introduces the vocative case causes aspiration
a Sheáin Seán!
a Shinéad Sinéad!
a dhuine hey you!
introduces a bare numeral prefixes h to vowels
a haon, a dó, a trí one, two, three
uimhir a haon déag number eleven
seomra a ceathair room four
connects objects with verbal nouns causes aspiration
ní féidir liom an obair a dhéanamh I can't do the work
an bhfuil tú chun an cheist a fhreagairt? are you going to answer the question?
ba mhaith liom tú a phógadh I would like to kiss you
introduces a direct relative clause that,
which,
who with independent form of verbs,
causes aspiration an fear a bhí ann the man who was there
an duine a chonaic tú the person (that) you saw
introduces an indirect relative clause whose,
whom with dependent form of verbs,
causes eclipsis an fear a raibh deacrachtaí aige the man who had difficulties
an duine a bhfaca tú a mhac the person whose son you saw
all,
what with dependent form of verbs,
causes eclipsis sin a bhfuil that's all
sin a bhfuil agam that's all I have
léigh sí a raibh scríofa ann she read what was written there
introduces a noun of degree
ní chreidim a mhéad atá sé I can't believe how big it is
tá moladh ag dul dó as a fheabhas a d'oibrigh sé he deserves praise for how well he worked