I’d like to ask about plural forms of concrete nouns with the -acht suffix in those Munster dialects that still use dative plural forms.

Eg. if one says ar chosaibh, how would they say ‘the Gaeltachts’ and ‘in the Gaeltachts’? Would it be na Gaeltachta and sna Gaeltachtaibh, or na Gaeltachtaibh and sna Gaeltachtaibh? Or does anyone just uses Gaeltachtaí in plural?

I see that the -achtaí ending etymologically comes from the dative -achtaibh as pronounced by Connacht speakers, and originally the plural nominative was with -achta.

Searching through the corkirish blog I could find only two examples of such dative: nom. Connachta – dat. Connachtaibh (plurale tantum) and nom.sg. cómhacht, nom.pl. cómhachta, dat.pl cómhachtaibh (CO nom.sg. cumhacht, nom.dat.pl. cumhachtaí). Are those forms still used anywhere?

I started to wonder about it after I tried to write ‘in Gaeltachts’ using dative and realized that I have no idea if that should be i nGaeltachtaibh or i nGaeltachtaíbh. And then I realized that I have no idea what the plural nominative actually would be in Cork as Gaeltachtaí seems to be a Connacht form…

Actually I don't think the dative plurals in -aibh are regularly used anywhere nowadays. I think it can only be found in set phrases.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Thanks, I actually expected that, didn’t have much hope for even regular dative plural being still productive…

Anyway, what about the plural nominative? Do people in Munster use the forms cómhachtaí, Gaeltachtaí, which apparently come from the Connacht pronunciation of the datives in -achtaibh, or do they say Gaeltachtaibh, cómhachtaibh in nominative for plural, or do they use the old nominative Gaeltachta, cómhachta?

If they say Gaeltachtaí, then it’d be an interesting example of influence of a fellow dialect / caighdeán oifigiúil on a living speech (if my assumption that these forms originated in Connacht and come from -aibh is correct).

The dative plural is

Sna Gaeltachtaibh or sna Gaeltachtaí (based on the Nom. plural; its not influenced by compensatory lengthening as in Conamara, i.e. the -aibh to -aí).

Gaeltachta is the genitive singular.

The dative plural is still used, but rare. The dative plural endings have spread to the nominative plural for some words-especially first-declension/ o-stem nouns; hence, fearaibh and fir, and cinn and ceannaibh etc...

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Please wait for corrections/ more input from other forum members before acting on advice

Usually older grammar books teach that dative plural of nouns in -í is -íbh.

E.g. in foclóiríbh the í is long because of the nominative plural form foclóirí
foclóirí is due to the old ending -idhe (foclóiridhe)
So foclóiríbh is originally foclóiridhibh.

But in nouns in -achtaí it is -achtaibh with a short i.

The original plural of nouns in -acht is -achta
So I think you are right that -achtaí is due to -achtaibh.