The morphology of Irish is in some respects typical of an Indo-European language. Nouns are declined for number and case, and verbs for person and number. Nouns are classified by masculine or feminine gender. Other aspects of Irish morphology, while typical for an Insular Celtic language, are not typical for Indo-European, such as the presence of inflected prepositions and the initial consonant mutations. Irish syntax is also rather different from that of most Indo-European languages, due to its use of the verb–subject–object word order.^[1]

This article relies largely or entirely on a single source. (June 2020)

Word order in Irish is of the form VSO (verb–subject–object) so that, for example, "He hit me" is Bhuail [hit-past tense] sé [he] mé [me].

One distinctive aspect of Irish is the distinction between is, the copula (known in Irish as an chopail), and tá. Is describes identity or quality in a permanence sense, while temporary aspects are described by tá. This is similar to the difference between the verbs ser and estar in Spanish and Portuguese (see Romance copula), although this is not an exact match; is and tá are cognate respectively with the Spanish es and está.

Examples are:

• Is fear é. "He is a man." (Spanish Es un hombre, Portuguese (Ele) é um homem)
• Is duine fuar é. "He is cold (a cold-hearted person)." (Spanish Es frío, Portuguese (Ele) é frio)
• Tá sé/Tomás fuar. "He/Thomas is cold" (= feels cold) (Alt. Tá fuacht air [= "Cold is on him"]). (Spanish Tiene frío – in this case Spanish uses tener (to have) instead of estar (to be), Portuguese (Ele) está com frio)
• Tá sé ina chodladh. "He is asleep." (Spanish Él está durmiendo, Portuguese Ele está a dormir)
• Is duine maith é. "He is good (a good person)." (Spanish Es bueno, Portuguese (Ele) é bom)
• Tá sé go maith. "He is well." (Spanish Está bien, Portuguese (Ele) está bem)

This section does not cite any sources. (June 2023)

Irish is an inflected language, having four cases: ainmneach (nominative and accusative), gairmeach (vocative), ginideach (genitive) and tabharthach (prepositional). The prepositional case is called the dative by convention.

Irish nouns are masculine or feminine. To a certain degree the gender difference is indicated by specific word endings, -án and -ín being masculine and -óg feminine. While the neuter has mostly disappeared from vocabulary, the neuter gender is seen in various place names in Ireland.

The Irish definite article has two forms: an and na. An may cause lenition, eclipsis, or neither. Na may cause eclipsis, but the only instance of lenition with na is with the genitive singular of the word céad meaning first. An is used in the common case singular for all nouns, and lenites feminine nouns. In the genitive singular, an with lenition is used with masculine nouns, na with feminine nouns. In the dative singular, an may cause lenition or eclipsis depending on the preposition preceding it and on regional norms (in Ulster usage, lenition is standard with all prepositions, while in other regions eclipsis is used with many). Na is the only plural form of the article; it causes eclipsis in the genitive for both genders, and no mutation in other cases.

Names of countries usually take the definite article in the nominative: An Fhrainc "France", an Bhrasaíl "Brazil", an tSeapáin "Japan". Exceptions to this include Éire "Ireland", Albain "Scotland" and Sasana "England".

There is no indefinite article in Irish; the word appears by itself, for example: Tá peann agam. – "I have a pen", Tá madra sa seomra. – "There's a dog in the room".

When two definite noun phrases appear as part of a genitive construction (equivalent to the X of the Y in English), only the noun phrase in the genitive takes the article. Compare Áras an Uachtaráin or Teitheamh na nIarlaí to English the residence of the President, the flight of the Earls.

Irish adjectives always follow the noun. The adjective is influenced by the case, number and gender of the noun preceding it.

• An cailín beag "The small girl" – masculine singular nominative
• An bhean bhocht "The poor woman" – feminine singular nominative
• Na buachaillí óga "The young boys" – masculine plural nominative

Adjectives in Irish have two morphological degrees of comparison: the positive (Irish: bunchéim), e.g. Tá an buachaill cairdiúil "the boy is friendly", and the comparative (breischéim), e.g. Tá an cailín níos cairdiúla ná an buachaill "the girl is nicer than the boy". A superlative (sárchéim) sense is rendered by the comparative in a relative clause, e.g. Is é Seán an páiste is cairdiúla den triúr "Seán is the nicest child of the three".

Irish adverbs are used to modify verbs, adjectives and other adverbs.

An adverb can be created from an adjective by adding go before it, e.g. go mall, go tapaidh, go maith, etc. If the adjective begins with a vowel, ⟨h⟩ is added before it, e.g. go hálainn, go híseal, go háirithe, etc.

Adverbs can often be created from nouns by putting a preposition before them, e.g. ar bith, de ghnáth, faoi dheireadh, etc.

Other categories of adverbs include the following:

Adverbs that describe relation to time, e.g. uaireanta, anois, cheana, etc.

Adverbs that describe relation to place, e.g. ann, abhaile, amuigh, etc.

Adverbs used in questions, e.g. cathain?, conas?, cá?, etc.

Adverbs used for negation, e.g. ní, nach, nár, etc.

Other adverbs, e.g. áfach, chomh maith, ach oiread, etc.

There are two conjugations and 11 irregular verbs. Tenses or moods are formed by inflecting the stem, and in the past and habitual past tenses and the conditional mood also by leniting any initial consonant. The inflected tense and mood forms are: present indicative, present habitual indicative (differs from present only in the verb bí "to be"), future, past indicative, past habitual indicative, conditional, imperative, present subjunctive, and past subjunctive. Verbs also have a verbal noun and past participle, and progressive constructions similar to those using the English present participle may be formed from the verbal noun and an appropriate tense of bí. Examples of tense conjugations: (all third person forms without subject pronoun):

• 1st conjugation: Fág "to leave" – d'fhág (past) – fágann (present) – fágfaidh (future) – d'fhágfadh (conditional) – d'fhágadh (habitual past) – fága (subjunctive) – fágadh (imperative)
• 2nd conjugation: Ceannaigh "to buy" – cheannaigh (past) – ceannaíonn (present) – ceannóidh (future) – cheannódh (conditional) – cheannaíodh (habitual past) – ceannaí (subjunctive) – ceannaíodh (imperative)
• Irregular: Téigh "to go" – chuaigh (past) – téann (present) – rachaidh (future) – rachadh (conditional) – théadh (habitual past) – té (subjunctive) – téadh (imperative)

In addition to the passive voice, there is the impersonal form of the verb, termed the saorbhriathar or "autonomous verb", which serves a similar function (the most literal translation is "You/One/They...[e.g. say, are, do]").

Verbs can be conjugated either synthetically (with the personal pronoun included in the verb inflection) or analytically (with the verb inflected for tense only and a separate subject). However, the official standard generally prescribes the analytic form in most person-tense combinations, and the synthetic in only some cases, such as the first person plural. The analytic forms are also generally preferred in the western and northern dialects, except in answer to what would in English be "yes/no" questions, while Munster Irish prefers the synthetic forms. For example, the following are the standard form, synthetic form and analytical form of the past tense of rith "to run":

There are three kinds of cardinal numbers in Irish: disjunctive numbers, nonhuman conjunctive numbers, and human conjunctive numbers.

A notable feature of Irish phonology is that consonants (except /h/) come in pairs, one "broad" (velarized, pronounced with the back of the tongue pulled back towards the soft palate) and one "slender" (palatalized, pronounced with the middle of the tongue pushed up towards the hard palate).

Diphthongs: /iə/, /uə/, /əi/, /əu/.