Mensural notation
Notation of polyphonic music from the late thirteenth to the early seventeenth century.
What it means
Mensural notation is the notation system of polyphonic music from the late thirteenth to the early seventeenth century. Its innovation compared with the older neume notation lies in the name: it measures duration. While neumes record above all pitch and direction of movement and leave duration to performance, mensural notation fixes a particular value for every sign — the precondition for several independent voices to be brought together.
In the notation
From largest to smallest the values are called maxima, longa, brevis, semibrevis, minima, and, below that, still smaller levels. In the older form the noteheads are filled in (black notation), from the mid-fifteenth century onward mostly open (white notation), probably because paper increasingly replaced parchment as writing material. How the values relate to one another is stated by the mensuration sign: the division can be twofold or threefold, separately for each level. Barlines are absent. Several notes of one syllable are grouped into ligatures, whose shape at the same time indicates the values; a punctus can lengthen or organize.
Musical use
On this foundation the entire polyphonic repertoire arose, from the Ars antiqua to the vocal polyphony of the Renaissance. It has usually survived not in scores but in choirbooks or partbooks, in which each voice stands on its own. With the seventeenth century, the consistently twofold division, the barline, and score arrangement became established; the semibrevis became today's whole note, the mensuration signs became the time signature.
An early form was described and codified around 1280 by Franco of Cologne in his treatise Ars cantus mensurabilis. The French Ars nova of the fourteenth century expanded the system with smaller values and with prolation, the division of the semibrevis into minims.
Performance practice
For music-making, a modern transcription is the right path; the original is worthwhile alongside it as a check. With transcriptions, take care that added barlines suggest an accentual order that the music does not actually have — the organization results from the text and the voice leading. Practise, therefore, phrasing across the barlines and take your bearings from the cadences rather than from the bar strokes.