Hi all! I am finally just going to ask:

What is a genitive and when do we use it ?

The short answer is when we say something of something but it's not always quite as simple as that.

The genitive is used in a lot of places in Irish:

It's what's used for the possessive case:

Seán's house: Teach Sheáin ("Seán" here is in the genitive case)

As Scooby said, it's used in many places where we would use "of" in English:

The Women of Ireland: Mná na hÉireann ("Éireann" is the genitive case of "Éire")

It's also used to turn a noun into an adjective:

Toothache: Tinneas Fiacaile ("Fiacaile" is the genitive singular of "Fiacail": Tooth)

It's also used after compound prepositions (os comhair, os cionn, etc.) and in constructions using "ag" plus the verbal noun.

Redwolf

Prepare for one of the most comprehensive answers you are likely to get on the forum. Why can I sense people cringing at the idea of me explaining this.....? O.k. click on the link below. Lady Wombat is slightly more reliable than me on this one.

This link is about when the tuiseal ginideach is used: viewtopic.php?f=34&t=840

There are other related links there too.

viewtopic.php?f=28&t=838 (genetive singular info)
viewtopic.php?f=28&t=839 (genetive plural info)

_________________

To put it in the context of English: although the genitive case has largely disappeared in English, we still use it in cases of possession (and some related ideas):
If Mary has a book, it it Mary's book. The "apostrophe + s" creates the genitive form of Mary, with the meaning being "the book of Mary". Use of an "s" (or "es") is the customary way to create a genitive in many Germanic languages (English is basically a Germanic language with a lot of vocabulary from other languages). In fact, the apostrophe is a somewhat modern convention. The original form would just have been "Marys book".

Since few people learn about this as a genitive ending, it leads to all sorts of silly arguments. When I was in school, teachers would sometimes say that the "apostrophe + s" ending could only be used with people, and that an expression like "the building's roof" was incorrect, and instead one should say "the roof of the building". They were simply using a French-based form in place of the Germanic-based form. Since Norman French gave so much vocabulary (and some grammar) to the mix which became modern English, we have the flexibility to use both forms.

_________________
I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

Actually, the apostrophe replaces an e that was at first pronounced but gradually became silent. The singular genitive ending in Old English (Anglo-Saxon) was -es. In Middle English, it would have been "Maryes book".

The apostrophe after s in plural genitives, on the other hand, is a much later invention unrelated to Old English.

_________________
Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).

We need a "phew, thank goodness that's over/I finally have that explained" emoticon (With a shorter name...Maybe just "phew"... )!!! Thank you everyone! (Especially Wombat's explanation! - Thank you, a Shaoirse, for the link!) There is just one part for now I'm going to point out a bit of confusion:



Sorry, I which is the verbal noun?





I like that better Wonder what would happen if you wrote that on an English test? Go in pleading your case!!

In those sentences, the verbal noun is the word that follows "ag." In Irish, "ag" plus the verbal noun is the equivalent of a verb with the "-ing" ending (standing, sitting, eating, etc.). That construction is followed by the genitive.

Redwolf

... when it is used with the verb to be:

I am eating = Tá mé ag ithe.

but in English, there are plenty of other contexts in which you would use the verb+ing, and that you wouldn't translate with "ag+verbal noun" in Irish. Many learners make mistakes with that

_________________
Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Believe it or not, but native speakers make many mistakes as well (in any language)