Stated simply, polyphony has four main tenets:
Two or more non-unison lines or “voices.”
Each line shares the same key signature, but otherwise, they remain independent.
There is melodic equality between each line. Polyphony does not feature a central melody with accompaniment.
Polyphonic lines can but do not necessarily illuminate an underlying or hidden harmonic structure.
Scholars and composers have long argued about the definition of true polyphony, with some experts calling certain polyphonic compositions “disguised homophony.” One of the earliest forms of polyphony is called organum. Throughout history, polyphony has been a skill that composers have cultivated in varying degrees. Polyphony can range from passages that are very dense to passages that are quite clear. Polyphony becomes even more complex when you consider modern usage, especially the work of György Ligeti whose music is sometimes labeled micropolyphony.
Some compositions also fall into the category of heterophony. In heterophony, you vary or ornament the same melodic line. True polyphonic music features multiple, independent lines.
Polyphony is similar to another term, counterpoint. But historically, the latter suggests a hierarchy of lines, while the former implies pure linear equality. Due to the independence built into polyphonic lines, the rhythms differ too. However, you may see lines mirroring or copying one another in some staggered fashion. Just beware: If your lines resemble one another too closely, you're probably writing heterophony.
FIGURE 9-3: Musical example of two-voice polyphony
As a beginning composer, you may find limited use for true polyphony. By default, most contemporary music features a central melody with accompaniment. This is simply the norm in the modern era. However, it's a good idea to experiment with equal, independent voices in your compositions. This will develop a more acute sense of melody. If anything, you will learn how to create more imaginative and complementary modal patterns. It could also be a way to introduce various themes in a novel, creative manner. Figure 9-3 shows a simple example of two-voice polyphony using tenor and baritone voices.