a fhios a bheith agat
- to know (be certain or sure about (something); have knowledge of; be informed about)
Tá a fhios agam go bhfuil an ceart agam.
- I know that I am right.
An raibh fios an scéil ag Seán?
- Did John know about the matter?
Literally means "its knowledge is at you". The tense of English know is reflected by the tense of the verb "to be" in Irish, while the subject of know in English is the object of the preposition ag in Irish. A noun governed by about in English is rendered by a genitive in Irish, in which case a fhios becomes simply fios.