tá aiṫne agam, and tá a ḟios agam, all meaning “I know;” but these three expressions have three different meanings which must be carefully distinguished.
Whenever the English verb “know” means “to know by heart” or “to know the character of a person,” “to know by study,” &c., use the phrase tá eolas ag … ar.
Whenever “know” means “to recognise,” “to know by appearance,” “to know by sight,” &c., use the phrase tá aiṫne ag … ar. This phrase is usually restricted to persons.
When “know” means “to know by mere information,” “to happen to know,” as in such a sentence as “Do you know did John come in yet?” use the phrase tá a ḟios ag, e.g. Ḃfuil a ḟios agat an dtáinig Seaġán isteaċ fós?
As a rule young students experience great difficulty in selecting the phrases to be used in a given case. This difficulty arises entirely from not striving to grasp the real meaning of the English verb. For those who have already learned French it may be useful to state that as a general rule tá eolas agam corresponds to je sais and tá aiṫne agam to je connais.
Tá aiṫne agam air aċt ní ḟuil eolas agam air. Je le connais mais je ne le sais pas. I know him by sight but I do not know his character. “Do you know
