What is the "genitive?" Do other languages have this feature?

The long and the short of it: a noun that modifies another noun is in genitive relation to it. Most languages (I wanted to say all but then I thought of one possible exception) therefore have a genitive function. Many languages have special forms to indicate the genitive. A great many Indo-European languages, like English (barely)and Irish, are like this.

If you say 'my father's coat', 'father' is in genitive relation to 'coat'. The first noun modifies (or limits) the second. 'Sheila's new job' -- 'Sheila' is in the genitive. Other examples: 'a winter coat', 'a wool coat', 'a savings account', 'a milk carton', 'a summer day'. In English, we usually indicate the genitive by word order but we still show the genitive by ' 's ' too.

In Irish, there is often no special genitive form: tae, caife, bainne (tea, coffee, milk) stay as is: pota tae, muga caife, bosca bainne. Many others, however, do change in form:

an leabhar (the book), but: céad leathanach an leabhair (the book, the first page of the book)

Síle (Sheila): post nua Shíle (Sheila's new job)

fíon (wine): buidéal fíona (a bottle of wine)

biabhóg (rhubarb): gas biabhóige (a stalk of rhubarb)

Note that the describing (i.e., genitive) noun precedes the noun in English but follows it in Irish.

JP, a Chara,

If some of the jargon causes a problem, which it can, take a dip into the free on-line dictionaries. This is from 'A Web of Online D.s' :
...............................................
of, relating to, or constituting a grammatical case marking typically a relationship of possessor or source -- compare POSSESSIVE
2 : expressing a relationship that in some inflected languages is often marked by a genitive case -- used especially of English prepositional phrases introduced by of
- genitive noun
..........................................

So, JP's car = Carr JP.
(Your ending 'P' shows no inflection of course, but we still regard it as being 'in genitive'.)

But, an carr = the carr.

And JP of the car,
i.e. the JP gal/guy/fellow/stócach/girseach who is the owner of the said car = JP an chairr.

Those 'rr's are sounded and written so, i.e. they are inflected to let the listener know of this JP-car relationship. The 'i' which is inserted, shows us the change in quality of what is sounded. Sin agat an tuiseal ginide! That's the genitive, and nothing more.

There are a few other ways to make a genitive :
.............
Ciall = sense.

mórán céille = a lot of sense.
..............................
dochtúir = a doctor.

saol dochtúra = a doctor's life (or = life of a doctor)
..........................................................
geata = a gate.

druidim geata = closing of a gate (or = a gate's closing)
.......................................................
cathair = a city.

lár cathrach = a city center (or = center of a city)
.....................................................

Notice that 'geata' behaves like your 'P'; no change! That is to say, in total we are talking about four changes. The four changes to remember are :

carr > cairr
ciall > céille
dochtúir > dochtúra
cathair > cathrach

We can make those simple :

(And remember the none-change, 'geata', 'JP'.)

...r > ...ir
....l > ...ile
......ir > ......ra
.....ir > ....-r+ach

Simpler still, let C = any consonant :

> ..iC
> ..iCe
> ..Ca
> ..-+C


That's the guts of the Irish system. Four changes and a none change = Cúig Dhíochlaonadh = 5 declensions. Maybe 60% of Irish nouns behave like the first two, First and Second. Just look at those two and let the others come to you as you meet them.
.......................................................

While those rules can help to understand plurals, it is best to just forget them. That is, forget about declension when you cross into plural. Just think about two things : Weak and Strong!
For genitive in plural, we mostly, look to what we call 'strong'/tréaniolra and 'weak'/lagiolra plurals.

Weak means that it cannot maintain its plural form in plural genitive. It reverts to another form. (which happens to be singular!) Strong, of course, can keep its plural form through any mayhem of case.

Now, you don't have to remember the Strong plurals! Howcome? Just remember that there are two weak plurals; the narrowing of consonant type, like carr > cairr, and the addition of a final '-a' type :

...+a (as in 'fuinneog' > 'fuinneoga' = windows)

...iC (as in 'cairr' = cars)

Hence :

fuinneoga = windows;
plabadh fuinneog = slamming of windows;
plabadh na bhfuinneog = the slamming of the windows.

cairr = cars;
luas carr = speed of cars;
luas na gcarr = the speed of the cars.


You don't have to learn the others. You know if they're not weak, then, (difficult, isn't it?), yes, they're strong and can maintain their plural form :

na ceachtanna = the lessons;
foghlaim na gceachtanna = the/ learning of the lessons.

etc.

Some of us like to allow irregularity into the system, if it's there already in areas of speech, so, if JP has more than one carr and I'm describing JP as such :

JP na gcarr = JP of the cars;

or, if I'm into strong plurals today, to accomodate a listener :

JP na gcarrannaí = JP of the cars.

Both are fine.


Go n-éirí an Ghaeilg leat

Gabh mo leithscéal, a Sheosaimh, bail ó Dhia ort. Ní fhaca mé ansin thú nuair a thug mé faoi ar ball.

An Seosamh thoir.

Bhail, ní thig leis a rá nach bhfuair sé freagra ar a cheist! We aim to please.

An Seosamh thiar

Tá sé go hiontach! Go raibh maith agat.