Tá mé ar an bhealach.
Tá mé ar an mbealach.

"I'm on my way."

An Irish friend of mine was teaching me some Irish, but he said he forgot which was correct...

Any help, please? Thanks ^_^

Either, today. Donegal is mostly lenition and the West and Munster, eclipses.

There was once a difference for location and direction, so it would be 'ar an bhealach' (on the road) and 'chug an mbealach' (towards the road), in the logic (the words theme selves would also have changed if possible, but that's a separate story)

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ar an bhealach (proper dative)
ar an mbealach (accusitive)

The accusative case was traditionally used to express movement and is marked by an urú.
The dative case was always marked with a séimhiú.

It still exists today in the fossilised phrases isteach and istigh, and amach and amuigh.

i.e. Táim ar mo shlí/ ag dul isteach

Táim ag dul isteach (accusitive = movement)

i = preposition -i- = in

teach = house

s = historical -s-, found in leis an, ins an etc...

but,

Táim istigh (dative)

Tigh being the dative form of te(a)ch, and exists in the Nominative in Munster tigh, Scottish and Ulster Gaelic toigh/ taigh and Manx thie.

When the accusative collapsed**, or the idea of movement collapsed and the categorisation of the prepositions became less rigid, the dative case became the norm following a prepsition + the article. But in Munster and Connacht, the accsitive's initial mutation i.e. an t-urú was adopted over the traditional dative séimhiú.

There is evidence to suggest that fragments of the accusative remained in existence with Irish speakers of the 40s and 50s.

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

Actually the "normal" form is "teach" in most of Ulster, but at the same time, you can use the dative form "toigh" to indicate motion or situation:

D'fhan sé toigh s'againne.
Chuaigh sé toigh Sheáin.
But: Tá teach beag thall.

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

Autocorrect gets more invasive by the day....

As a point of curiosity, it's the loss of the accusative/dative distinction that has led Irish to have "-igh" as a slenderisation of "-ach". Scottish Gaelic doesn't do this (except in Islay, and nearby), instead going with "-ich". Essentially ScG lost the dative and the accusative ending became normal, and Irish lost the accusative and the dative ending became normal. Except with "house", where Irish kept the dative "teach" and ScG the accusative "taigh", for no obvious reason (and both languages retain both in the adverbial forms).

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A language belongs to its native speakers, and when you speak it, you are a guest in their homes.
If you are not a good guest, you have no right to complain about receiving poor hospitality.

it's exactly the same ending, but not pronounced the same way.

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

You're all amazing

Thanks a lot!

What does this mean? That those are no longer in use?

The accusative case merged with the nominative long ago.
Only nominative, genitive, vocative and dative still exist in Modern Irish (and Scottish Gaelic).

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

There is no real functional dative anymore, even if as Lughaidh has shown there are some relics like 'toigh', and maybe there are some old people with lámh/láimh, bos/bois, cos/cois in Cork or Kerry as that would be more of a 'prepositional case' and not really marking a dative as it would use eclipsis or lenition along lines suitable to that person's dialect, so the initial mutation is kind of like a historical reflex of an originally more specific pattern. We could mention initial mutation on adjectives, such as ar an chapall bhán instead of the older (but historically newer as it would be post dative/accusative loss) Munster 'ar an gcapall mbán'

The grammar books could do like the Christian Brothers' book and call the cases, the common, genitive and vocative and mention the variance seen above.

You see, lots of 'nominative' word forms are old prepositional/dative forms, especially for feminine nouns (ex: láimh, once lámh, and coill, once coll) and even for masculine nouns in pronunciation (suich as cat said like 'cut'). It is also the case that genitive (Conamara gaeidhige not gaeidhilg) and maybe accusative forms also became the common form, so thanks to both oral transmission and the inertia (and friction) of the written word, there exists are sorts of declensions and variant forms that come down to us by way of slightly messy routes

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