Can someone remind me of the rules governing lenition of a genitive noun that's modifying another noun? (For example: love triangle, beer glass, etc.). I've been navigating this by the seat of my pants for years, but I don't think I've ever actually learned the rules (this is assuming there isn't a definite article in the way).

Redwolf

Here's Gramadach na Gaeilge's page on lenition in the gentive. There's quite a lot of rules, and a decent amount of "exceptions". However, three big ones for leniting are mentioned:

1) lenited after masculine nouns in the weak plural (on slender consonants) (na fir chéile)
2) lenited after masculine nouns, that are in the genitive themselves (on slender consonants) (teach pobail bhaile)
3) lenited after feminine nouns in the nominative singular (bean chéile)

However, there's a few exceptions listed for (3).

A Redwolf, nach bhfuil cóip agad do New Irish Grammar nó do Ghraiméar Gaeilge na mBráithre Críostaí nó do A Grammar of Modern Irish (Pól Ó Murchú)?

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

Níl, faraor! Ceann (nó dhó) eile don buiséad!

galaxyrocker, grma!

Redwolf

Goidé mar a d'fhoghlaim tú Gaeilg gan amhanc ar leabhar ghramadaí ar bith? Bhail, is féidir nach bhfuil mé ábalta sin a thuigbheáilt siocair gur gramadóir mise

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

Cad é mar a déarfá "dumb, persistent, beginner's luck" as Gaeilge?

I ndairíre, tá cóip "Essential Irish Grammar" agam, ach ní féidir liom é a fháil. Tá mé ag glanadh tí.

Redwolf

Graiméar Gaeilge na mBráithre Críostaí - "Bíobla" na Gaeilge.

Like the numbers, I don't believe anyone truly knows. sometimes i see two words where there is lenition and wonder if it is also just when two words are used next to each other for a long time tey just fuse, as well

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__̴ı̴̴̡̡̡ ̡͌l̡̡̡ ̡͌l̡*̡̡ ̴̡ı̴̴̡ ̡̡͡|̲̲̲͡͡͡ ̲▫̲͡ ̲̲̲͡͡π̲̲͡͡ ̲̲͡▫̲̲͡͡ ̲|̡̡̡ ̡ ̴̡ı̴̡̡ ̡͌l̡̡̡̡.___