Skip to 0 minutes and 5 secondsAfter 1320, the notation system of the so-called period of Ars Nova was enhanced. The most important innovation was that not only the ternary division of musical time was in use, but also a binary division was approved. The organisation of musical time in mensural notation was called mensuration, from mensura, Latin for measuring. The basic concept in that time units are proportional. Let's start with the ratio between longa and brevis, which was called modus. This can be perfect, a ratio of three to one, or imperfect, a ratio of two to one. The same principle can be found on the next lower level, the relation between brevis and semibrevis, which is called tempus. The tempus also can be perfect or imperfect.

Skip to 1 minute and 6 secondsFinally, we find this ratio also between semibrevis and minima, which can also be ternary, named prolatio maior - or binary - in that case the relatio is prolatio minor. This relations between note values visualise different temporal relationships. Together, they provide an effective system of measuring musical time. In the medieval mensuration system, there are four possible combinations of tempus and prolatio. The first is the so-called tempus perfectum cum prolatione minori. As you can see, each brevis is divided in three semibrevis. Each semibrevis is divided in two minimae. We can transcribe it in modern notation using a three-four time. But you have to know that the bar system is totally extrinsic to the medieval mensural system.

Skip to 2 minutes and 22 secondsTranscribing it with the bar system is just a matter of legibility.

Skip to 2 minutes and 30 secondsThe second is the tempus imperfectum cum prolatione maiori. As you can see here, each brevis is divided in two semibrevis. Each semibrevis is divided in three minimae. We can transcribe it in modern notation using a six-eight time. The third is the tempus imperfectum cum prolatione minori. We can transcribe it in modern notation using a two-four bar, or a tempo ordinario, common time. The last is the tempus perfectum cum prolatione maiori. We can transcribe it in modern notation using a nine-eight time. With the four mensuration systems, the range of possible rhythmical features was extended. Metrical variety and compositional diversity was implemented, and complex structures in music were achieved.

What’s new? Perfect and imperfect time

One of the most important changes in the Ars Nova period had been time units, in which musical notes were put into. This process was called mensuration (from mensura, Latin for measuring). Time units were proportional to each other. In this way four different mensuration systems could be achieved.

Find out all about these four systems in this video.

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This video is from the free online course:

From Ink to Sound: Decoding Musical Manuscripts

University of Basel