Just like verbs have different tenses, nouns can have different cases, depending on their function in a sentence. In English you can still see this in personal pronouns, such as ‘I’ and ‘me’ (which are different cases of essentially the same word).
The genitive case is a form used to denote the possessor of something else (again, we see this in personal pronouns: ‘my, mine’). In English, cases only exist in personal pronouns, but in many languages, they also apply to nouns. An example of this is the Latin phrase ‘Agnus Dei’, meaning ‘lamb of God’. As you can see, there is no word translating as ‘of’. Instead, ‘Dei’ is marked as the possessor by being in the genitive case (as opposed to the nominative case ‘Deus’).
Irish has four different cases: Nominative, Genitive, Vocative and Dative/Prepositional.
The nominative is the ‘normal’ case of a word, and is used for the subject and the object of the case, i.e. the person/thing acting out the action of the verb, and the person/thing undergoing it. In “Itheann an fear cáca” (The man eats a cake), “an fear” is the subject and “cáca” is the object. They are both in the nominative case.
The Prepositional (which is more commonly called the Dative), is, as the name suggests, used after prepositions. In modern Standard Irish, the Dative is always identical to the nominative, except for the word “Éire” (Ireland), which has the Dative form “Éirinn”. Some dialects also still have a distinct dative for some words. The definite article too still reflects the dative case, in the singular is does this by causing eclipsis: “leis an bhfear” (with the man) >< “an fear” (the man).
The Genitive, as has been explained, denotes the possessor of something else. Irish has a special rule which says that when a noun in the genitive (a possessor) is combined with another noun (his/her/its possession), only one of them may have the definite article. When both would have the article, it is the possessor that takes it, hence “Ainm an mhic” translating as “The name of the son”.
The Vocative, finally, is used to directly address the person you are speaking too. If you were to ask “Mummy, can I have a biscuit?” in Irish, the “mummy” would be in the Vocative case. The Vocative case is usually preceded by the word “a” which triggers lenition. In many cases, the vocative is identical to the nominative, but this is not always the case.
“an” here is singular. It’s “the name of the son” = the son’s name. In Irish, masculine nouns of the first declension use the plural nominative form also for the genitive singular. In the genitive case, masculine nouns of the first declension get lenited. Thus:
- son = mac
- the son = an mac
- sons = mic
- the sons = na mic
- of the son = an mhic
- of the sons = na mac
This is just Duolingo’s way to gently prepare us for the genitive skill! :)