Strict and free style in polyphony
Polyphony is a type of polyphony, based on the combination and simultaneous development of two or more independent melodies. In polyphony, in the process of its development, two styles were formed and developed: strict and free. Strict style or strict letter in polyphony. Strict style was improved in vocal and choral music of the XV-XVI centuries (although the polyphony itself, of course, originated much earlier).