Irish has five noun declensions, each with four cases (nominative, vocative, genitive, dative), and singular and plural forms. Noun endings are typified by broad and slender consonants, and vowels; case endings are characterised by the broadening and slenderising of consonants, and the addition of suffixes.
Plurals are categorised as weak if the genitive plural is the same as the nominative singular; and strong if the genitive plural is the same as the nominative plural. Weak plurals are formed by slenderising consonants, or adding the suffix ‑a. Strong plural suffixes include ‑aí, ‑anna, ‑ta and ‑acha, and a few nouns in -a/e with syncopation. The dative plural ‑aibh is non-standard, and considered archaic/dialectical.
The vocative has the same form as the nominative in the second to fifth declensions. In the first declension, it is slender in the singular and broad + a in the plural.
There are two genders in Irish, masculine and feminine. The gender of nouns in each declension is somewhat mixed, but there are clear patterns.
Quick reference tableEdit
|Gender||m||f ||m  & f ||m & f ||f & m |
|‑il, ‑in, ‑ir;|
|Gen||slender||+ e ||+ a||-||broad;|
vowel + ch, d, n
|Dat||-||slender ||-||-||slender gen|
|Weak Plural ||Nom||slender;
|+ a ||+ a ||+ a |||
|Voc||+ a||+ a||+ a||+ a|
|Dat ||+ aibh||+ aibh||+ aibh||+ aibh|
The defining feature of each declension is the genitive singular. By this definition, a few nouns defy classification, notably:
The Caighdeán lists deoch and teach as irregular, but just a little digging shows them to be second declension nouns.
Multiple declension nounsEdit
Some Irish nouns belong to more than one declension. There is a distinction to be made between historical/dialectical declension variants of a particular noun, and homonyms. A good example of the latter is eas (“waterfall”) from Old Irish es, and eas (“stoat”) from Old Irish nes.
The following is not meant as an exhaustive list.
|araí||f, appearance||f, bridle|
|cruicéad||m (teanglann)||m (wiki)||cricket|
|dún||m, str||m, wk||fort|
|eas||m, str, waterfall
m, wk, stoat
|méid||f, size||m, amount|
|ráth||m, str, fort
f, str, shoal
m, wk, guarantor
|ros||m, linseed||m, wooded headland|
|úr||m, freshness||m, heath|
- ^ Verbal nouns per se can be considered a class of their own; verbal nouns as substantive fall into the canonical classes
- ^ The accusative has the same form as the nominative, and together they are sometimes called "common"
- ^ Traces of PIE dual forms still exist, especially after dhá, and with the second declension nouns bos, bróg, cluas, cos and lámh
- ^ In the jargon, velarised and palatised
- ^ By this definition, a few nouns defy classification, notably bean, deirfiúr, Dia, lá, leaba, mí
- ^ Notably, 2nd and 5th
- Rarely, the slender version in ‑e; e.g., súil, npl. súile
- ^ Slender versions are ‑í, ‑eanna, ‑te, ‑eacha; ‑ta/te may be aspirated to ‑tha/the
- ^ Certain nouns and noun endings are associated with particular plurals, see Irish Nouns
- ^ e.g. briathar, pl briathra, bráthair, pl bráithre
- cf. Latin -ibus. Considered archaic/dialtectical. If *busannaibh were a form, it could be interpreted as (omni)bus‑anna‑ibus
- ^ e.g. all first declension nouns are masculine
- ^ Initial mutations are not discussed further here. Wikitionary declension templates include bare and initial-mutated forms, in the context of the article
- ^ There are three masculine nouns in the 2nd declension: im, sliabh, teach
- ^ Especially suffixes -éir, -óir, úir (cf. Latin -or)
- ^ Especially suffix ‑acht/‑aíocht; verbal nouns as substantive in ‑áil, ‑irt, ‑úint
- ^ Abstract nouns ending in a vowel
- ^ Male familial nouns, and the ordinals 20-90
- ^ Masculine, except for girls' names, e.g, Máirín
- ^ In this table, "-" means that the form is the same as the nominative singular
- ^ In this table "+" means that the preceding consonant should be broadened or slenderised, if necessary, to agree with the suffix. In this particular case (+ e), a broad consonant is slenderised
- ^ Genitive singular in í comes from nouns in ‑(e)ach: í < ighe
- ^ Formally, the genitive singular without the suffix -e
- ^ Strong-plural cases all have the same form
- ^ There are relatively few weak plurals in the third declension
- ^ There is only a couple of weak plurals in the fourth declension
- ^ There are some irregular plurals in the 5th declension, with genitive plural = genitive singular
- ^ An exception to the "weak plural" rule; e.g., súil, gpl. súl
- ^ Originally dearbh + siúr
- ^ Actually a verbal noun, where leapa < leabtha
- ^ Almost regular fifth declenstion, except that the radical ending, -úr, is broad