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A sign in the Irish language which displays the word Caisleán with initial mutation.
A sign in the Irish language which displays the word Caisleán with initial mutation.

Irish, like all modern Celtic languages, is characterized by its initial consonant mutations.[1] These mutations affect the initial consonant of a word under specific morphological and syntactic conditions. The mutations are an important tool in understanding the relationship between two words and can differentiate various meanings.

Irish, like Manx and colloquial Scottish Gaelic, uses two mutations on consonants: lenition (Irish: séimhiú [ˈʃeː.vʲuː]) and eclipsis (urú [ˈʊ.ɾˠuː]) (the alternative names, aspiration for lenition and nasalisation for eclipsis, are also used, but those terms are misleading).

Originally these mutations were phonologically governed external sandhi effects: lenition was caused by a consonant being between two vowels, and eclipsis when a nasal preceded an obstruent, including at the beginning of a word.

There are also two mutations, t-prothesis and h-prothesis, found on vowel-initial words.

See Irish phonology for a discussion of the symbols used on this page.

Summary table

This table shows the orthographical and phonological effects of both lenition and eclipses, as well as h-prothesis and t-prothesis. In this table a given vowel is represented by ⟨v⟩ and /@/. An prothesised consonant is broad before ⟨a, á, o, ó, u, ú⟩ and slender before ⟨e, é, i, í⟩.

Unmutated Lenition Eclipsis t-prothesis h-prothesis Example


Spell. IPA Example Spell. IPA Ex. Spell. IPA Ex. Spell. IPA Ex. Spell. IPA Ex.
V v /@/ éan


nV n-v /n̪ˠ@/ n-éan


tV t-v /t̪ˠ@/ t-éan


hV hv /h@/ an


/n̠ʲ@/ /tʲ@/
B b /bˠ/ bean


Bh bh /w/ bhean


mB mb /mˠ/ mbean


/bʲ/ /vʲ/ /mʲ/
C c /k/ ceann


Ch ch /x/ cheann


gC gc /ɡ/ gceann


/c/ /ç/ /ɟ/
D d /d̪ˠ/ droim


Dh dh /ɣ/ dhroim


nD nd /n̪ˠ/ ndroim


/dʲ/ /j/ /n̠ʲ/
F f /fˠ/ freagra


Fh fh fhreagra


bhF bhf /w/ bhfreagra


/fʲ/ /vʲ/
G g /ɡ/ glúin


Gh gh /ɣ/ ghlúin


nG ng /ŋ/ nglúin


/ɟ/ /j/ /ɲ/
L l /l̪ˠ/ leanbh


L l /lˠ/ leanbh


/l̠ʲ/ /lʲ/
M m /mˠ/ máthair


Mh mh /w/ mháthair


/mʲ/ /vʲ/
N n /n̪ˠ/ naomh


N n /nˠ/ naomh


/n̠ʲ/ /nʲ/
P p /pˠ/ peann


Ph ph /fˠ/ pheann


bP bp /bˠ/ bpeann


/pʲ/ /fʲ/ /bʲ/
T t /t̪ˠ/ teach


Th th /h/ theach


dT dt /d̪ˠ/ dteach


/tʲ/ /dʲ/
S s /sˠ/ súil


Sh sh shúil


tS ts /t̪ˠ/ tsúil


/ʃ/ /tʲ/

Environments of Lenition

After proclitics

After the definite article

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" e.g. carr an fhir, the man's car (car of the man)
  3. a noun in the dative singular, when the article follows one of the prepositions de "from", do "to" or i "in"
    do + an = don: don fhear "to the man"
    de + an = den: den bhean "from the woman"
    i + an = sa(n): sa chrann "in the tree"; san fhómhar "in the autumn"
an deoch "the drink", although deoch is feminine nominative singular
an tí "of the house", although is masculine genitive singular
an tsúil /ən̪ˠ t̪ˠuːlʲ/ "the eye" (fem. nom. sg.)
an tsaoil /ən̪ˠ t̪ˠiːlʲ/ "of the world" (masc. gen. sg.)

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

After the 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.

In modifier + head constructions

Lenition is blocked in these constructions if two coronals 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

Postposed adjectives in certain circumstances

Environments of Eclipsis

Eclipsis on a sign in Tramore: Fánán na mBád means "slip of the boats." Even in an all-caps inscription, the eclipsis letter is not capitalised.
Eclipsis on a sign in Tramore: Fánán na mBád means "slip of the boats." Even in an all-caps inscription, the eclipsis letter is not capitalised.
Eclipsis on a sign in Raphoe: Sráith na nGael means "Row of the Gaels."
Eclipsis on a sign in Raphoe: Sráith na nGael means "Row of the Gaels."

After plural possessive pronouns

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

Note that a can mean "his", "her" or "their", but these different uses can still be distinguished, since a causes lenition when used as "his" (a bhád), causes eclipsis when used as "their" (a mbád), and neither when used as "her" (a bád).

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-.

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)

After certain preverbal particles

Changes to vowel-initial words

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

However, if neither eclipsis nor lenition is expected, an initial vowel may acquire a prothetic onset consonant. For example, a vowel-initial masculine singular nominative noun requires a t- (a voiceless coronal plosive) after the definite article:

Otherwise, there is the prothetic onset h (a voiceless glottal fricative), which 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.

Examples of h-prothesis


  1. ^ Kevin M. Conroy (April 2008). Celtic initial consonant mutations - nghath and bhfuil? (B.A.). Boston College. Retrieved 4 April 2017.