Leonin made use of the descant, adding to the chant basis. Hildegard composed some unusual material, some quite inventive, leaving scholars uncertain as to how exactly to interpret it. Polyphony seems to have been there in some compositions. Later polyphonists added more "voices," and even gimells, where one "voice" becomes two, and extreme voice ranges, calling for vocalists with skills far beyond what a local group could handle. This was much later; the 16th century seeing a flowering of this kind of choral work.
The singing became so demanding and expensive, with choristers trained to soloist level, and with an expensive master composer and director, that Pope Marcellus among others called for a halt. He said something to the effect that the music was too complex to be understood by the listener, and unsingable by the average choir. Nevertheless, it makes for an amazingly beautiful tapestry of sound when sung by experts such as the Tallis Scholars and The Sixteen, among others.