Compound Prepositions in Irish

Overview

Compound prepositions are two-word (or multi-word) prepositions that function as a single unit. Unlike simple prepositions (ar, le, i), compound prepositions consist of a simple preposition plus a noun, and they require the following noun to be in the genitive case. They are essential for expressing complex spatial, temporal, and logical relationships.

Common compound prepositions include ar feadh (for the duration of), i rith (during), de bharr (because of), in aice le (near), os comhair (in front of), and i ndiaidh (after). These appear constantly in both spoken and written Irish and are often the only way to express certain meanings.

Because compound prepositions trigger the genitive case, using them correctly requires knowledge of genitive forms. This intersection of prepositions and case makes compound prepositions an excellent practice ground for consolidating your genitive case skills.

How It Works

Common Compound Prepositions

Irish	English	Genitive required
ar feadh	for the duration of	ar feadh na hoíche
i rith	during	i rith an lae
de bharr	because of	de bharr na drochaimsire
in aice le	near / beside	in aice leis an scoil
os comhair	in front of / opposite	os comhair na scoile
i ndiaidh	after	i ndiaidh an dinnéir
ar son	for the sake of / on behalf of	ar son na síochána
in éadan	against	in éadan an dlí
i measc	among	i measc na ndaoine
le linn	during (a person's time)	le linn an chogaidh
tar éis	after	tar éis na hoibre
de réir	according to	de réir an dlí

With Definite Nouns (Genitive)

Compound Prep.	+ Genitive	English
ar feadh	na hoíche	for the whole night
i rith	an lae	during the day
de bharr	na drochaimsire	because of the bad weather
os comhair	na scoile	in front of the school
i measc	na ndaoine	among the people
de réir	an dlí	according to the law

With Pronouns

Some compound prepositions combine with pronouns through the possessive:

Compound Prep.	+ "me"	Example
os comhair	os mo chomhair	in front of me
i ndiaidh	i mo dhiaidh	after me
ar son	ar mo shon	on my behalf
in éadan	i m'éadan	against me

Examples in Context

Irish	English	Note
Ar feadh na hoíche.	For the whole night.	Genitive: oíche → hoíche
De bharr na drochaimsire.	Because of the bad weather.	Genitive: drochaimsir → drochaimsire
I rith an lae.	During the day.	Genitive: lá → lae
Os comhair na scoile.	In front of the school.	Genitive: scoil → scoile
I measc na ndaoine.	Among the people.	Genitive plural + eclipsis
De réir an dlí.	According to the law.	Genitive: dlí → dlí
Ar son na síochána.	For the sake of peace.	Genitive: síocháin → síochána
Le linn an chogaidh.	During the war.	Genitive: cogadh → chogaidh
Tar éis na hoibre.	After the work.	Genitive: obair → oibre
In aice leis an siopa.	Near the shop.	"le" + article

Common Mistakes

Forgetting the genitive after compound prepositions

• Wrong: ar feadh an oíche
• Right: ar feadh na hoíche
• Why: Compound prepositions require the genitive case. Oíche (feminine) takes the genitive article na and gets h-prefix.

Using nominative instead of genitive noun forms

• Wrong: i rith an lá
• Right: i rith an lae
• Why: Lá changes to lae in the genitive case.

Confusing compound and simple prepositions

• Wrong: ar feadh le Máire (treating it like a simple preposition)
• Right: ar feadh ama Mháire (for the duration of Máire's time)
• Why: Compound prepositions are followed by a noun in the genitive, not by another preposition.

Usage Notes

Compound prepositions are equally common in spoken and written Irish. Some, like i ndiaidh and tar éis, are interchangeable in meaning but have dialectal preferences: tar éis is more standard while i ndiaidh is particularly common in Connacht. Others, like de bharr and de réir, are used in all dialects without variation. When compound prepositions take pronoun objects, the possessive pronoun system creates forms like os mo chomhair (in front of me), i do dhiaidh (after you).

Practice Tips

1. Take five compound prepositions and use each with three different nouns, paying attention to the genitive forms: ar feadh na seachtaine (for the week), ar feadh an tsamhraidh (for the summer), ar feadh na bliana (for the year).
2. Practice the pronoun forms: convert os comhair na scoile (in front of the school) to os mo chomhair (in front of me), os do chomhair (in front of you), etc.

Related Concepts

• Simple Prepositions — the basic prepositions that compound prepositions build on