Final answer:
A polyphonic composition based on one main theme is called a fugue. It is characterized by the orderly entrance of various voices, each presenting and imitating the main theme, creating interwoven melodic lines that form a harmonious overall theme.
Step-by-step explanation:
A type of polyphonic composition based on one main theme is known as a fugue. Polyphony is a musical texture consisting of two or more independent melodic voices. This contrasts with monophony, which uses a single melody without harmonic support. The fugue is one of the most complex types of polyphonic music. It starts with a single voice presenting the main theme or subject, which is subsequently imitated by other voices entering in succession, each voice adding to the evolving texture of the piece. This style became particularly prevalent during the Renaissance and reached its peak in the Baroque period through the works of composers such as Johann Sebastian Bach.
Polyphony played a significant role in the transition from Medieval music to Renaissance music, marking a shift from the monophonic liturgical music like Gregorian chant to the complex interweaving lines of polyphonic music. The fugue exemplifies how multiple melodies can coexist and interact, producing a harmonious and intricately connected overall theme.