Singular, Plural, and Dual

Irish nouns have three “numbers”: singular (for one item), plural (for multiple items), and a special form called the dual, which is used only with the number two. While the singular form is straightforward, forming the plural can be complex, with several different patterns and endings.

The Singular

The singular form, or an t-uatha, is the basic form of a noun you will find in a dictionary. It is used for a single countable item, for uncountable nouns, and, importantly, with most numbers.

You use the singular form of a noun in these cases:

• For a single item: bád amháin (one boat)
• For uncountable things: uisce (water), airgead (money)
• After the numbers 3–10, 13–19, and multiples of ten (20, 30, 40, etc.): trí bhád (three boats), deich mbád (ten boats).
• After cúpla (a couple/some) and cá mhéad (how many): cúpla bád (a couple of boats), cá mhéad bád? (how many boats?).

The Plural

The plural, an t-iolra, is used for more than one item when not counting with specific numbers. Plural formation in Irish is highly irregular, with many variations across dialects. It is not uncommon for a single noun to have several accepted plural forms. The lexicographer Niall Ó Dónaill once remarked that the word crann (tree) probably has more plural forms than there are trees in the Gaeltacht.

There are two main types of plural formation: weak plurals and strong plurals.

Weak Plurals

A weak plural (an lagiolra) is formed by making a small change to the noun’s stem, usually by altering the final vowel or adding a vowel ending. These plurals are most common in the first and second declensions.

• 1st Declension: The plural is often the same as the genitive singular.
  • leabhar (book) -> leabhair (books)
• 1st & 2nd Declensions: A common ending is -a.
  • cleas (trick) -> cleasa (tricks)
  • bróg (shoe) -> bróga (shoes)
• 3rd Declension: The -a ending is rare.
  • dreas (bramble) -> dreasa (brambles)

These are considered “weak” because they do not add a consonantal ending to the stem. For many nouns with a weak plural, the genitive plural form is the same as the nominative singular.

In some dialects, a strong plural ending is preferred even when a weak plural exists in the standard language. nasc (link) -> naisc (weak plural) or nascanna (strong plural)

Strong Plurals

A strong plural (an tréaniolra) is formed by adding a distinct ending containing a consonant to the noun’s stem. Common endings include -í, -acha, -anna, and -tha.

bás (death) -> básanna (deaths) rí (king) -> ríthe (kings) cailín (girl) -> cailíní (girls)

These are “strong” because the ending augments the stem with new consonants, making the plural form very distinct from the singular. In Modern Irish, these endings are generally the same in all cases (nominative, genitive, dative). Their popularity comes from this clarity; for example, nascanna is unambiguously plural, whereas the weak plural naisc is also the genitive singular of nasc.

The Counting Plural

While the singular form is normally used with numbers from 3-10, a special category of nouns uses a plural form instead. These are called counting plurals (an t-iolra comhairimh) and mostly apply to units of measurement, time, and money.

The counting plural is always a weak plural form. For some nouns, this form is used only for counting, while a different (often strong) plural is used in all other contexts.

The table below shows common nouns that use a counting plural. Forms that differ from the ordinary plural are in bold.

The form fichid is a remnant of the vigesimal (base-20) counting system, seen in phrases like trí fichid (three twenties) for sixty.

The Dual

The dual (an déach) is a special number form used only with the number two (dhá). It is a remnant of an older Indo-European system which had singular, dual, and plural. Today, if you are talking about two things without using the number dhá, you must use the plural.

The form of a noun in the dual is almost always identical to its dative singular form. This is most commonly seen with paired body parts.

• cos (one foot)
• dhá chois (two feet)
• ar an gcois (on the foot - dative singular)

Remnants of the Dual System

The dual system affects not just the noun but also the article and following adjectives.

1. The Dual Article: The article used with dhá is an, the singular article, not the plural na.

   • an dá bhád (the two boats)
   • Compare: na trí bhád (the three boats)

2. The Dual Noun Form: After dhá, a noun takes its dual form if it has one (which is its dative singular form). If it does not have a distinct dual form, it simply uses the nominative singular.

   • dhá láimh (two hands - lámh has a dual form)
   • dhá bhád (two boats - bád uses the singular form)

3. Adjectives in the Dual: An adjective that follows a noun in the dual takes its plural form. This can look unusual, as a singular-looking noun is followed by a plural adjective.

   • an dá bhád mhóra (the two big boats)
   • an dá chois mhóra (the two big feet)

This rule also applies after beirt, the personal number for two people.

• an bheirt bhan óga (the two young women)

Genitive Case in the Dual

The genitive case of a dual noun follows two patterns:

• For nouns with a weak plural, the genitive dual is the same as the genitive plural.
  • cuma a dhá chos (the shape of his two feet)
• For nouns with a strong plural, the genitive dual is the same as the nominative singular.
  • gramadach an dá chanúint (the grammar of the two dialects)

When referring to two items with a pronoun, you use the plural pronoun siad/iad (they/them). The verb can be in either the singular or plural form. Thángadar an dá chapall anall. (The two horses came over.)