Fischer, Pieter. 1968. The theory of music from the Carolingian era up to 1400. RISM Series B: Bibliographies of materials organized by topic.  München: G. Henle Verlag.

Reaney, Gilbert. 1963. Modes in the Fourteenth Century, in Particular in the Music of Guillaume de Machaut. Organicae voces: Festschrift Joseph Smits von Waesberghe, edited by Pieter Fischer, 137-143. Amsterdam: Institute for Medieval Music.