row, what is called parallel 5ths, or consecutive 5ths. That means if you have an interval of a 5th (C to G, for example) between the two melodies, then the next notes can’t make an interval of a 5th. The same rule applies to both octaves and 4ths.

Basically, if you have an octave, 5th, or 4th, you can’t use parallel motion from those intervals. Parallel 3rds and 6ths are very often seen, however, and even encouraged.

Canons are good examples of counterpoints. They are pieces in which we hear an initial melody, which is then imitated by one or more other parts. This imitation might be an exact replica of the original melody, or it might be altered in some way.

Usually, the imitations are identical to the original voice, so essentially it is the same melody being sung by multiple parts, starting at different times. Each voice or group of voices begins singing two bars after the previous entry and thus the ultimate effect can be very impressive. For example: