ABSTRACT
To judge by scholarly reiteration from Coussemaker to the present day, it seems that few have found cause to question the definition of resfacta as written composition and of cantare super librum as improvisation on a given tenor. The "important difference" between resfacta and cantare super librum is that the parts of resfacta are "mutually obliged" with respect to the law and ordering of consonances, while the minimum requirement for cantare super librum is that each voice be consonant with the tenor, not needing to be subject to other voices. In sum, resfacta is composition, usually but not necessarily written, a completed piece resulting from application of, and choices between, the rules of counterpoint. Cantare super librum is the singing of counterpoint, following strict rules of interval combinations in relation to a tenor and, with experience and skill, to other pre-existing parts as well.
