Irish initial mutations

1. A stop becomes a fricative. Voicing is retained, as is place of articulation except with the coronals.
   • /pˠ/ → /fˠ/
   • /pʲ/ → /fʲ/
   • /t̪ˠ/ → /hʲ/
   • /tʲ/ → /h/
   • /k/ → /x/
   • /c/ → /ç/
   • /bˠ/ → /w/, /v/
   • /bʲ/ → /vʲ/
   • /d̪ˠ/ → /ɣ/
   • /dʲ/ → /j/
   • /ɡ/ → /ɣ/
   • /ɟ/ → /j/
2. /mˠ/ becomes /w/ or /v/; /mʲ/ becomes /vʲ/.
3. /sˠ/ and /ʃ/ become /h/; but /sˠp(ʲ)/, /sˠm(ʲ)/, /sˠt̪ˠ/, /ʃtʲ/, /sˠk/, and /ʃc/ do not mutate.
4. /fˠ/ and /fʲ/ 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.

The other consonants do not change under lenition.

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"

• /d̪ˠ, dʲ/ and /t̪ˠ, tʲ/ are never lenited after the article:

an deoch "the drink", although deoch is feminine nominative singular

an tí "of the house", although tí is masculine genitive singular

• Where an /sˠ, ʃ/ would be lenited after the article, it becomes /t̪ˠ, tʲ/ (rather than /h/), written ts:

an tsúil /ən̪ˠ t̪ˠuːlʲ/ "the eye" (fem. nom. sg.)

an tsaoil /ən̪ˠ t̪ˠiːlʲ/ "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 mhná "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

• ní thuigim "I don't understand"
• má 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"

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"
• sé 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"
• ardbhrú "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"
• míshásta "unhappy"
• neamhchodladh "insomnia"
• príomhchathair "capital city"
• sobhriste "fragile"

The second part of a compound

• ainmfhocal "noun" (lit. "name word")
• dúghorm "dark blue"
• státfhiach "national debt"

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))

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 /fˠ, fʲ/ is voiced:

In the West Muskerry dialect, /sˠ/ and /ʃ/ 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:

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

The other consonants do not change under urú.

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).

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"

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

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

The genitive plural article na eclipses a following noun:

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

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"

• 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?"
• Cá bhfuil mo spéaclaí? "Where are my glasses?"
• Dúirt sé go dtiocfadh sé. "He said that he would come."
• dá mbeadh a fhios sin agam "if I had known that"