Irish, like all modern Celtic languages, is characterized by itsinitial 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 andeclipsis. There are also three mutations—eclipsis,t-prothesis, andh-prothesis—found on vowel-initial words.
The unmutated form (the "base" form) is known as theradical.
Not all words are subject to mutation. The only types of words subject to mutation are:
All other words (adverbs, determiners, prepositions, etc.) are not subject to mutation.
Words that trigger mutation always come immediately before the words they modify, and apart from nouns, almost all such words have to be repeated for each word (thusdo bhuachaillí agusdo chaillíní(“to boys and girls”) butcaitmhóradhubha(“big black cats”)). There are several exceptions, however, such asidir...agus...(“between/both...and...”) andmar(“like, as”), thusidirfhir agusmhná(“both/between men and women”),mardharacha agusmhailpeanna(“like oaks and maples”).
Consonants change as follows when they undergo lenition:
| Radical | Lenited |
|---|---|
| b/bˠ/,/bʲ/ | bh/w/~/vˠ/,/vʲ/ |
| c/k/,/c/ | ch/x/,/ç/ |
| d/d̪ˠ/,/dʲ/ | dh/ɣ/,/j/ |
| f/fˠ/,/fʲ/ | fh ∅ |
| g/ɡ/,/ɟ/ | gh/ɣ/,/j/ |
| m/mˠ/,/mʲ/ | mh/w/~/vˠ/,/vʲ/ |
| p/pˠ/,/pʲ/ | ph/fˠ/,/fʲ/ |
| s/sˠ/,/ʃ/ | sh/h/ |
| t/t̪ˠ/,/tʲ/ | th/h/ |
Note:sc,sf,sm,sp, andst do not mutate and other consonants do not change under lenition.
After the definite articlean and contractions of it with prepositions, e.g.don,ón:
The definite article triggers lenition of:
After the vocative particlea
After possessive determiners
The possessive determiners that trigger lenition aremo(“my”),do(“your (sg.)”),a(“his”)
After certain prepositions
After the preterite/conditional of the copulais, except in Northern Irish when the word starts witht,d and optionallys:
After preterite preverbal particles
After certain preverbal particles
A verb in the preterite, imperfect or conditional
These were originally preceded by the particledo and often still are in Munster.
Lenition is blocked in these constructions if two coronals other thanr (i.e.d,l,n,s,t) are adjacent.
After certain numbers
When the singular form is used after numbers, it is lenited in the following cases. Always withaon "one" anddhá "two" (dá with the article:an dá); note thatd(h)á is followed by the dual. The other numbers, 3 to 6, do not cause lenition when followed by the plural.
Note that there is a subtle semantic difference between the use of the singular and plural, that of group unit, e.g.trí chearc "three chickens (as one lot)", or not as a unit, e.g.trí cearca "three chickens not as part of a single group".
After preposed adjectives
Constructions of adjective + noun are written as compounds.
After most prefixes
The second part of a compound
In these constructions coronals are lenited even following other coronals.
Genitive nouns in certain circumstances
Postposed adjectives in certain circumstances
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/bˠ/,/bʲ/ | mb/mˠ/,/mʲ/ | B | mB |
| c/k/,/c/ | gc/ɡ/,/ɟ/ | C | gC |
| d/d̪ˠ/,/dʲ/ | nd/n̪ˠ/,/nʲ/ | D | nD |
| f/fˠ/,/fʲ/ | bhf/w/,/vʲ/ | F | bhF |
| g/ɡ/,/ɟ/ | ng/ŋ/,/ɲ/ | G | nG |
| p/pˠ/,/pʲ/ | bp/bˠ/,/bʲ/ | P | bP |
| t/t̪ˠ/,/tʲ/ | dt/d̪ˠ/,/dʲ/ | T | dT |
The other consonants do not change under eclipsis.
2. A vowel receives a precedingn- (pronounced/n̪ˠ/ beforea,o,u,/nʲ/ beforee,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,nÁ |
| e,é | n-e,n-é | E,É | nE,nÉ |
| i,í | n-i,n-í | I,Í | nI,nÍ |
| o,ó | n-o,n-ó | O,Ó | nO,nÓ |
| u,ú | n-u,n-ú | U,Ú | nU,nÚ |
The possessive determiners that trigger eclipsis areár(“our”),bhur(“your (pl.)”),a(“their”)
The numbers that trigger eclipsis (the noun being in the singular) are:
Before a vowelin is written instead ofi n-, though before the spelling reforms of the mid-20th century this was not the case.
The genitive plural articlena eclipses a following noun:
In western dialects, nouns beginning with a noncoronal consonant are eclipsed after combinations of preposition + article in the singular (exceptden,don, andsa(n), which trigger lenition). In southern dialects,t andd are also affected, and optionallys:
A vowel-initial word is not affected after the definite articlean.
A vowel-initial word is not affected after the interrogative particlean.
Vowel-initial words undergo eclipsis, as explained above, except afteran.
A vowel-initial word does not change where lenition is expected:
But where neither eclipsis nor lenition is expected, an initial vowel may acquire a prothetict- orh- onset consonant.
A vowel-initial masculine singular nominative noun takes the prothetic onsett- after the definite article. The hyphen is not used before a capital letter:
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:
The prothetic onseth- comes only when both the following conditions are met:
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 ofh-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: