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'I' and 'O' : a Compositional
Basis
Cyweirdant a Thyniad
The music was unlike other North European
art music of the time, since it was not an unaccompanied
melodic line; like plainsong, not a melody sounding against
a drone; like much medieval bagpipe music, not a line of
melody accompanied by an instrumental line or texture; like
the troubadours' songs and not different lines of melody
sounding together; like a polyphonic mass or a madrigal.
This music (cerdd dant) was composed according to a binary
system in which the eight notes or strings of the octave
were divided into two sets: principal and weak, prinsipal
a gwan. A typical division might be:
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 ,
C, D,
G (principal)
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A,.Bb,
Eb, F
(weak)
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corresponding closely to Boethius'
'fixed' and 'movable' strings (De institutione musica,
written before 510 A.D.) and the 'hestotes' and
'kinoumenoi' of the ancient Greeks. The principal or fixed
set is identified with the Pythagorean ratio - 12 : 9 : 8 :
6. Applied to the division of the monochord, this ratio
gives rise to the octave, fifth, fourth and the wide,
Pythagorean tone.
In cerdd dant a stave or line of
music is divided into equal periods of time and each period
is assigned either to the cyweirdannau ('I's) or
tyniadau ('O's). 'O's are usually made from the
lleddfdannau, the movable strings or notes which do
not correspond to the 12 : 9 : 8 : 6 set. The 'I's and 'O's
are arranged into binary patterns, The Twenty Four Measures
of String Music, Y Pedwar Mesur ar Hugain Cerdd
Dant.
Page 107, Robert ap Huw MS,
transcribed by Robert Evans
(107)
llyma / r / pedwar mesur arhigain kerdd
dant
Here are the twenty four measures of
string music.
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mak y mwn hir
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IIII OOOO IOIO IIII OOOO IOII
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korffiniwr
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IIOOIOII . IIOOIOII
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korsgoleff
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IIOIIOOIOII
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Rhiniart
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IOOI . IOOII
[sic] [ r.
IOOII . IOOII ]
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koraldan
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IIIOIOOIOOOI
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tresi heli
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IOOOIIIOOOIOII
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wnsach
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IIIIOOOI
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kor dia
tutlach
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IOIIOOOIIOOIIII
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korfinfaen
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IOIIOII . IOIIOII
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korwrgog
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IOOIOIIOII
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karsi
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IOOOIOII . IOOOIOII
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brath yn ysgol
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IOIIOIOOIOIIOIOOIOII
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fflamgwr gwran
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IOII . IOIIOOIIOOII
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mak y mwn byrr
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IIOOIIII
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kalchan
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IIOOIIIIOI
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bryt odidog
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OOIO : OOIO : IIOI : IIOI
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trwsgwl mawr
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OOOOIIIIOOOOIOII
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tytyr bach
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OOIIOOII
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mak y mynfaen
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OO)IIOO : OOIIOOIIII
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toddf
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OIIOOOII
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hatyr
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OOIOII . OOIOII
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mak y delgi
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OIIIOII
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alban hyfaidd
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IOII . OIOO . OIOO . IOII
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alfarch
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OOOOOOOO IIIIIIII
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terfyn y pedwar mesur arhigain kerdd
dant
End of the twenty four measures of
string music.
By permission of the British
Library, Robert ap Huw, MUSICA, Additional
14905.
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Page 107, Robert ap Huw MS,
showing the names of the mesurau or measures
and the mesurau in binary
notation.
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During a 'I' the cyweirdannau are
predominant and during an 'O' or tyniad, the
lleddfdannau are predominant. Generally the 'I's and
'O's are easy to discern in the bass part of the tablature.
In the treble especially, notes or strings from the
non-predominant set are recruited to make musical
figuration. The bass is generally more stable than the
treble. The figuration is not mere ornamentation. There are
four main categories of figure each with one or more
rhetorical functions.
By permission of the British
Library, Robert ap Huw, MUSICA, Additional
14905.
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Detail of p. 35, Robert ap Huw
MS, showing part of the key for reading the
tablature. The names of the figures are written
first, then the figures are represented as columns
of letters with different signs above them, as they
appear in the tablature. The fingering and damping
for each figure is shown in triangular notation on
a stave. Robert ap Huw has used the free space at
the end of the line to write a fingering chart for
the lower hand.
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Plethiadau,
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in English, 'plaitings' or
'weavings', these may begin a cyweirdant
('I') or tyniad ('O'), may beautify between
a 'I' or an 'O' and cause contention, each with the
other.
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Tagiadau,
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'chokings', these are stops or
rests between 'I's and 'O's.
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Cysylltiadau,
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'joinings' or 'connections',
these join 'I's and 'O's.
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Crychiadau,
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'wrinklings' or 'ripples'
(tremulando effects), these complete or perfect
'I's and 'O's or come between 'I's and
'O's.
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