The symbolism of chant rhythm

In surviving treatises, recommendation is made only that pitches be sung using pitch
durations which relate to each other by a 2:1 ratio in accordance with custom as ancient as
the pagan Greeks.  There is no unequivocal reference containing any advice contrary to
St Augustine clearly indicates that St Ambrose's hymn in iambic metre, Deus creator
was sung to such a ratio, and that what Guido calls 'metricos cantus' (exemplified by
St Bede in the Ambrosian hymn O Rex aeterne Domine) was also sung to the same ratio.  
Remigius mentions the ratio, the Scolica enchiriadis gives clear instruction on singing an
office antiphon to the same ratio while the
Commemoratio brevis clearly connects the ratio
with all chant, warning firmly against durational inequalities as does
Elias Salomonis. The
ancient commentators on Guido's
Micrologus such as Aribo round off by confirming the
universality of ratio in chant rhythm through describing the morula and using antiphons,
responsories and gradual psalms to illustrate counted proportions, and
de Grocheo opposes
the notion that plainchant is 'in no way measured'.

Terms such as 'ratio', 'aequalitas', 'numerositas', 'simplus', 'duplus', 'plaudo' and 'percussio'
pepper centuries of descriptive discourse very unlike in quality to 20th century descriptions
of the nature of Gregorian chant rhythm.  Instead, the sources present an ethic of rhythmic
balance and order which reflected believed practical and spiritual realities.

In book IV of
De Trinitate, St Augustine links the 2:1 ratio to redemption itself.  He regards
the ratio as of divine institution and very vigorous within the human being, citing singing in
octaves as an easily audible expression of it.  The
Commemoratio brevis in turn has a clear
perception of God ordaining the creation of beauty through equality and number.

Commemoratio Brevis de Tonis et Psalmis Modulandis, ed Hans Schmid, p175-176
Gregorian Rhythm in the Gregorian Centuries, Dom Gregory Murray, 1957

A full reading of the sources should leave the unbiased reader with little doubt about the
rhythmic inclinations of the ancient masters who wrote about Gregorian chant during the first
millenium and beyond.  On the one hand, they were great proponents of measured note
quantities and, on the other, they make no clear reference to rhythmic nuancing except to
speak against it.  As the earliest chant manuscripts do not clearly indicate the exact
durational values represented by neumes, a history of the rhythm of Gregorian chant can
thus be envisaged as being traditionally, even divinely, proportional in nature from its very
beginning until the Romantic era innovations of the monks of Solesmes.
academic treatment
Caution should be observed above all that
the chant is performed with diligent equality;
otherwise, if this be absent, it is deprived of
its essential character and defrauded of its
legitimate perfection. Without this (equality)
the choir is set in confusion by the
discordant ensemble; neither can anyone
join in harmoniously with others nor sing
artistically by himself. In equity manifestly
has God the creator appointed all beauty to
consist, nor less that which the ear than that
which the eye perceives; for he has ordered
all things in measure, weight and number.
De cetero ante omnia sollicitus
observandum, ut aequalitate diligenti
cantilena promatur, qua utique si  
careat, praecipuo suo privatur iure et
legitima perfectione fraudatur. Sine hac
quippe chorus concentu confunditur
dissono nec cum aliis concorditer
quilibet cantare potest nec solus docte.
Aequitate plane pulchritudinem omnem,
nec minus quae auditu quam quae visu
percipitur, Deus auctor constare
instituit, qui in mensura et pondere et
numero cuncta disposuit.
The symbolism of chant rhythm
The morula
The tenor and the pausa
The tenor
The distinction
Commemoratio brevis
Scolica enchiriadis
Academic treatment
De Grocheo
Musica enchiriadis
Alcuin, Remigius & Guido
Metric chant
Tempus antiquorum
Poetic metre
Unmetered poetry