Irish adjectives have three declensions, each with the same case structure as the nouns (nominative, vocative, genitive, dative). The adjectives agree with nouns in case, plurality[1] and gender.[2]
The three declensions are classified by their endings: consonants; ‑úil, ‑ir; vowels. The genitive singular forms are analogous to noun declension forms:
Plurals are generally formed with the suffix ‑a. They are considered weak or strong according to the noun they qualify, and the same rule applies to the genitive plural: when weak, it is the same as the nominative singular; when strong, it is the same as the nominative plural.
Syncopation occurs in some first declension adjectives in the genitive singular feminine, and plural. Many such plurals retain the genitive's slender form in + e.
The comparative (and superlative) is formed regularly using the genitive singular feminine. There is a small set of irregular comparatives.
Irish adjectives undergo initial mutation, by lenition only.[5] In the singular, agreement follows the pattern[6] of the qualified noun. In the plural, there is in general no lenition.[7] Any lenition occurs across all qualifying adjectives.[8] The dentals rule does not apply.[9]
| 1st | 2nd | 3rd | |||||
|---|---|---|---|---|---|---|---|
| Gender | m | f | m | f | m & f | ||
| Singular | Nom | consonant | ‑úil, ‑ir | vowel | |||
| Voc | slender | - | - | - | |||
| Gen | slender [10] | + e | - | + a | - | ||
| Dat | - | slender [11] | - | - | |||
| Weak Plural Noun | Nom | + a/e[12] | + a | - | |||
| Voc | + a | + a | - | ||||
| Gen | - | - | - | ||||
| Dat | + aibh [13] | + aibh | - | ||||
| Strong Plural Noun | Nom | + a | + a | - | |||
| Voc | + a | + a | - | ||||
| Gen | + a | + a | - | ||||
| Dat | + aibh [13] | + aibh | - | ||||
Irish first declension adjectives end in consonants (other than the second declension ‑úil and ‑ir).
The genitive singular masculine (gsm) is formed in general by slenderising, although there are exceptions (and exceptions to the exceptions). The genitive singular feminine (gsf) form is analogous to the noun second declension, that is, with suffix ‑e. The plural in general is formed with suffix ‑a, but the genitive obeys the weak/strong rule in agreement with the noun qualified.
Adjectives whose gsm is not slenderised are [14]:
The gsf of (polysyllabic) adjectives ending in ‑ach is written ‑aí < aighe.
Slender adjectives have natural plurals in + e, e.g., ait, npl aite, maith, npl maithe.
When forming first declension genitive singular feminine, and plurals, unstressed vowels are often syncopated.
A couple of nouns are not syncopated in the genitive, but are in the plural.
If the root is slender, the plural may remain slender.
An extreme case is álainn, which loses the whole syllable:
| mór (“big”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | mór | mhór | móra |
| Voc | mhóir | mhór | móra |
| Gen | mhóir | móire | mór |
| Dat | mór | mhór | móra |
| fliuch (“wet”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | fliuch | fhliuch | fliucha |
| Voc | fhliuch | fhliuch | fliucha |
| Gen | fhliuch | fliche | fliuch |
| Dat | fliuch | fhliuch | fliucha |
| ramhar (“fat”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | ramhar | ramhar | ramhra |
| Voc | ramhair | ramhar | ramhra |
| Gen | ramhair | raimhre | ramhar |
| Dat | ramhar | ramhar | ramhra |
Irish second declension adjectives end in ‑úil and ‑ir.
The genitive singular masculine (gsm) of second declension adjectives, being already slender, is the same as the nominative singular. The genitive singular feminine (gsf) form is analogous to the noun third declension, that is, with suffix ‑a. The plural in general is formed with suffix ‑a, but the genitive obeys the weak/strong rule in agreement with the noun qualified.
The adjectives in ‑úil are derived from (s)amhail.[16]
The adjectives in ‑ir are syncopated when adding the suffix ‑a, for example, deacair, gsf, npl. deacra.
| suimiúil (“interesting”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | suimiúil | shuimiúil | suimiúla |
| Voc | shuimiúil | shuimiúil | suimiúla |
| Gen | shuimiúil | suimiúla | suimiúil |
| Dat | suimiúil | shuimiúil | suimiúla |
| deacair (“difficult”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | deacair | dheacair | deacra |
| Voc | dheacair | dheacair | deacra |
| Gen | dheacair | deacra | deacair |
| Dat | deacair | dheacair | deacra |
Irish third declension adjectives end in vowels.
There are no changes to third declension adjective endings.[17]
| crua (“hard”) | Singular | Weak Plural [15] | |
|---|---|---|---|
| m | f | m & f | |
| Nom | crua | chrua | crua |
| Voc | chrua | chrua | crua |
| Gen | chrua | crua | crua |
| Dat | crua | chrua | crua |
There are very few irregular adjectives in Irish. The irregular forms get reused for the comparative.
Comparatives are formed regularly by using the genitive singular feminine (gsf) form.
There are a few irregular comparatives. A small subset has different sources than the radical:
Fada has both irregular and regular variants:
The irregular adjectives use their irregular form:
Others have irregular variants:
There is also a couple of defective adjectives, with comparatives only:
{{ga-decl-adj}}, general template