The Commemoratio Brevis de Tonis et Psalmis Modulandis was written around 900AD and
contains an important exposition on the rhythm of Latin chant which instructs that the
precise ratio of long to short be observed in all chant (which would include hymns like Deus
creator omnium, Guido's 'metric song' like the hymn Rex aeterne Domine and 'quasi
prosaic song' such as responsories, etc).
Commemoratio Brevis de Tonis et Psalmis Modulandis, ed Hans Schmid, p176
The above passage explicitly refers to equalities of duration between shorts and longs and
advocates measured durations for all chant. Such a practice would be much at odds with
much current performance practice of chant in Western Europe. As sung generally today,
lines of Gregorian chant alternate but little between longs and shorts. It is doubtful that
such a lecture on how to sing the psalms in Latin would be heard in many modern choir
rehearsals. Relying on square notation, most pitches are standardly given a single short
duration, against the evidence of the earliest rhythmic notations of plainchant (which divide
signs into sets of long and shorts) and the theoretical writings of the same period. This
equalist rhythm can often be subtly 'nuanced' after the manner of Dom Pothier's 'oratorical'
So do not let inequality of singing mar the
sacred songs; not for moments let any
neume or note be improperly prolonged
or shortened; nor, through lack of care in
a song, eg, a responsory etc, let it be
started to be dragged out more sluggishly
than at first.
Breves must not be more expended as is
meet for longs; nor should longs slip by in
slippery uneveness more hastily as is
meet for shorts.
Just as all longs are equally long, let the
shortness of shorts be equal except at the
ends of lines, which must likewise be
observed carefully in a song. Let all which
are long run together with those which are
not long by proper numerical durations,
and any song must be gone through
entirely at the same hold of speed from
end to end ...
and in accordance with the durations of
length, let there be formed short moments,
so that they be neither greater nor lesser,
but always one twice as long as the other.
This evenness of singing is called rhythm
by the Greeks and number by the Latins
for, assuredly, all song should be
diligently measured after the manner of
poetic metre. Masters of schools should
studiously impress this on those learning
and, from the start, they should instruct in
the same discipline of equity or rhythm
and, during the singing, teach about
number through the beating of feet or
hands or something else as you wish, so
that, from practice in youth, they will
understand the difference between
evenness and unevenness and not get
used to worse habits.
Inaequalitas ergo cantionis cantica
sacra non viciet; non per momenta neuma
quaelibet aut sonus indecenter
protendatur aut contrahatur; non per
incuriam in uno cantu, verbi gratia
responsorii vel caeterorum, segnius
quam prius protrahi incipiatur.
Item brevia quaeque impendiosiora non
sint, quam conveniat longis, nec longa
inaequalitate lubrica festinantius
labantur, quam conveniat brevibus.
Verum omnia longa aequaliter longa,
brevium sit par brevitas exceptis
distinctionibus, quae simili cautela in
cantu observandae sunt. Omnia, quae
diu, ad ea, quae non diu, legitimis inter
se morulis numerose concurrant et
cantus quilibet totus eodem celeritatis
tenore a fine usque ad finem peragatur ...
et secundum moras longitudinis momenta
formentur brevia, ut nec maiore nec
minore, sed semper unum alterum duplo
Quae canendi aequitas rithmus Grece,
Latine dicitur numerus, quo certe omne
melos more metri diligenter
mensurandum sit. Hanc magistri scolarum
studiose inculcare discentibus debent et
ab initio infantes eadem aequalitatis sive
numerositatis disciplina informare et
inter cantandum aliqua pedum
manuumve vel qualibet alia percussione
numerum instruere, ut a primaevo usu
aequalium et inaequalium distantia
calleant nec peiore usu assuescant.