Organum

As early as the 9th century a practice of singing in parallel fourths and fifths began and was called organum. Several types developed that were variously named. They all had the common characteristic of using a preexisting chant (vox principalis), to which was added one or more melodic lines.

Parallel organum added a second voice (vox organalis), fixed at the interval of a fifth or fourth below the vox principalis. Free organum employed contrary and oblique motion in the vox organalis, whereas a later type, melismatic organum, used elaborate decorative note groups in the vox organalis against the very slow-moving values of the vox principalis.

All styles of organum emphasized the use of the perfect intervals of the unison, fourth, fifth, and octave at cadential points.