Why is cat eclipsed, I thought chuig+an is not one of the prepositions that require eclipsis?
Initial Mutations after chuig
•without an article: no lenition or eclipsis e.g. chuig cailín = to a girl
•with the singular-article: eclipsis (except d,t) e.g. chuig an gcailín = to the girl
■in Munster, d,t also eclipses
■in Connacht, t-prefix precedes femin. nouns with s-: chuig an tsúil
■in Ulster, always lenition e.g.: chuig an chailín
The reason this eclipsis case may come up as a surprise is that chuig + an was not listed in the Eclipsis tips and notes (and right under the table, it mentions Other prepositions used with an (for example, idir an between the) do not cause eclipsis).
I saw somewhere that all preposition + article combinations cause eclipsis but I can't find it now. Is this right?
Not all of them, but most. And it does, in Connacht and Munster Irish. However, in Ulster Irish, it causes lenition instead.
Chun tends to be used in Munster Irish. Chun takes the genitive, e.g. chun an chait, while chuig doesn’t.
In addition to scilling's answer, I would usually use 'chun' to mean 'in order to'. For example, 'chuaigh mé go dtí na siopaí chun cáis a cheannach' = 'I went to the shops in order to buy cheese'. Chuig might be used in this instance too; I don't actually know.
Oh yeah, woops! I just think about cheese too much. It's a problem.