In Welsh, certain word combinations and grammatical circumstances
can cause the initial letters of some words to change. This is called
mutation. There are three types of mutation - soft, nasal and aspirate.
Together they affect only nine consonants, although not all mutations
affect all nine letters. The unmutated form is called the radical.
To begin with, mutations might seem rather daunting, but if you
practise enough they will soon come naturally. The main thing is
not to worry - you would be undestood even if you missed every mutation.
This cheat sheet goes through the most common circumstances which
cause mutation, but it is not exhaustive. For a definitive guide,
refer to a good grammar book, or the Welsh Academy English-Welsh
soft mutation - treiglad meddal
This mutation (also called lenition) is the most common and
the only one of the three types that is consistently applied across
all Welsh speaking regions. These are the main causes of soft mutation
that you will come accross:
1. Y/yr/r = the, plus a singular feminine noun, but
not a plural feminine noun.
cath = a cat
y gath = the cat
cathod = cats
y cathod = the cats
merch = a girl
y ferch = the girl
merched = girls
y merched = the girls
2. When an adjective follows a feminine singular noun, but
not a plural feminine noun.
cath las = a blue cat
cathod glas = blue cats
merch fach = a little girl
merched bach = little girls
y gath las = the blue cat
y cathod glas = the blue cats
y ferch fach = the little girl
y merched bach = the little girls
When any noun follows an adjective.
hen wraig = an old lady
unig fab = only son
unrhyw fore = any morning
3. When nouns or adjectives follow yn, the linking particle,
(not in). Ll and rh are not affected.
maen drueni = its a pity
maen dda = its good
4. After most monosyllabic prepositions, preposition compounds
(including prepositions with personal endings), and the abbreviated
forms used after i and o.
am, ar, at, dan, dros, (drwy), gan, heb, hyd, i, o, (tan), (tros),
dros ben, o dan, oddi wrth, etc., (but not i mi, i ti, i mewn, i
ith, oi, iw
Trefor - i Drefor = to Trefor
Bangor - o Fangor = from Bangor
blynyddoedd - am flynyddoed = for years
5. After some possesive adjectives.
dy = your (singular)
ei = his
car = a car
dy gar = your car
gafr = a goat
ei afr = his goat
6. After these miscellaneous words, some of which are very
ail = second (in order, not in the time sense)
cyn = as (with equative form)
dau = two (masculine)
dwy = two (feminine)
dacw = there is ...
dyma/ma = here is ...
dyna/na = there is ...
fe or mi = affirmative particle
go = fairly, quite
mor = so (with adjective, but does not affect l or rh)
mor = as (when creating equative form)
neu = or
pa = which
pan = when
pur = very
pwy = which (South)
rhy = too
un = one (feminine)
7. For sentences using inflected verbs:
After the grammatical or notional subject (a word that isnt
the subject, but is in the position of subject) of the sentence.
On intial letter of the verbnoun stem in the affirmative (optional),
interrogative, and negative (when aspirate mutation not applied).
brynu Siân fara? = Did Siân buy bread?
fe welodd Bethan gi = Bethan saw a dog (Bethan is the actual subject
of the sentence)
rhaid i Osian fynd = Osian has to go (Osian is the notional subject
of the sentence)
8. On the initial letter of adverbs of time, saying when
blwyddyn = a year
flwyddyn yn ôl = a year ago
dydd Mercher = Wednesday
ddydd Mercher = on Wednesday
9. In compound words, on the second word.
prif (main) + dinas (city) = prifddinas (capital)
7. After some prefixes.
an + bodlon (willing) = anfodlon (unwilling)
ail + meddwl (think) = ailfeddwl (rethink)
di + defnydd (use) = diddefnydd (useless)
ym + dangos (show) = ymddangos (seem)
nasal mutation - treiglad trwynol
This mutation isnt always spoken, but is always written.
1. After fy = my.
cath = cat
fy nghath = my cat
fy mhlant = my children
Note that sometimes the fy is dropped, so nghath is
sufficient for my cat.
2. After the preposition yn = in, but note that yn also
changes form in some cases.
Caerdydd - yng Nghaerdydd
Penybont - ym Mhenybont
Trefor - yn Nhrefor
Gwent - yng Ngwent
Bangor - ym Mangor
Dolgellau - yn Nolgellau
aspirate mutation - treiglad llaes
Only C always changes in the modern spoken language, with the others
optional, although all three are the norm in writing.
1. After the following miscellaneous words:
a = and
â = with
chwe = six
ei = her (possessive, including iw = to her; oi = of
gyda = with
na = than/or
oni = unil
tri = three (masculine)
tua = about, towards
2. On a negative inflected verb (with personal endings).
colli = lose
cholles i ddim = I didn't lose
talu = pay
thala i ddim = I won't pay
3. Aspiration of vowels.
H is added to words beginning with a vowel after:
ei = her
ein = our
eu = their
E.g.: ei harian = her money
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