In fact, these manuscripts embody different stylistic developments of the Magnus Liber itself, particularly in the field of composition mentioned by Anonymous IV, the clausula.

[5] It is unknown whether the Magnus Liber had one sole contributor, though it is noted by scholars that large parts were composed by Léonin (1135–c.1200) and this conclusion is drawn from the writings of Anonymous IV.

While the concept of combining voices in harmony to enrich plainsong chant was not new, there lacked the established and codified musical theory techniques to enable the rational construction of such pieces.

The Magnus Liber represents a step in the development of Western music between plainchant and the intricate polyphony of the later thirteenth and fourteenth centuries (see Machaut and Ars Nova).

In the organi of the Magnus Liber, one voice sang the notes of the Gregorian chant elongated to enormous length called the tenor (from Latin 'to hold'), but was also known as the vox principalis.

The practice of keeping a slow moving "tenor" line continued into secular music, and the words of the original chant survived in some cases as well.

The extant manuscripts provide a number of notational challenges for modern editors since they contain only the polyphonic sections to which the monophonic chant must be added.