The transition from organum to discant was effected about the year 1100.
It is interesting to recall the origin of our words “treble” and “discant.”
To hear him discant you would have thought his wings were sprouting.
Res est blanda canor; discant cantare puell—Singing is a charming accomplishment: let girls learn to sing.
Then the spirit moving her, she began to discant on things past and people vanished.