"I thought that I bought beer."

Translation: Cheap mé gur cheannaigh mé beoir.

[deserttitan]

Gur is past tense of go?

[scilling]

It’s not technically a past tense (since it’s a conjunction, and conjunctions don’t have tenses), but this gur is only used before a regular verb in the past tense.

[foolimeoir]

Could you say something like "cheap mé go raibh beoir cheannaítear agam"

[scilling]

That’s somewhat scrambled in Irish. Which English sentence are you trying to express in Irish?

[4meerschweinchen]

you can't use 'go raibh' instead of 'gur' here?

[scilling]

The two consecutive verbs in go raibh cheannaigh mé don’t make sense.

[pvcsweeney]

Why "gur" and no "go"?

[scilling]

See my reply to deserttitan above.

[MacSuibhne]

Does "cheapaim" not make sense for "cheap mé" here?

[centonola]

In the present tense you do indeed have the option of the one-word form for the first person singular: ceapaim. But in the past tense, you always have to use the form "Verb + mé" for the first person. "Cheapaim" doesn't exist.

[Noel467439]

We use "cheapas" all the time in Munster. And, indeed, most verbs can have an "(e)as" ending instead verb+mé in the past tense

[K4ttan]

Cheap mé gur

cheannaigh mé beoir.

Almost rhymes, that. I say "almost" because I'm not sure of my pronunciation.

[SatharnPHL]

Different vowel sounds, and the slender r in beoir doesn't sound like the broad r in gur.