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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 ['?e:.v?u:]) and eclipsis (urú ['?.u:]) (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.

Lenition (séimhiú)

Effects of séimhiú

  1. A stop becomes a fricative. Voicing is retained, as is place of articulation except with the coronals.
    • /p?/ -> /f?/
    • /p?/ -> /f?/
    • /t/ -> /h?/
    • /t?/ -> /h/
    • /k/ -> /x/
    • /c/ -> /ç/
    • /b?/ -> /w/, /v/
    • /b?/ -> /v?/
    • /d/ -> /?/
    • /d?/ -> /j/
    • /?/ -> /?/
    • /?/ -> /j/
  2. /m?/ becomes /w/ or /v/; /m?/ becomes /v?/.
  3. /s?/ and /?/ become /h/; but /s?p(?)/, /s?m(?)/, /s?t/, /?t?/, /s?k/, and /?c/ do not mutate.
  4. /f?/ and /f?/ are deleted.

Séimhiú is symbolized in the orthography by an h following the consonant in question or, in some older typefaces and texts, by a dot () above the letter that has undergone lenition.

Lenition in Irish
Normal Séimhiú Gloss
peann /p?a:n/ pheann /f?a:n/ "pen"
teach /t?ax/ theach /hax/ "house"
ceann /ca:n/ cheann /ça:n/ "head"
bean /b?an/ bhean /v?an/ "woman"
droim /d?i:m?/ dhroim /i:m?/ "back"
glúin /u:n?/ ghlúin /u:n?/ "knee"
máthair /m?a:h/ mháthair /wa:h/, /va:h/ "mother"
súil /s?u:l?/ shúil /hu:l?/ "eye"
freagra /fa?/ fhreagra /a?/ "answer"

The other consonants do not change under lenition.

Environments of séimhiú

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"
  • /d, d?/ and /t, t?/ are never lenited after the article:
an deoch "the drink", although deoch is feminine nominative singular
an tí "of the house", although is masculine genitive singular
  • Where an /s?, ?/ would be lenited after the article, it becomes /t, t?/ (rather than /h/), written ts:
an tsúil /?n tu:l?/ "the eye" (fem. nom. sg.)
an tsaoil /?n ti:l?/ "of the world" (masc. gen. sg.)
After the vocative particle a
  • a Bhríd "Bríd!"
  • a Sheáin "Seán!"
  • a chairde "my friends!"
After possessive pronouns

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

  • mo mhac "my son"
  • do theach "your house"
  • a pheann "his pen"
After certain prepositions
  • de chrann "out of a tree"
  • faoi chrann "under a tree"
  • mar dhuine "as a person"
  • ó Chorcaigh "from Cork"
  • roimh mhaidin "before morning"
  • trí shioc agus shneachta "through frost and snow"
  • um Cháisc "at Easter"
  • idir fhir agus mh "both men and women"
  • ar bhord "on a table"
After the preterite/conditional of the copula
  • Ba dhuine mór é. "He was a big person."
  • Ba dheas uait é. "That was nice of you."
After the preterite preverbal particles
  • Níor mhúinteoir é. "He was not a teacher."
  • Níor thug mé "I didn't give"
  • Ar shagart é? "Was he a priest?"
  • Ar tháinig sé? "Did he come?"
After certain preverbal particles
  • thuigim "I don't understand"
  • thagann sé "if he comes"
  • an fear a thabharfaidh dom é "the man who will give it to me"
A verb in the preterite, imperfect or conditional

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

  • bhris mé "I broke"
  • bhrisinn "I used to break"
  • bhrisfinn "I would break"

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:

  • aon bhó amháin "one cow"
  • an chéad bhliain "the first year"
  • dhá theach "two houses"
  • beirt fhear "two men"
  • trí bhád "three boats"
  • ceithre bhó "four cows"
  • cúig phunt "five pounds"
  • mhí "six months"
After preposed adjectives

Constructions of adjective + noun are written as compounds.

  • seanbhean "old woman"
  • drochdhuine "bad person"
  • dea-sheirbhís "good deed"
  • nuatheanga "modern language"
  • tréanmhuir "stormy sea"
  • fíorchneas "true skin"
  • ardbh "high pressure"
  • ógfhear "young man"
After most prefixes
  • an-bheag "very small"
  • ró-bheag "too small"
  • aisghabháil "retake"
  • athbhliain "new year"
  • dobhréagnaithe "undeniable"
  • fochupán "saucer"
  • forbhríste "overalls"
  • idirchreidmheach "interconfessional"
  • ilphósadh "polygamy"
  • leasmháthair "stepmother"
  • shásta "unhappy"
  • neamhchodladh "insomnia"
  • príomhchathair "capital city"
  • sobhriste "fragile"
The second part of a compound
  • ainmfhocal "noun" (lit. "name word")
  • ghorm "dark blue"
  • státfhiach "national debt"

In head + modifier constructions

In these constructions coronals are lenited even following other

  • 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))

Eclipsis (urú)

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.

Effects of urú

The following tables show how eclipsis affects the start of words. Eclipsis is symbolised in the orthography by adding a letter--or occasionally two letters--to the start of the word. If the word is to be capitalised, the original first letter is capitalised, not the letter or letters added for eclipsis. An example is the "F" in Ireland's national anthem, Amhrán na bhFiann.

1. A voiceless stop or /f?, f?/ is voiced:

Sound change Normal Urú Gloss
/p?/ -> /b?/ práta /pa:t/ bpráta /ba:t/ "potato"
/p?/ -> /b?/ peann /p?a:n/ bpeann /b?a:n/ "pen"
/t/ -> /d/ tráta /t?a:t/ dtráta /d?a:t/ "tomato"
/t?/ -> /d?/ teanga /t?a/ dteanga /d?a/ "tongue"
/k/ -> /?/ cat /kat/ gcat /gat/ "cat"
/c/ -> /?/ ceann /ca:n/ gceann /?a:n/ "head"
/f?/ -> /w/, /v/ focal /fk?l?/ bhfocal /vk?l?/ "word"
/f?/ -> /v?/ freagra /fa?/ bhfreagra /va?/ "answer"

In the West Muskerry dialect, /s?/ and /?/ are also voiced, but this is not reflected in the orthography nor is it standardised outside of that barony.[]

2. A voiced stop becomes a nasal:

Sound change Normal Urú Gloss
/b?/ -> /m?/ bainne /b?a:n/ mbainne /m?a:n/ "milk"
/b?/ -> /m?/ bean /b?an/ mbean /m?an/ "woman"
/d/ -> /n/ droim /d?i:m?/ ndroim /n?i:m?/ "back"
/d?/ -> /n?/ dinnéar /dn?e:/ ndinnéar /nn?e:/ "dinner"
/?/ -> /?/ glúin /u:n?/ nglúin /u:n?/ "knee"
/?/ -> /?/ geata /?at/ ngeata /?at/ "gate"

3. A vowel receives a preceding /n/ or /n?/ (broad preceding a/o/u, slender preceding e/i). However, a vowel-initial word is not affected after the definite article an.

Sound change Normal Urú Gloss
/e/ -> /n?e/ éan /e:n/ n-éan /n?e:n/ "bird"
/i/ -> /ni/ oíche /i:h?/ n-oíche /ni:h?/ "night"

The other consonants do not change under urú.

Environments of urú

After plural possessive pronouns

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

  • ár gcairde "our friends"
  • bhur bpáistí "your (pl.) children"
  • a mbád "their boat",

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:

  • seacht gcapall "seven horses"
  • ocht n-asal "eight donkeys"
  • naoi gcat "nine cats"
  • deich bpeann "ten pens"

After the preposition i "in"

Before a vowel in is written instead of i n-.

  • i dteach "in a house"
  • in Éirinn "in Ireland"

Genitive plural nouns after the definite article

The genitive plural article na eclipses a following noun:

  • na n-asal "of the donkeys"
  • na bhfocal "of the words"

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)

  • ag an bhfear "by the man"
  • ar an gcrann "on the tree"

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"

Changes to vowel-initial words

A vowel-initial word does not change if a séimhiú 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")

However, if neither urú nor séimhiú is expected, an initial vowel may acquire a prothetic onset consonant. For example, a vowel-initial masculine singular nominative noun requires a t- after the definite article:

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

Otherwise, there is the prothetic onset h, 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

  • a haois "her age" (after possessive pronoun a "her"; compare with a aois, "his age" and a n-aois, "their age" with regular urú)
  • go hÉirinn "to Ireland" (after preposition go "to, towards")
  • le hAntaine "with Antaine" (after preposition le "with")
  • na hoíche "of the night" (on feminine singular genitive noun after definite article)
  • na héin "the birds" (on plural nominative/dative noun after definite article)
  • chomh hard le caisleán "as high as a castle" (after chomh [xo] "as")
  • go hálainn "beautifully" (after adverb-forming particle go)
  • himigh uaim "Don't leave me!" (after negative imperative particle "don't")
  • an dara háit "the second place" (after an ordinal numeral)


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

  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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