In the 10th century, music was starting to diverge from unison; one voice maintained a somewhat slow and steady tune (called the tenor) and another voice waxed ecstatic (often called the superius or the altus). Although the rhythms in the wandering voice didn’t matter much to the steady voice, there were certain markers that needed to be met so that syllables or unison notes could be lined up.
Without written notation, both singers had to listen and take visual cues from one another to stay in step. There was the tenor voice plodding purposefully toward the final note while the other voice wiggled and wandered and all but mamboed in a way that thrilled the listener.
They had to come up with some way to keep together, to change syllables at the same moment and to come to a satisfying end together. At first, they must have employed significant glances or nods, but in time, a form of rhythm evolved. The original two-part music, organum and conductus, was performed as the monks walked down the aisle as part of the mass ceremony. A natural rhythm accompanies such things, and voila! Rhythm joined melody.
At first, rhythms were only allowed in certain prescribed forms, what are known as the rhythmic modes. They do seem to travel in threes—the count tallies to three or multiples of three in each of them. This may have had some religious symbolism, but it is actually more likely to come from secular music. The dancing aspect of the rhythms is rather easy to hear.
The work being done to create a notation system was pivotal in the development of rhythmic modes. There had to be some way to aurally tie one voice to the other, and writing it down made it easier both to learn and to perform. It also made it possible for more than two singers to participate.
It is thought that the development of rhythmic modes originates from the treatise De musica by St. Augustine in the 4th and 5th centuries. He described two units of measure, a long (longa) and a short (brevis), where the short was exactly half the length of a long. But they didn’t really get down to documenting these until they had block-note mensuration in the late 11th century. The first notation for the rhythmic modes was based on the block-notes they used for writing down the chants.
It isn’t known who originated the six rhythmic forms, although it is rather likely to have begun at the school at Notre Dame in Paris, where considerable work was being done regarding documenting music theory and coming up with new musical forms. In the 13th century, there was a definitive treatise (attributed to Johannes de Garlandia) that at last described these modes in De musica mensurabili positio.
The first mode was likely the first to be used, a pattern of a longer note and then a shorter one. The reversal of the order to a short and then a long note was a natural progression, and that is the second mode. It is thought that the sixth mode was a sort of ornamentation of this arrangement in that it is three short notes, equaling both the first and second mode in duration.
The third, fourth and fifth modes are thought to be later developments. The third consists of three notes, one that is half-again as long as a long note (or the equivalent of three shorts), a short, and then a normal-length long (like a dotted quarter, an eighth, and a quarter note in modern notation). The fourth mode is a short, a long, and a triple-wide long (like an eighth, a quarter and a dotted quarter note in modern notation). And the fifth mode is like two triple-wide longs (two dotted quarter notes in modern notation).
At first, the problem must have been that re-using the same rhythmic patterns throughout a single piece grew tedious and it was also a little hard to document—not everything ends neatly at the end of a rhythmic mode. By the 13th century, scholars at Notre Dame had come up with something called fractio modi (the breaking of the mode), which combined notes of several modes and filled in spaces with notes that didn’t comply with any mode and with rests (silence). They also created a diamond-shaped note to indicate running patterns, usually downward and which may have been performed as ornaments rather than staying in a particular rhythm. (This shape got borrowed back into block-note chant notation.)
Polyphony (multiple melodic lines) made it necessary to indicate how the various voices fit together. The Notre Dame School replaced the even unmeasured flow of plainchant and early polyphony with the recurrent patterns of long and short notes of the rhythmic modes. No song is likely to have maintained any single rhythmic pattern for the duration—it would have seriously squelched the exuberant nature of the wandering voice or voices.
And of course, a sensitive artist wouldn’t follow the notation on the page with mathematical rigor, but would introduce rhythmic nuance suggested by the text and the mood of the poem and by the melody itself. This probably caused the creation of even more developments in the musical world.
It’s interesting to note that the six rhythmic modes correspond to the “feet” of meters in classical poetry. Although the modes have names (Trochaic, Iambic, Dactylic, Anapestic, Spondaic, and Tribrachic), they are usually referred to by their numbers (1-6).
Like the literary meters, the formulas created by these rhythmic modes allowed development into the musical shapes we find familiar today—soon, they needed meters divisible by 2 or 4, and now, we have things with sevens and fives and nines!
Next in the series, non-European modes.
Early Medieval Music Up to 1300, edited by Dom Anselm Hughes, Oxford University Press, London, 1954
Medieval Music, Richard H. Hoppin, W. W. Norton & Company, New York, 1978
A History of Western Music (8th edition), J. Peter Burkholder, Donald Jay Grout, Claude V. Palisca, W. W. Norton & Company, New York, 2010