Plurals in the Irish language nouns have no definite rules. Hope this helps!

I jest. Firstly, banish your English language comparisons from your mind. This isn’t the place for “But in English we do XYZ,” “but I need to know the rules!”. Secondly, you have to realise, Irish is not like English or any other major European language, as there’s really no codified form that won out.

While there are no definite rules, there are some hints as to what the plural of a noun may be so let us continue.

Let’s recall that there are five recognised noun declensions in Irish, each with four cases (nominative, vocative, genitive, dative) as well as singular and plural forms.

A declension is a grouping of nouns that tend to form the plural and genitive according to a common pattern. Nouns can have strong or weak plurals.

Strong vs Weak Plurals

• If a noun is the same form in the nominative and genitive plural (e.g. dánta > dánta, oifigí > oifigí, cluichí > cluichí), it is considered a strong plural.
• If a noun has different forms in the nominative and genitive plural (e.g. focail > focal, fuinneoga > fuinneog), it is called a weak plural.
• The genitive plural form of weak plurals is the same as the nominative singular (Except for a few irregular nouns that don’t belong to a declension).

What about dialectal variations?

Ah yes! Plural forms can also vary based on the dialect being spoken – we’re looking at you Conamara – and some words simply have multiple acceptable plural forms. Let’s take the word áit (place). Sometimes in Conamara you’ll hear áiteanna, sometimes áiteachaí. Sometimes both versions in the same sentence from the same speaker!

Even English has this problem – there’s no reason why the plural of mouse should be mice but house becomes houses. You just have to learn which plural goes with which word.

I’ll be summarising declensions below but be honest, you can still bypass all of this by simply using foclóir.ie or teanglann.ie to see the endings if you’re confused.

The Nominative Singular and Plural of nouns

It’s worth mentioning too that sometimes the nominative singular form of the noun is used as the plural. The following examples are when this can occur:

1. After ‘cá mhéad’ (how many): e.g. cá mhéad duine? – how many people
2. After ‘is iomaí’ (many): e.g. is iomaí uair – many hours
3. After ‘cúpla’ (a couple of): e.g. cúpla lá, cúpla focal – a couple of days, a couple of words
4. Often after cardinal numbers: e.g. trí lá, fiche uair, céad capall – three days, 20 hours, 100 horses

Declensions

I’ve already spoken about declensions here in realtion to all their forms. But to summarise:

First Declension

The first declension primarily consists of masculine nouns. But to summarise plurals in this declension:

• Nominative Plural: Often ends in -a, -anna, or -acha e.g. úll > úlla, carr > carranna, cineál > cineálacha.
• Genitive Plural: Sometimes the same as the nominative singular e.g. hataí na bhfear
• Some nouns have a “strong plural” ending e.g. carr, bealach, scéal
• Some nouns have a “weak plural” ending e.g. ceart, úll, cleas
• Some nouns undergo a vowel change before the slender consonant of the genitive singular/nominative plural e.g. ceann > cinn, poll > poill

Second Declension

The second declension is made up of mostly feminine nouns. To summarise plurals in this declension:

• Nominative plural: The plural nominative often ends in -a or -í. (e.g. bróg becomes bróga, seachtain > seachtainí)
• Genitive plural: The most common plural form in the second declension has a broad consonant followed by -a in the nominative, and a broad consonant alone in the genitive e.g. as above, nom. pl. bróga, gen pl. bróg. Bróg also an example of how sometimes the genitive plural is the same as the nominative singular in this declension as well.

Third Declension

The third declension is made up of both masculine and feminine nouns:

• In general, many words in this declension form the plural with one of the endings -anna or -acha
• Nominative Plural: there are quite a few ways to form the plural of the third declension:
  • Add -(a)í to most polysyllabic nouns which end in -éir, -eoir, -úir, óir, -cht, -úint, -irt (e.g.doctúir > dochtúirí, cáilíocht > cáilíochtaí)
  • Add -anna to the noun (e.g. am > amanna)
  • Add -acha to polysyllabic feminine nouns that end in slender consonants l, n or r (e.g. onóir > onóracha)
  • Add -ta to monosyllabic broad masculine and slender feminine nouns that end in l or n (e.g. gleann > gleannta, bliain > blianta)

Fourth Declension

The fourth declension is also made up of masculine and feminine nouns. 

• In general, many words of this declension form the plural with the following endings -tha/-t(h)e, -((e)a)nna, -((e)a)cha
• Nominative Plural: There are quite a few ways to form the plural of the fourth declension. Here are some of the most common ways:
  • The most common plural ending is -(a)í. (e.g. cailín > cailíní, páiste > páistí, piopa > piopaí)
  • Add -(i)the to nouns that end in (a)í, -aoi, -é (e.g. oibrí > oibrithe, draoi > draoithe, rúnaí > rúnaithe) Exceptions: dlí > dlíthe, rí > ríthe
  • Add -nna to nouns that end in -á, -eá, -ó, -eo, -ú, -ia, -ogha, -ua, -ao
• A standout noun that has a weak plural in this declension is bó (cow).

Fifth Declension

The fifth declension is made up mostly of feminine nouns.

• Nominative Plural: There are quite a few ways to form the plural of the fifth declension. Here are some of the most common ways:
  • Add -na / ne to feminine nouns that end in a vowel (and -n in the genitive singular) (e.g. comharsa > comharsana, traein > traenacha)
• The most common plurals are strong except for caora, faocha and lacha.

Irregular nouns

The following is a list of nouns that are declined irregularly:

*Note: talamh has two genitive singular forms, talún and talaimh but spelling wise, at least in dialectal Irish from Cork and Erris you’ll get “tailimh” as the normal genitive, but “talún” in set phrases and expressions like tinneas talún, os cionn talún srl.

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