Appendix:Irish Mutations
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Appendix:Irish Mutations

Irish, like all modern Celtic languages, is characterized by its initial consonant mutations. These mutations affect the initial consonant of a word depending on morphological and syntactic conditions. The mutations are an important tool in understanding the relationship between two words and can differentiate meaning.

Irish uses two mutations on consonants: lenition and eclipsis. There are also three mutations--eclipsis, t-prothesis, and h-prothesis--found on vowel-initial words.

The unmutated form (the "base" form) is known as the radical.

Words subject to mutation

Not all words are subject to mutation. The only types of words subject to mutation are:

  • Nouns
  • Verbs
  • Adjectives (rarely subject to eclipsis outside fixed expressions)
  • Third-person disjunctive pronouns (é, í, ea, and iad)

All other words (adverbs, determiners, prepositions, etc.) are not subject to mutation.

Words that trigger mutation in specific instances always come immediately before the words that mutate, and apart from nouns, almost all words that trigger mutation in general have to be repeated for each one. When words that trigger mutation (including nouns) do not have to be repeated for each one (e.g. idir... agus... ("both... and..."), mar ("like, as"), series of adjectives (or nouns in the genitive) after a given noun), mutation is not blocked by intervening words: idir fhir agus mh ("both men and women"), mar dharacha agus mhailpeanna ("like oaks and maples"), cait mhóra dhubha ("big black cats"), etc. Note that idir does not trigger lenition when it means "between": idir fómhar agus geimhreadh ("between autumn and winter"), idir tithe ("between houses"), etc.


Effects of lenition

Consonants change as follows when they undergo lenition:

Radical Lenited
b /b?/, /b?/ bh /w/, /v?/
c /k/, /c/ ch /x/, /ç/
d /d/, /d?/ dh /?/, /j/
f /f?/, /f?/ fh (silent)
g /?/, /?/ gh /?/, /j/
m /m?/, /m?/ mh /w/, /v?/
p /p?/, /p?/ ph /f?/, /f?/
s /s?/, /?/ sh /h/
Note: sc, sm, sp, and st do not mutate.
t /t/, /t?/ th /h/

Other consonants do not change under lenition.

Environments of lenition

After proclitics

After the definite article an and contractions of it with prepositions, e.g. don, ón

The definite article triggers lenition of:

  1. a feminine noun in the nominative singular
    an bhean ("the woman")
  2. a masculine noun in the genitive singular
    an fhir ("of the man")
  3. a noun in the dative singular, when the article follows one of the contractions den ("from the"), don ("to the") or sa ("in the") (san before a vowel sound) (note: in some dialects, lenition occurs also after other preposition + article combinations):
    don fhear ("to the man")
    den bhean ("from the woman")
    sa chrann ("in the tree"); san fhómhar ("in the autumn")
  • d and t are never lenited after the article:
an deoch ("the drink"), although deoch is feminine nominative singular
sa teach ("in the house"), although teach follows sa
  • Where s would be lenited after the article, it becomes ts /t, t?/ (rather than sh /h/):
an tsúil ("the eye") /?n tu:l?/ (fem. nom. sg.)
ón tsráid ("from the street") /o:n t:d?/ (fem. dat. sg.)
an tsaoil ("of the world") /?n ti:l?/ (masc. gen. sg.)
  • In some dialects, this same change happens after any n and l in a leniting environment:
an-tsásta ("very happy") (standard an-sásta)
scoil tsaothair ("industrial school") (standard scoil saothair)
After the vocative particle a
After possessive pronouns

The possessive pronouns that trigger lenition are mo ("my"), do ("your (sg.)"), a ("his")

After certain prepositions
After the preterite/conditional of the copula is
  • Ba dhuine mór é. ("He was a big person.")
  • Ba dheas uait é. ("That was nice of you.")
After preterite preverbal particles
After certain preverbal particles
A verb in the preterite, imperfect or conditional

These were originally preceded by the particle do and often still are in Munster.

  • bhris ("I broke")
  • bhrisinn ("I used to break")
  • bhrisfinn ("I would break")

In modifier + head constructions

Lenition is blocked in these constructions if two coronals other than r (i.e. d, l, n, s, t) are adjacent.

After certain numbers

The singular form is used after numbers and is lenited in the following cases:

After preposed adjectives

Constructions of adjective + noun are written as compounds.

After most prefixes
The second part of a compound

In head + modifier constructions

In these constructions coronals are lenited even following other coronals.

Genitive nouns in certain circumstances
  • aimsir bháistí "rainy weather" (lenition after a feminine singular noun)
  • buidéil shú "bottles of juice" (lenition after a plural ending in a slender consonant)
  • teach Sheáin "Seán's house" (lenition of a definite noun in the genitive)
Postposed adjectives in certain circumstances
  • bean dheas "a pretty woman" (lenition after a feminine singular noun)
  • na fir mhóra "the big men" (lenition after a plural noun ending in a slender consonant)
  • ainm an fhir bhig "the name of the small man" (lenition after a masculine singular noun in the genitive)
  • sa chrann mhór "in the big tree" (lenition after a noun lenited by virtue of being in the dative after den, don, or sa(n))


Effects of eclipsis

A sign in Ireland showing a lower-case b before a capital P in an eclipsing environment.

1. Consonants change as follows when they undergo eclipsis. When eclipsed words are capitalized, it is the consonant of the radical that is capitalized, while the letter(s) showing eclipses remain small.

Radical Eclipsed Capitalized radical Capitalized eclipsed
b /b?/, /b?/ mb /m?/, /m?/ B mB
c /k/, /c/ gc /?/, /?/ C gC
d /d/, /d?/ nd /n/, /n?/ D nD
f /f?/, /f?/ bhf /w/, /v?/ F bhF
g /?/, /?/ ng /?/, /?/ G nG
p /p?/, /p?/ bp /b?/, /b?/ P bP
t /t/, /t?/ dt /d/, /d?/ T dT

The other consonants do not change under eclipsis.

2. A vowel receives a preceding n- (pronounced /n/ before a, o, u, /n?/ before e, i). The hyphen is not used before a capital letter.

Radical Eclipsed Capitalized radical Capitalized eclipsed
a, á n-a, n-á A, Á nA,
e, é n-e, n-é E, É nE,
i, í n-i, n-í I, Í nI,
o, ó n-o, n-ó O, Ó nO,
u, ú n-u, n-ú U, Ú nU,

Environments of eclipsis

After plural possessive pronouns

The possessive pronouns that trigger eclipsis are ár ("our"), bhur ("your (pl.)"), a ("their")

After certain numbers

The numbers that trigger eclipsis (the noun being in the singular) are:

After the preposition i ("in")

Before a vowel in is written instead of i n-, though before the spelling reforms of the mid-20th century this was not the case.

Genitive plural nouns after the definite article

The genitive plural article na eclipses a following noun:

Dative singular nouns after the definite article

In western and southern dialects, nouns beginning with a noncoronal consonant are eclipsed after combinations of preposition + article in the singular (except den, don, and sa(n), which trigger lenition):

A vowel-initial word is not affected after the definite article an.

After certain preverbal particles

  • an poll a dtagann na coiníní as "the hole that the rabbits come out of"
  • An dtagann sé gach lá? "Does he come every day?"
  • bhfuil mo spéaclaí? "Where are my glasses?"
  • Dúirt sé go dtiocfadh sé. "He said that he would come."
  • mbeadh a fhios sin agam "if I had known that"

A vowel-initial word is not affected after the interrogative particle an.

Changes to vowel-initial words

Vowel-initial words undergo eclipsis, as explained above, except after an.

A vowel-initial word does not change where lenition is expected:

  • an oíche "the night" (feminine singular nominative noun after definite article)
  • an uisce "of the water" (masculine singular genitive noun after definite article)
  • ó Albain "from Scotland" (noun after leniting preposition)
  • seanathair "grandfather" (noun after preposed adjective: sean "old" + athair "father")

But where neither eclipsis nor lenition is expected, an initial vowel may acquire a prothetic t- or h- onset consonant.


A vowel-initial masculine singular nominative noun takes the prothetic onset t- after the definite article. The hyphen is not used before a capital letter:

  • an t-uisce "the water" (masculine singular nominative)
  • an tÉireannach "the Irishman" (masculine singular nominative)

T-prothesis is also found with vowel-initial numerals (attributive or ordinal) after the article in the nominative singular with both masculine and feminine nouns:

  • an t-aon bhád ("the one boat")
  • an t-ochtú bó ("the eighth cow")
  • an t-aonú lá fichead ("the twenty-first day")


The prothetic onset h- comes only when both the following conditions are met:

  1. a proclitic causes neither lenition nor eclipsis of consonants
  2. a proclitic itself ends in a vowel sound

There is no need for adding a hyphen before a lowercase letter as with t-prothesis as h does not occur initially in native Irish words outside prothesis.

Examples of h-prothesis

Colloquially in some dialects, verbs beginning with a vowel undergo h-prothesis in the past indicative autonomous form; there is no triggering proclitic in this case:

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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