From the ninth century we started to have knowledge of polyphonic musical practices where the texture increases adding on other sophisticated melodies as a harmonious whole.
However it is possible that these elaborations should come before made such an unwritten instrumental accompaniment and it doesn’t appear in the score.
During the twelfth and thirteenth centuries, the period of the Middle Ages is known as Ars Antiqua and the most frequent ways in which the polyphony is built are the Organum and the Discantus.
We often find two types of Organum:
Parallel Organum is constructed by taking a melody and adding, as the name suggests, another melodic line generally parallel to a distance of perfect fourth, fifth or eighth .
Florid Organum is a little different and is built using notes in long values, often taken from a preexisting melody of Gregorian chant, which is written on one or several tunes, shorter values as if they were melismas, so has also been called melismatic organum.
Discantus breaks the parallelism so that new voices are performed with opposing movements to the lead vocals.
The practice of discant over a cantus firmus marked the beginnings of counterpoint in Western music. From these first motets arose a medieval tradition of secular motets. These were two or three part compositions in which several different texts, sometimes in different vernacular languages, were sung simultaneously over a Latin cantus firmus that once again was usually adapted from a passage of Gregorian chant. It is suspected that, for the sake of intelligibility, in performance the cantus firmus and one or another of the vocal lines were performed on instruments.