Historically, the Irishdeclined prepositions developed from the merger of the independent preposition and the possessive pronoun. There is also a set ofundeclined prepositions.

Simple prepositions govern thedative case (with some exceptions), while derived prepositions govern thegenitive.

Prepositions may triggerinitial mutations on proceeding words.

In Modern Irish, simple prepositions nearly always govern the dative,akaprepositional, with a few exceptions governing theaccusative.^[1] Derived prepositions govern thegenitive. In the lists below, prepositional governance is assumed unless otherwise indicated.

The declined prepositions are:^{[rfi 1]}

ag,ar,as,chuig,de,do,faoi,fara,i,idir,^{a, p[rfi 2]}ionsar,le,ó/ua,roimh,thar,trí,um.

The undeclined prepositions are:

a,amhail^a,dar,gan^a,go/go dtí^a,is,mar,^{[rfi 3]}os,seachas^a.

One-word prepositions derived from substantives, all governing the genitive and all undeclined, include:

cois^g,fearacht^g,tigh^g,timpeall^g,trasna^g.

The prepositionchun^g is ultimately derived from a verb, governs the genitive, and is declined using the personal forms ofchuig.

All two-word prepositional phrases^[2] govern the genitive. Most are formed as combinations of a preposition plus a substantive, e.g.,ar nós,i ndiaidh,tar éis^[3] etc.

• The prepositionionsar =i +ar is declined asar.
• Three prepositions ending in vowels (le, fara, trí (sg only^[10][11])) use the 3rd sgm form before the article, e.g.leis an....
• Prepositions ending in vowels (de, do, faoi, i, le, ó, trí) undergo contractions with other parts of speech, in particular the article. These forms are summarised in the Wiktionary template{{ga-preposition contractions}}.
• Some contractions with the article, especially those ofi, retain thes of Proto-Celtic*sindos:
  • i + an → insan > sa(n)^[12]
  • i + na → insna > sna
  • dialectic variants:
    • de + na → desna
    • do + na → dosna.

The third person forms of Old Irish simple prepositions are case dependent (accusative or prepositional). The singular masculine forms are irregular,^[13] but the singular feminine, and the plural forms are tractable:^[14]

In modern Irish, onlyfara has + e in the 3rd sgf, although it is not derived from an Old Irish preposition, but rather fromferr (the comparative ofmaith). All others have standardised to + i.

In the 3rd pl, onlyde anddo have + ibh. All others have standardised to + u. The 3rd pl ofle (leo) derives directly from an Old Irish variant.

The simple prepositions may triggerinitial mutations on proceeding words. The paradigm in Modern Irish is very similar to Old Irish (cf. Etymology below), with a few exceptions, notably:

• the "mixed mutation" prepositions:idir, ar, thar, gan
• those derived with significant changes:as,chuig,roimh
• amhail

In Old Irish, the articlein triggers case-dependent mutations. In the singular, the accusative triggers eclipsis, while the prepositional triggers lenition.

As prepositional grammar evolved in Modern Irish, the dialects diverged. Ulster Irish^[18] favoured the prepositional lenition, while the others, the accusative eclipsis.

In summary, for prepositions governing the dative, with the singular article:

• Ulster Irish: lenition
• Other dialects: eclipsis, except:
  • faoin,ón,sa: lenition (Munster)
  • den,don,san: lenition

Notes

• lenition is subject to thedntls rule
• lenition tends to trigger t-prothesis ons, especially for feminine nouns, e.g.,sa tsráid
• eclipsis tends not to occur ond/t, e.g.,ag an doras

Other prepositions:

• a^{[ep 4]} <do
• dar <de/do + ar
• go dtí: re-purposed archaic present subjunctive oftar

Other Old Irish prepositions:

• fíad^{L, p}
• ís: antonym ofúas; whencesíos etc.

• {{ga-prep-infl}}
• {{ga-preposition contractions}}

• The History of the Prepositions on Akerbeltz.
• Prepositions onNualéargais.

• Wiktionary:Irish entry guidelines

• Category:Irish language
• Category:Irish appendices
• Category:Irish prepositions

• Irish terms inherited from Proto-Celtic
• Irish terms derived from Proto-Celtic
• Irish terms inherited from Old Irish
• Irish terms derived from Old Irish
• Irish appendices
• Preposition appendices