Irish declension

In Irish grammar, declension happens to nouns, the definite article, and the adjectives.
Irish mostly has five noun declensions, each with four cases, and singular and plural forms. There are four classes of declension of adjectives in Irish, which correspond to the first four declensions of nouns. There are two genders in Irish, masculine and feminine. The gender of nouns in each declension is somewhat mixed, but there are clear patterns.
The definite article has two forms in Irish: an and na. There is no indefinite article in Irish, so depending on context cat can mean "cat" or "a cat". Their distribution depends on number, case, and gender, and they trigger mutation partly on the basis of the initial sound of the following word.

Nouns

Gender

Nouns in Irish are divided into two genders, masculine and feminine; the Old Irish neuter gender no longer exists. While gender should be learned when the specific noun is learned, there are some guidelines that can be followed:
Generally, nouns in singular form ending with broad consonants are masculine, while those ending in a slender consonant are feminine.
There are some exceptions, mostly dealing with specific endings and suffixes; for example, words ending in / and -ín are categorically masculine, while words ending in are feminine. This leads to some unexpected gender assignments, such as gasóg "boy scout" being feminine, and cailín "girl" masculine.

Case

Irish has four cases: common, vocative, genitive, and the dative or prepositional case.

Nominative

The nominative case is used in the following functions:

Sentence subject
:Tá an cat ag ól. "The cat is drinking."
Sentence object
:Bhris Seán an fhuinneog. "Seán broke the window."
Predicate of the copula is|copula]
:Is amadán é. "He is an idiot."
Object of the prepositions gan "without", go dtí " to" and mar "like, as".
:gan an t-airgead "without the money"
:go dtí an t-am " to the time"
:mar an chearc "like the hen"

Vocative

The vocative case is used in direct address, and is always preceded by the particle a, which triggers lenition. The first declension is the only declension in which the vocative is distinct from the nominative.

→ Cá bhfuil tú, a mhic? "Where are you, son?"
→ A Sheáin, tar anseo! "Seán, come here!"

Genitive

The genitive case indicates possession and material of composition:

→ hata an fhir
→ clann na mná
→ coinnleoirí an easpaig
→ fáinne óir
→ bróga leathair

The object of a verbal noun also requires the genitive:

→ ag caitheamh airgid " spending money"

The object of a compound preposition is in the genitive. Formally, these prepositions are actually prepositional phrases.

→ ar chúl an dorais "behind the door"
→ ar feadh míosa "one month long"
→ ar son na hÉireann "for Ireland's sake"

Dative/Prepositional

The dative/prepositional is used as the object of most simple prepositions except gan and go dtí. In standard language, the dative is almost always identical to the nominative. Some dialects, however, have distinct standalone datives in the second and fifth declensions. In the standard language, only two words Éire and fiche have distinct datives - Éirinn and fichid, respectively. They are also found in certain fixed phrases with nouns of the second declension, such as os cionn.

→ ag an athair "at the father"
→ as an teach "out of the house"
→ ar an arán "on the bread"
→ in oráiste "in an orange"
→ go hifreann "to hell"
→ leis an airgead "with the money"
→ ó Éirinn "from Ireland"

Declension

There are five recognized declensions in Irish. The makeup of the declensions depends on three factors:

the gender of the noun
the formation of the genitive singular
relation of genitive singular to nominative plural

The following chart describes the characteristics of each declension class:

	Nom. sing. ends with:	Gen. sing. ends with:	Gender
First declension	Broad consonant	Slender consonant	Masculine
Second declension	Broad or slender consonant	-e/-í	Feminine with rare exceptions
Third declension	Slender or broad consonant	-a	Masculine or feminine
Fourth declension	Vowel or -ín		Masculine or feminine
Fifth declension	Vowel or slender consonant	Broad consonant	Mostly feminine

First

The first declension is made up of masculine nouns. The nominative singular ends in a broad consonant, which is made slender in the genitive singular. The most common formation of the plural has the opposite pattern: the nominative ends in a slender consonant, the genitive in a broad consonant. The dative is identical to the nominative in both numbers, although an obsolete dative plural in -aibh is still sometimes encountered in old-fashioned literary style.

bád "boat"	Singular	Plural
Nominative	bád	báid
Vocative	a bháid	a bháda
Genitive	báid	bád
Dative	bád	báid

When in the gen. sing. and nom. pl. of a polysyllabic word is made slender, it also becomes voiced, thus:

> >. The resulting is written - and is pronounced,, or, depending on dialect.

marcach "a horseman"	Singular	Plural
Nominative	marcach	marcaigh
Vocative	a mharcaigh	a mharcacha
Genitive	marcaigh	marcach
Dative	marcach	marcaigh

Some nouns undergo a vowel change before the slender consonant of the genitive singular/nominative plural:

ball, baill - an organ, component part
bonn, boinn - a sole, coin
ceann, cinn - a head
fear, fir - a man
iasc, éisc - a fish
mac, mic - a son
poll, poill - a hole

Many words of this declension form the plural with one of the endings -í, -ta, -tha, -anna. These are known as "strong plural" endings, which means the plural is identical in all cases in the standard language. Some examples:

aonach, gen. sg. aonaigh, pl. aontaí - a fair
bealach, gen. sg. bealaigh, pl. bealaí - a way
carr, gen. sg. cairr, pl. carranna - a car
glór, gen. sg. glóir, pl. glórtha - a voice
leanbh, gen. sg. linbh, pl. leanaí - a child
néal, gen. sg. néil, pl. néalta - a cloud
rós, gen. sg. róis, pl. rósanna - a rose
samhradh, gen. sg. samhraidh, pl. samhraí - a summer
scéal, gen. sg. scéil, pl. scéalta - a story
toradh, gen. sg. toraidh, pl. torthaí - fruit

Some nouns have a weak plural in -a:

ceart, gen. sg. cirt, nom. pl. cearta, gen. pl. ceart - a right
cleas, gen. sg. clis, nom. pl. cleasa, gen. pl. cleas - a trick
úll, gen. sg. úill, nom. pl. úlla, gen. pl. úll - an apple

Other strong plural formations are found in:

bóthar, bóthair; bóithre - road
breitheamh, breithimh; breithiúna - judge
briathar, briathair; briathra - verb
cloigeann, cloiginn; cloigne - skull
doras, dorais; doirse - door
ollamh, ollaimh; ollúna - professor
solas, solais; soilse - light

Second

The second declension is made up of mostly feminine nouns, and features a nominative singular form that can end in either a broad or a slender consonant. The genitive singular ends in a slender consonant followed by -e. The most common plural form has a broad consonant followed by -a in the nominative, and a broad consonant alone in the genitive. The vocative has the same endings as the nominative, as does the dative in standard language.

bróg "shoe"	Singular	Plural
Nominative	bróg	bróga
Vocative	a bhróg	a bhróga
Genitive	bróige	bróg
Dative	bróg	bróga

In Connacht Irish and Waterford Irish it is often the case that all nouns of the second declension in the nom. sg. end with a slender consonant.
In some Munster varieties as well as the old literary language, the dative singular is distinct and ends in a slender consonant alone, e.g. i mo bhróig "in my shoe".
When in the gen. sing. is made slender, it is also voiced, so > >. becomes, and is written -í.

girseach "little girl"	Singular	Plural
Nominative/Std. dative	girseach	girseacha
Vocative	a ghirseach	a ghirseacha
Genitive	girsí	girseach
Nonstandard Dative	girsigh	girseachaibh

Many words in this declension form a strong plural with one of the endings -ta,-te, -acha or -eanna:

áit, áite, áiteanna "place"
coill, coille, coillte "forest"
iníon, iníne, iníonacha "daughter"
obair, oibre, oibreacha "work"
spéir, spéire, spéartha "sky"
tír, tíre, tíortha "country"
tonn, toinne, tonnta "wave"
ubh, uibhe, uibheacha "egg"

Other strong plural formations are found in:

fiacail, fiacaile; fiacla - tooth
gualainn, gualainne; guaillí - shoulder
scian, scine; sceana - knife
sliabh, sléibhe; sléibhte - mountain

Third

The third declension is made up of masculine and feminine nouns. It is characterized by the genitive singular in -a. The majority of nouns in this class form the plural in -í. The final consonant of the stem may be broad or slender: it retains its quality in the plural, but is always broad in the genitive singular.

	Singular	Plural
Nominative/Vocative/Dative	broad or slender cons.	-í
Genitive	broad cons. + -a	-í

rás "race"	Singular	Plural
Nominative/Dative	rás	rásaí
Vocative	a rás	a rásaí
Genitive	rása	rásaí

Feminine nouns in -áint or -úint lose their in the gen. sg.; those in -irt have -- instead of -- in the gen. sg.

bagairt, bagartha, bagairtí "threat"
canúint, canúna, canúintí "dialect"

Many words in this declension form the plural with one of the endings -anna or -acha:

am, ama, amanna "time"
anam, anama, anamacha "soul"
droim, droma, dromanna "back"
loch, locha, lochanna "lake"
troid, troda, troideanna "fight, struggle"

Some words in Munster Irish also have a separate dative form:

nom. drom, dat. droim, gen. droma, pl. dromanna "back"

Fourth

The fourth declension is made up of masculine and feminine nouns. It is characterized by a genitive singular that is identical in form to the nominative/vocative/dative singular. The singular may end in a vowel or a consonant. The most common plural ending is -í.

	Singular	Plural
All cases	Vowel or consonant	-í

comhairle " advice"	Singular	Plural
Nominative/Genitive/Dative	comhairle	comhairlí
Vocative	a chomhairle	a chomhairlí

Many words of this declension form the plural with the following endings -tha/-te, -nna or -cha:

ainmhí; ainmhithe "animal"
aturnae; aturnaetha "attorney"
baile; bailte "village"
bus; busanna "bus"
cliamhain; cliamhaineacha "son-in-law"
cneá; cneácha "wound, sore"
cnó; cnónna "nut"
cró; cróite "outhouse; eye of a needle"
dlí; dlíthe "law"
dosaen; dosaenacha "dozen"
ga; gathanna "ray, radius"
gé; géanna "goose"
léine; léine, léinte "shirt"
rá; ráite "saying"
rí; ríthe "king"
sloinne; sloinnte "last name"
teanga; teangacha "language, tongue"
tine; tinte "fire"

Other strong plural formations are found in:

ainm; ainmneacha "name"
airí; airíona "characteristic, symptom"
aithne; aitheanta "commandment"
bruach; bruacha "bank "
cine; ciníocha "race, tribe"
duine; daoine "person, human being"
gabha; gaibhne "blacksmith"
gnó; gnóthaí "business"
oíche; oícheanta "night"

One noun in this class has a weak plural:

bó, bó; ba, bó - cow

Fifth

The fifth declension is made up mostly of feminine nouns and is characterized by a genitive singular that ends in a broad consonant that has been added to the nominative/vocative/dative singular. The most common plural is strong, formed by adding -a to the genitive singular.

	Singular	Plural
Nominative/Vocative/Dative	Vowel or slender consonant	Gen. sg. + -a
Genitive	broad consonant	Gen. sg. + -a

cathair "city"	Singular	Plural
Nominative/Dative	cathair	cathracha
Vocative	a chathair	a chathracha
Genitive	cathrach	cathracha

In some Munster Irish varieties as well as the old literary language, the dative singular is distinct and ends in a slender consonant, for example, do phearsain "to a person", ón gcathraigh "from the city". The word Éire retains the distinct dative form Éirinn in the standard language.
Some words form the genitive singular by changing the final consonant of the nominative singular to broad. The plural is then strong -eacha.

abhainn, abhann, aibhneacha "river"
athair, athar, aithreacha "father"
deartháir, dearthár, deartháireacha "brother"
máthair, máthar, máithreacha "mother"

Other strong plural formations are found in:

bráthair, bráthar; bráithre "brother, friar"
cara, carad; cairde "friend"
namhaid, namhad; naimhde "enemy"
Nollaig, Nollag; Nollaigí "Christmas"

Some nouns have weak plurals; here the genitive singular and genitive plural have the same form:

caora, caorach; caoirigh, caorach - sheep
lacha, lachan; lachain, lachan - duck

Verbal nouns

The most productive verbal nouns end with -adh or -ú. These originally belonged to the third declension, but synchronically are best regarded as separate declensions.
The 1st conjugation verbal noun in -adh has a genitive singular in -te/-ta and a plural in -tí.

briseadh, briste; bristí "breaking"
moladh, molta; moltaí "praising; recommendation"

The 2nd conjugation verbal noun in -ú has a genitive singular in -ithe and a plural in -ithe. These endings are pronounced the same regardless of the spelling distinction.

scrúdú, scrúdaithe; scrúduithe "examining, examination"
síniú, sínithe; sínithe "stretching"

Irregular nouns

The following nouns are declined irregularly:

bean, mná; mná, ban "woman"
deirfiúr, deirféar; deirfiúracha "sister"
deoch, dí; deochanna "drink"
Dia, Dé; déithe "God"
lá, lae; laethanta "day"
leaba, leapa; leapacha "bed"
mí, míosa; míonna "month"
muir, mara; mara "sea"
olann, olla "wool"
talamh, talaimh or talún ; tailte "land"
teach, tí; tithe "house"

Articles

The definite article has two forms in Irish: an and na. Their distribution depends on number, case, and gender, and they trigger mutation partly on the basis of the initial sound of the following word. Each entry of the table gives an example of one noun starting with a consonant and one with a vowel.
Dative is used with all prepositions in Ulster usage; in Munster and the standard language it is used only with den "from the", don "to the", and sa "in the" but there are also Munster dialects in which only sa triggers lenition and den and don eclipse, as with every other article-preposition compound. In Connacht sa eclipses whereas den and don lenite. Dative is used outside Ulster with other prepositions.
The article never mutates a following or in the singular, and is lenited to rather than the usual. furthermore lenites in both dative and in the singular with feminine nouns but does not lenite at all with masculine nouns.
It does, however, eclipse and in Munster dialects and forms like "ag an ndoras" instead of the usual pattern "ag an doras", which is used in all other dialects, do occur.
There is no indefinite article in Irish, so depending on context cat can mean "cat" or "a cat".

Adjectives

Almost all adjectives in Irish can be used either predicatively or attributively. A predicative adjective is one that forms a part of the predicate, like red in the sentence The car is red. An attributive adjective directly modifies a noun, as in the red car.
A predicate adjective in Irish does not inflect:

Tá an fear sin beag. "That man is small."
Tá na fir sin beag. "Those men are small."
Tá an bhean seo beag. "This woman is small."
Tá na mná seo beag. "These women are small."

A predicate adjective expressing a value judgment is often preceded by the particle go. This particle attaches to a following vowel.

Tá mé go maith. "I'm fine"
Tá an scéal go holc. "The story is bad."
Bhí an aimsir go hálainn. "The weather was beautiful."

In Ulster, go is not generally used in these cases.
An attributive adjective mostly follows the noun and is inflected:

an fear beag "the small man"
an fhir bhig "of the small man"

There are four classes of declension of adjectives in Irish, which correspond to the first four declensions of nouns:

	Nom. sg. ends with:	Gen. sg. masc. ends with:	Gen. sg. fem. ends with:
1st decl.	broad cons.	slender consonant	slender consonant + -e
2nd decl.	slender cons.	slender consonant	slender consonant + -e
3rd decl.	slender cons.	slender consonant	broad consonant + -a
4th decl.	vowel	= nom. sg.	= nom. sg.

First declension

bacach "lame"	Masc. sg.	Fem. sg.	Plural
Nominative	bacach	bhacach	bacacha
Genitive	bhacaigh	bacaí	bacach

Third declension

cóir "just"	Masc. Sg.	Fem. Sg.	Plural
Nominative	cóir	chóir	córa
Genitive	chóir	córa	cóir, córa

Fourth declension

This declension does not inflect, but it does mutate.

crua "hard"	Masc. sg.	Fem. sg.	Plural
Nominative	crua	chrua	crua
Genitive	chrua	crua	crua

Irregular adjectives

;Notes

The nominative plural undergoes lenition only if the noun ends with a slender consonant: cait bhacacha "lame cats". Otherwise, the adjective in the nominative plural does not lenite: táilliúirí bacacha "lame tailors".
The long form of the genitive plural is used when the noun has a strong plural, e.g. máithreacha bacacha "of lame mothers". The short form is used when the noun has a weak plural, e.g. cat bacach "of lame cats".
The dative has the same form as the nominative.
The vocative has the same form as the nominative except in the masculine singular of the 1st/2nd declension, where it has the same form as the genitive.

Comparative

Irish adjectives have a comparative form equivalent to the comparative and superlative in English. The comparative does not undergo inflexion and is the same as the feminine singular genitive in regular and many irregular adjectives.

Syntax of comparison

There are two constructions to express the comparative:
1) Copula + comparative form + subject + ná + predicate. The preterite of the copula causes lenition, while the present tense does not.

Ba thréine Cáit ná Cathal. "Cáit was stronger than Cathal."
Is airde Seán ná mise. "Seán is bigger than me."
B'óige an madra ná an cat. "The dog was younger than the cat."
Is fearr Gaeilge bhriste ná Béarla cliste. "Broken Irish is better than clever English."

2) níos/ní ba/ní b’ + comparative + ná + predicate. Níos is used if the sentence is in the present or future tense.
Ní ba/ní b’, which triggers lenition, is used if the sentence is in the past tense. Ní b’ is used before words starting with vowels and ní ba before those starting with consonants.

Tá an ghrian níos gile ná an ghealach. "The sun is brighter than the moon."
Beidh Peadar níos saibhre ná a athair. "Peadar will be richer than his father."
D'éirigh Peadar ní ba shaibhre ná a athair. "Peadar became richer than his father."
Bhí Seán ní b’airde ná mise. "Seán was bigger than me."

A superlative is expressed as a relative clause: noun + is/ba/ab + comparative form.

an cailín is tréine "the strongest girl"
an cailín ba thréine "the strongest girl"
an buachaill is óige "the youngest boy"
an buachaill ab óige "the youngest boy"