Musical parts

A part (or voice) generally refers to a single strand or melody of music within a larger ensemble or a polyphonic musical composition. There are several senses in which the word is often used:

Part-writing (or voice leading) is the composition of parts in consideration of harmony and counterpoint. In the context of polyphonic composition the term voice may be used instead of part to denote a single melodic line or textural layer. The term is generic, and is not meant to imply that the line should necessarily be vocal in character, instead referring to instrumentation, the function of the line within the counterpoint structure, or simply to register.

The historical development of polyphony and part-writing is a central thread through European music history. The earliest notated pieces of music in Europe were gregorian chant melodies. It appears that the Codex Calixtinus (12th century) contains the earliest extant decipherable part music. Many histories of music trace the development of new rules for dissonances, and shifting stylistic possibilities for relationships between parts.

In some places and time periods, part-writing has been systematized as a set of counterpoint rules taught to musicians as part of their early education. One notable example is Johann Fux's Gradus ad Parnassum, which dictates a style of counterpoint writing that resembles the work of the famous Renaissance composer Palestrina. The standard for most Western music theory in the twentieth century is generalized from the work of Classical composers in the common practice period. For example, a recent general music textbook states,

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