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.
Syntax
Word order in Irish is of the form VSO (verb–subject–object) so that, for example, "He hit me" is [hit-past tense] [he] [me].
One distinctive aspect of Irish is the distinction between , the copula (known in Irish as ), and . describes identity or quality in a permanence sense, while temporary aspects are described by . This is similar to the difference between the verbs and in Spanish and Portuguese (see Romance copula), although this is not an exact match; and are cognate respectively with the Spanish and .
Examples are: . "He is a man." (Spanish , Portuguese ) . "He is cold (a cold-hearted person)." (Spanish , Portuguese ) . "He/Thomas is cold" (= feels cold) (Alt. Tá fuacht air [= "Cold is on him"]). (Spanish – in this case Spanish uses 'tener' (to have) instead of 'estar' (to be), Portuguese ) . "He is asleep." (Spanish , Portuguese ) . "He is good (a good person)." (Spanish , Portuguese ) . "He is well." (Spanish , Portuguese )
Nouns
Irish is an inflected language, having four cases: (nominative and accusative), (vocative), (genitive) and (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, and being masculine and feminine. While the neuter has mostly disappeared from vocabulary, the neuter gender is seen in various place names in Ireland.
Articles
The Irish definite article has two forms: and . may cause lenition, eclipsis, or neither. may cause eclipsis, but the only instance of lenition with is with the genitive singular of the word meaning first. is used in the common case singular for all nouns, and lenites feminine nouns. In the genitive singular, with lenition is used with masculine nouns, with feminine nouns. In the dative singular, 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). 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: "France," "Brazil," "Japan." Exceptions to this include "Ireland," "Scotland" and "England."
There is no indefinite article in Irish; the word appears by itself, for example: – "I have a pen", – "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 or to English the residence of the President, the flight of the Earls.
Adjectives
Irish adjectives always follow the noun. The adjective is influenced by the case, number and gender of the noun preceding it.
"The small girl" – masculine singular nominative
"The poor woman" – feminine singlar nominative
"The young boys" – masculine plural nominative
Adjectives in Irish have two morphological degrees of comparison: the positive (), e.g. "the boy is friendly", and the comparative (), e.g. "the girl is nicer than the boy". A superlative () sense is rendered by the comparative in a relative clause, e.g. "Seán is the nicest child of the three".
Adverbs
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 tapaigh, 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.